Metals

9 pages, 7232 KiB

Open AccessArticle

The Effect of Cold Rolling on the Hydrogen Susceptibility of 5083 Aluminum Alloy

by E.P. Georgiou^1,2,*

, J.-P. Celis¹ and C.N. Panagopoulos³

¹ Department Materials Engineering (MTM), K.U. Leuven, Kasteelpark Arenberg 44, B-3001 Leuven, Belgium

² Falex Tribology N.V., Wingepark 23B, B3110 Rotselaar, Belgium

³ Laboratory of Physical Metallurgy, National Technical University of Athens, Zografos, 15780 Athens, Greece

Metals 2017, 7(11), 451; https://doi.org/10.3390/met7110451 - 25 Oct 2017

Cited by 14 | Viewed by 6707

Abstract

This work focuses in investigating the effect of cold deformation on the cathodic hydrogen charging of 5083 aluminum alloy. The aluminium alloy was submitted to a cold rolling process, until the average thickness of the specimens was reduced by 7% and 15%, respectively. [...] Read more.

This work focuses in investigating the effect of cold deformation on the cathodic hydrogen charging of 5083 aluminum alloy. The aluminium alloy was submitted to a cold rolling process, until the average thickness of the specimens was reduced by 7% and 15%, respectively. A study of the structure, microhardness, and tensile properties of the hydrogen charged aluminium specimens, with and without cold rolling, indicated that the cold deformation process led to an increase of hydrogen susceptibility of this aluminum alloy. Full article

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12 pages, 17384 KiB

Open AccessArticle

Control of Porosity and Spatter in Laser Welding of Thick AlMg5 Parts Using High-Speed Imaging and Optical Microscopy

by Andrei C. Popescu^1,2,*, Christophe Delval¹ and Marc Leparoux¹

¹ Laboratory of Advanced Materials Processing, EMPA-Swiss Federal Laboratories for Materials Testing and Research, Feuerwerkerstrasse 39, 3602 Thun, Switzerland

² National Institute for Lasers, Plasma and Radiation Physics, Atomistilor 409, 077125 Magurele, Romania

Metals 2017, 7(11), 452; https://doi.org/10.3390/met7110452 - 26 Oct 2017

Cited by 19 | Viewed by 9475

Abstract

We report on a feedback mechanism for rapid identification of optimal laser parameters during welding of AlMg5 coupons using real-time monitoring by high-speed imaging. The purpose was to constrain the liquid movement in the groove in order to obtain pore-free welds in this [...] Read more.

We report on a feedback mechanism for rapid identification of optimal laser parameters during welding of AlMg5 coupons using real-time monitoring by high-speed imaging. The purpose was to constrain the liquid movement in the groove in order to obtain pore-free welds in this otherwise difficult-to-weld alloy. High-speed imaging of the welding process via an optical microscope allowed for recording at millimeter level, providing new information on liquid-metal dynamics during laser irradiation as well as plausible explanations for spatter occurrence and pores formation. The pore formation and especially the position of these pores had to be controlled in order to weld 3 mm thick samples. By tuning both laser power and pulse duration, pores were aligned on a single line, at the bottom of the weld. A laser pass of reduced power on that side was then sufficient for removing all pores and providing a suitable weld. Full article

(This article belongs to the Special Issue Laser Welding)

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Graphical abstract

15 pages, 10241 KiB

Open AccessArticle

A Novel Hybrid Actuator Driven Magnetically in the Bi-Cell PEM Fuel Cell Stack

by Hsiaokang Ma, Yuanlung Hsu^* and Poching Hsu

Department of Mechanical Engineering, National Taiwan University, Taipei 10617, Taiwan

Metals 2017, 7(11), 453; https://doi.org/10.3390/met7110453 - 26 Oct 2017

Cited by 3 | Viewed by 6349

Abstract

This study develops an air breathing pump driven by a piezoelectric actuator for a proton exchange membrane fuel cell (PEMFC) stack. Permanent magnets are combined with a piezoelectric actuator to drive three air breathing pumps using magnetic force. This design enables the pump [...] Read more.

This study develops an air breathing pump driven by a piezoelectric actuator for a proton exchange membrane fuel cell (PEMFC) stack. Permanent magnets are combined with a piezoelectric actuator to drive three air breathing pumps using magnetic force. This design enables the pump to provide a sufficient amount of air simultaneously to six cathode flow field plates in a stack of three “bi-cell PZTmag–PEMFCs”. When both the PZTmag and the PDMSmag had a magnet with a 6-mm diameter and 1-mm thickness, a maximum amplitude of 87 μm was generated at 0.03 W of power under operating conditions of 70 Hz and 40 V. In computational fluid dynamics (CFD), when the nozzle and the diffuser of an air breathing pump have an aspect ratio of 13.13, air flow distributes uniformly inside the pump, thus allowing for uniform transmission of oxygen to the membrane electrode assembly. This aspect ratio was applied to the bi-cell PZTmag–PEMFC stack and yielded a maximum net power flux of 0.1925 W·cm⁻², 20% higher than that reported in a previous study (Ma, 2013), with 68% and 76% less volume and weight, respectively. Full article

(This article belongs to the Special Issue Piezoelectric Materials and Applications)

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11 pages, 4402 KiB

Open AccessArticle

Laser Pulse Effects on Plasma-Sprayed and Bulk Tungsten

by Roberto Montanari^*

, Ekaterina Pakhomova, Roberto Pizzoferrato

, Maria Richetta and Alessandra Varone

Department of Industrial Engineering, University of Rome Tor Vergata, 00133 Rome, Italy

Metals 2017, 7(11), 454; https://doi.org/10.3390/met7110454 - 26 Oct 2017

Cited by 17 | Viewed by 3981

Abstract

Tungsten (W) is considered a promising plasma-facing material for protecting the divertor of the ITER (International Thermonuclear Experimental Reactor). The effects on W of transient thermal loads of high energy occurring in a tokamak under operative conditions have been simulated through a single [...] Read more.

Tungsten (W) is considered a promising plasma-facing material for protecting the divertor of the ITER (International Thermonuclear Experimental Reactor). The effects on W of transient thermal loads of high energy occurring in a tokamak under operative conditions have been simulated through a single laser pulse delivered by an Nd:YAG laser. Bulk and plasma-sprayed (PS) samples have been submitted to tests and successively examined via SEM (scanning electron microscopy) observations. In both types of materials, the laser pulse induces similar effects: (i) a crater forms in the spot central area; (ii) all around the area, the ejection and the movement of molten metal give rise to a ridge; (iii) in a more external area, the surface shows plates with jagged boundaries and cracks induced by thermal stresses; (iv) the pores present in the original material become preferred ablation sites. However, the affected surface area in PS samples is larger and asymmetric if compared to that of bulk material. Such a difference has been explained by considering how microstructural characteristics influence heat propagation from the irradiated spot, and it was found that grain size and shape play a decisive role. Full article

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18 pages, 5405 KiB

Open AccessArticle

Numerical Predictions of the Occurrence of Necking in Deep Drawing Processes

by Hocine Chalal and Farid Abed-Meraim^*

LEM3, UMR CNRS 7239—Arts et Métiers ParisTech, 4, rue Augustin Fresnel, 57078 Metz CEDEX 03, France

Metals 2017, 7(11), 455; https://doi.org/10.3390/met7110455 - 27 Oct 2017

Cited by 12 | Viewed by 6067

Abstract

In this work, three numerical necking criteria based on finite element (FE) simulations are proposed for the prediction of forming limit diagrams (FLDs) for sheet metals. An elastic–plastic constitutive model coupled with the Lemaitre continuum damage theory has been implemented into the ABAQUS/Explicit [...] Read more.

In this work, three numerical necking criteria based on finite element (FE) simulations are proposed for the prediction of forming limit diagrams (FLDs) for sheet metals. An elastic–plastic constitutive model coupled with the Lemaitre continuum damage theory has been implemented into the ABAQUS/Explicit software to simulate simple sheet stretching tests as well as Erichsen deep drawing tests with various sheet specimen geometries. Three numerical criteria have been investigated in order to establish an appropriate necking criterion for the prediction of formability limits. The first numerical criterion is based on the analysis of the thickness strain evolution in the central part of the specimens. The second numerical criterion is based on the analysis of the second time derivative of the thickness strain. As to the third numerical criterion, it relies on a damage threshold associated with the occurrence of necking. The FLDs thus predicted by numerical simulation of simple sheet stretching with various specimen geometries and Erichsen deep drawing tests are compared with the experimental results. Full article

(This article belongs to the Special Issue Advances in Plastic Forming of Metals)

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18 pages, 9237 KiB

Open AccessArticle

CO₂ Laser Cutting of Hot Stamping Boron Steel Sheets

by Pasquale Russo Spena

Faculty of Science and Technology, Free University of Bozen-Bolzano, 39100 Bolzano, Italy

Metals 2017, 7(11), 456; https://doi.org/10.3390/met7110456 - 27 Oct 2017

Cited by 15 | Viewed by 6865

Abstract

This study investigates the quality of CO₂ laser cutting of hot stamping boron steel sheets that are employed in the fabrication of automotive body-in-white. For this purpose, experimental laser cutting tests were conducted on 1.2 mm sheets at varying levels of laser [...] Read more.

This study investigates the quality of CO₂ laser cutting of hot stamping boron steel sheets that are employed in the fabrication of automotive body-in-white. For this purpose, experimental laser cutting tests were conducted on 1.2 mm sheets at varying levels of laser power, cutting speed, and oxygen pressure. The resulting quality of cut edges was evaluated in terms of perpendicularity tolerance, surface irregularity, kerf width, heat affected zone, and dross extension. Experimental tests were based on a L9(3⁴) orthogonal array design, with the effects of the process parameters on the quality responses being determined by means of a statistical analysis of variance (ANOVA). Quadratic mathematical models were developed to determine the relationships between the cutting parameters and the quality responses. Finally, a routine based on an optimization criterion was employed to predict the optimal setting of cutting factors and its effect on the quality responses. A confirmation experiment was conducted to verify the appropriateness of the optimization routine. The results show that all of the examined process parameters have a key role in determining the cut quality of hot stamping boron steel sheets, with cutting speed and their interactions having the most influencing effects. Particularly, interactions can have an opposite behavior for different levels of the process parameters. Full article

(This article belongs to the Special Issue Metals Machining – Recent Advances in Experimental and Modeling of the Cutting Process)

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13 pages, 14913 KiB

Open AccessFeature PaperArticle

Study of the Influence of TiB Content and Temperature in the Properties of In Situ Titanium Matrix Composites

by Cristina Arévalo¹, Isabel Montealegre-Melendez^1,*, Eva M. Pérez-Soriano¹

, Enrique Ariza²

, Michael Kitzmantel² and Erich Neubauer²

¹ Department of Engineering and Materials Science and Transportation, School of Engineering, Universidad de Sevilla, Camino de los Descubrimientos s/n, 41092 Seville, Spain

² RHP-Technology GmbH, Forschungs- und Technologiezentrum, 2444 Seibersdorf, Austria

Metals 2017, 7(11), 457; https://doi.org/10.3390/met7110457 - 27 Oct 2017

Cited by 5 | Viewed by 4451

Abstract

This work focuses on the study of the microstructure, hardening, and stiffening effect caused by the secondary phases formed in titanium matrices. These secondary phases originated from reactions between the matrix and boron particles added in the starting mixtures of the composites. Not [...] Read more.

This work focuses on the study of the microstructure, hardening, and stiffening effect caused by the secondary phases formed in titanium matrices. These secondary phases originated from reactions between the matrix and boron particles added in the starting mixtures of the composites. Not only was the composite composition studied as an influencing factor in the behaviour of the composites, but also different operational temperatures. Three volume percentages of boron content were tested (0.9 vol %, 2.5 vol %, and 5 vol % of amorphous boron). The manufacturing process used to produce the composites was inductive hot pressing, which operational temperatures were between 1000 and 1300 °C. Specimens showed optimal densification. Moreover, microstructural studies revealed the formation of TiB in various shapes and proportions. Mechanical testing confirmed that the secondary phases had a positive influence on properties of the composites. In general, adding boron particles increased the hardness and stiffness of the composites; however rising temperatures resulted in greater increases in stiffness than in hardness. Full article

(This article belongs to the Special Issue Metal Matrix Composites)

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11 pages, 5820 KiB

Open AccessArticle

A Mineralogical Assessment on Residues after Acidic Leaching of Bauxite Residue (Red Mud) for Titanium Recovery

by Gözde Alkan^1,*, Claudia Schier¹, Lars Gronen²

, Srecko Stopic¹ and Bernd Friedrich¹

¹ IME-Process Metallurgy and Metal Recycling, RWTH Aachen University, Intzestraße 3, 52056 Aachen, Germany

² IML-Chair of Applied Mineralogy and Economic Geology, RWTH Aachen University, Wüllnerstraße 2, 52062 Aachen, Germany

Metals 2017, 7(11), 458; https://doi.org/10.3390/met7110458 - 28 Oct 2017

Cited by 51 | Viewed by 7359

Abstract

Due to its alkalinity, red mud produced by the Bayer process may affect both the environment and human health. For this reason, its further utilization instead of disposal is of great importance. Numerous methods have already been studied for hydrometallurgical treatment of red [...] Read more.

Due to its alkalinity, red mud produced by the Bayer process may affect both the environment and human health. For this reason, its further utilization instead of disposal is of great importance. Numerous methods have already been studied for hydrometallurgical treatment of red mud, especially for the recovery of various metallic components such as iron, aluminum, titanium or rare earth elements. This study focuses on the extraction of titanium from red mud and in particular the mineralogical changes, induced by leaching. Sulfuric acid, hydrochloric acid and their combination have been utilized as leaching agents with the same leaching parameters. It has been determined that sulfuric acid is the best candidate for the red mud treatment in terms of titanium leaching efficiency at the end of 2 h with a value of 67.3%. Moreover, samples from intermediate times of reaction revealed that leaching of Ti exhibit various reaction rates at different times of reaction depending on acid type. In order to explain differences, X-ray Diffraction (XRD), scanning electron microscope (SEM) and QEMSCAN techniques were utilized. Beside titanium oxide (TiO₂) with available free surface area, a certain amount of the TiO₂ was detected as entrapped in Fe dominating oxide. These associations between Ti and Fe phases were used to explain different leaching reaction rates and a reaction mechanism was proposed to open a process window. Full article

(This article belongs to the Special Issue Advances in Hydrometallurgy)

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13 pages, 4182 KiB

Open AccessFeature PaperArticle

Crystal Plasticity Modeling and Experimental Validation with an Orientation Distribution Function for Ti-7Al Alloy

by Pınar Acar

, Ali Ramazani^*

and Veera Sundararaghavan

Aerospace Engineering, University of Michigan, Ann Arbor, MI 48109, USA

Metals 2017, 7(11), 459; https://doi.org/10.3390/met7110459 - 28 Oct 2017

Cited by 37 | Viewed by 5719

Abstract

An orientation distribution function based model is used for micromechanical modeling of the titanium-aluminum alloys, Ti-0 wt % Al and Ti-7 wt % Al, which are in demand for many aerospace applications. This probability descriptor based modeling approach is different than crystal plasticity [...] Read more.

An orientation distribution function based model is used for micromechanical modeling of the titanium-aluminum alloys, Ti-0 wt % Al and Ti-7 wt % Al, which are in demand for many aerospace applications. This probability descriptor based modeling approach is different than crystal plasticity finite element techniques since it computes the averaged material properties using upper bound averaging. A rate-independent single-crystal plasticity model is implemented to compute the effect of macroscopic strain on the polycrystal. An optimization problem is defined for calibrating the basal, prismatic, pyramidal slip system and twin parameters using the available tension and compression experimental data. The crystal plasticity parameters of Ti-7 wt % Al are not studied extensively in literature, and therefore the optimization results for the crystal plasticity model realization produce unique data, which will be beneficial to future studies in the field. The sensitivities of the slip and twin parameters to the design objectives are also investigated to identify the most critical slip system parameters. Using the optimum design parameters, the microstructural textures, during the tension test, are predicted by the crystal plasticity finite element simulations, and compared to the available experimental texture and scanning electron microscope—digital image correlation data. Full article

(This article belongs to the Special Issue Microstructure based Modeling of Metallic Materials)

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31 pages, 3847 KiB

Open AccessReview

Modeling Inclusion Formation during Solidification of Steel: A Review

by Dali You^1,*, Susanne K. Michelic¹, Peter Presoly¹, Jianhua Liu² and Christian Bernhard^1,*

¹ Chair of Ferrous Metallurgy, Montanuniversität Leoben, Franz-Josef-Straße 18, 8700 Leoben, Austria

² Engineering Research Institute, University of Science and Technology Beijing, Haidian District Xueyuan Road 30, Beijing 100083, China

Metals 2017, 7(11), 460; https://doi.org/10.3390/met7110460 - 30 Oct 2017

Cited by 57 | Viewed by 8758

Abstract

The formation of nonmetallic inclusions in the solidification process can essentially influence the properties of steels. Computational simulation provides an effective and valuable method to study the process due to the difficulty of online investigation. This paper reviews the modeling work of inclusion [...] Read more.

The formation of nonmetallic inclusions in the solidification process can essentially influence the properties of steels. Computational simulation provides an effective and valuable method to study the process due to the difficulty of online investigation. This paper reviews the modeling work of inclusion formation during the solidification of steel. Microsegregation and inclusion formation thermodynamics and kinetics are first introduced, which are the fundamentals to simulate the phenomenon in the solidification process. Next, the thermodynamic and kinetic models coupled with microsegregation dedicated to inclusion formation are briefly described and summarized before the development and future expectations are discussed. Full article

(This article belongs to the Special Issue Recent Advances in Study of Solid-Liquid Interfaces and Solidification of Metals)

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22 pages, 7070 KiB

Open AccessArticle

Characterization of Powder Metallurgy Processed Pure Magnesium Materials for Biomedical Applications

by Matěj Březina^1,*, Jozef Minda¹, Pavel Doležal^1,2

, Michaela Krystýnová¹, Stanislava Fintová^1,3

, Josef Zapletal², Jaromír Wasserbauer¹ and Petr Ptáček¹

¹ Materials Research Centre, Faculty of Chemistry, Brno University of Technology, Purkyňova 464/118, 61200 Brno, Czech Republic

² Institute of Materials Science and Engineering, Faculty of Mechanical Engineering, Brno University of Technology, Technická 2896/2, 61669 Brno, Czech Republic

³ Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 61662 Brno, Czech Republic

Metals 2017, 7(11), 461; https://doi.org/10.3390/met7110461 - 31 Oct 2017

Cited by 26 | Viewed by 8152

Abstract

Magnesium with its mechanical properties and nontoxicity is predetermined as a material for biomedical applications; however, its high reactivity is a limiting factor for its usage. Powder metallurgy is one of the promising methods for the enhancement of material mechanical properties and, due [...] Read more.

Magnesium with its mechanical properties and nontoxicity is predetermined as a material for biomedical applications; however, its high reactivity is a limiting factor for its usage. Powder metallurgy is one of the promising methods for the enhancement of material mechanical properties and, due to the introduced plastic deformation, can also have a positive influence on corrosion resistance. Pure magnesium samples were prepared via powder metallurgy. Compacting pressures from 100 MPa to 500 MPa were used for samples’ preparation at room temperature and elevated temperatures. The microstructure of the obtained compacts was analyzed in terms of microscopy. The three-point bendisng test and microhardness testing were adopted to define the compacts’ mechanical properties, discussing the results with respect to fractographic analysis. Electrochemical corrosion properties analyzed with electrochemical impedance spectroscopy carried out in HBSS (Hank’s Balanced Salt Solution) and enriched HBSS were correlated with the metallographic analysis of the corrosion process. Cold compacted materials were very brittle with low strength (up to 50 MPa) and microhardness (up to 50 HV (load: 0.025 kg)) and degraded rapidly in both solutions. Hot pressed materials yielded much higher strength (up to 250 MPa) and microhardness (up to 65 HV (load: 0.025 kg)), and the electrochemical characteristics were significantly better when compared to the cold compacted samples. Temperatures of 300 °C and 400 °C and high compacting pressures from 300 MPa to 500 MPa had a positive influence on material bonding, mechanical and electrochemical properties. A compacting temperature of 500 °C had a detrimental effect on material compaction when using pressure above 200 MPa. Full article

(This article belongs to the Special Issue Biodegradable Metals)

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19 pages, 4399 KiB

Open AccessArticle

Prediction of the Geometrical Accuracy of the Machined Surface of the Tool Steel EN X30WCrV9-3 after Electrical Discharge Machining with CuZn37 Wire Electrode

by Ľuboslav Straka^1,*

, Ivan Čorný²

and Ján Piteľ³

¹ Department of Automobile and Manufacturing Technologies, The Technical University of Košice, Štúrova 31, Prešov 08001, Slovakia

² Department of Process Engineering, The Technical University of Košice, Štúrova 31, Prešov 08001, Slovakia

³ Department of Industrial Engineering and Informatics, The Technical University of Košice, Bayerova 1, Prešov 08001, Slovakia

Metals 2017, 7(11), 462; https://doi.org/10.3390/met7110462 - 31 Oct 2017

Cited by 20 | Viewed by 4264

Abstract

The geometrical accuracy of the machined surface can generally be understood mainly as accuracy of shape, orientation, position and run-out. As a general rule; it is quantified by the corresponding deviations from the nominal area. The size of the geometric deviation from the [...] Read more.

The geometrical accuracy of the machined surface can generally be understood mainly as accuracy of shape, orientation, position and run-out. As a general rule; it is quantified by the corresponding deviations from the nominal area. The size of the geometric deviation from the nominal area may in practice affect the conventionally measured value of the dimension, even if the required dimensional tolerance is adhered to. Since electro–erosive machining technology belongs to very precise finishing technologies; even the small geometrical accuracy deviation has a negative impact on the resulting quality of machined surfaces. The aim of the experiments was to contribute to the knowledge database, which defines the influence of the process parameters at electrical discharge machining with the CuZn37 tool electrode on errors of geometrical accuracy of the machined surface. On the basis of the results of the experimental measurements, graphical dependencies were determined which predict geometrical accuracy of the machined surface in terms of the maximum deviation of flatness after electrical discharge machining of tool steel EN X30WCrV9-3 (W.-Nr. 1.2581) with CuZn37 wire electrode of 0.20 mm diameter to determine the appropriate combination of process parameters. Full article

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17 pages, 18110 KiB

Open AccessArticle

Effects of Porosity, Heat Input and Post-Weld Heat Treatment on the Microstructure and Mechanical Properties of TIG Welded Joints of AA6082-T6

by Bo Wang¹, Songbai Xue^1,*

, Chaoli Ma¹, Jianxin Wang² and Zhongqiang Lin³

¹ College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

² Jiangsu Provincial Key Laboratory of Advanced Welding Technology, Jiangsu University of Science and Technology, Zhenjiang 212003, China

³ Zhejiang Yuguang Aluminum Material Co., Ltd., Jinhua 321200, China

Metals 2017, 7(11), 463; https://doi.org/10.3390/met7110463 - 1 Nov 2017

Cited by 26 | Viewed by 8130

Abstract

Various heat input conditions and post-weld heat treatments were adopted to investigate the microstructure evolution and mechanical properties of tungsten inert gas (TIG) welded joints of AA6082-T6 with porosity defects. The results show that the fracture location is uncertain when an as-welded joint [...] Read more.

Various heat input conditions and post-weld heat treatments were adopted to investigate the microstructure evolution and mechanical properties of tungsten inert gas (TIG) welded joints of AA6082-T6 with porosity defects. The results show that the fracture location is uncertain when an as-welded joint has porosities in the weld zone (WZ), and overaging in the heat-affected zone (HAZ) at the same time. When the fracture of the as-welded joint occurs in the HAZ, the total heat input has a linear relation with the tensile strength of the joint. An excess heat input induces the overgrowth of Mg₂Si precipitates in HAZ and the coarsening of α-Al grains in WZ, resulting in a decrease in the microhardness of the corresponding areas. After artificial aging treatment, the tensile strength of the welded joint is increased by approximately 9–13% as compared to that of as-welded joint, and fracture also occurs in HAZ. In contrast, for solution treated and artificial aging treated joint, fracture occurs suddenly at the rising phase of the tensile curve due to porosity defects throughout the weld metal. Furthermore, the eutectic Si particles of WZ coarsen and spheroidize after solution treatment and artificial aging treatment, due to the diffusion of Si to the surface of the original Si phases when soaking at high temperature. Full article

(This article belongs to the Special Issue Heat Treatment of Aluminum Alloys)

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11 pages, 13687 KiB

Open AccessArticle

Microstructures and Mechanical Properties of 7Mn Steel Manufactured by Different Rolling Processes

by Bin Hu¹

and Haiwen Luo^1,2,*

¹ School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Xue Yuan Lu 30, Beijing 100083, China

² Central Iron and Steel Research Institute, Xue Yuan Nan Lu 30, Beijing 100081, China

Metals 2017, 7(11), 464; https://doi.org/10.3390/met7110464 - 1 Nov 2017

Cited by 22 | Viewed by 5793

Abstract

We investigated both the microstructures and tensile properties of 7Mn steel, which was either hot-rolled, warm-rolled or cold-rolled before intercritical annealing at 700 °C for 5 h. It can be concluded that the warm-rolled and annealed microstructures are a kind of mixture of [...] Read more.

We investigated both the microstructures and tensile properties of 7Mn steel, which was either hot-rolled, warm-rolled or cold-rolled before intercritical annealing at 700 °C for 5 h. It can be concluded that the warm-rolled and annealed microstructures are a kind of mixture of hot rolled and cold rolled ones. They are composed of ferrite and retained austenite, the latter having a wide size distribution and two types of morphologies: equiaxed and lamellar. These retained austenite grains are expected to transform to martensite in a more sustainable way—the warm-rolled and annealed steel exhibits the best combination of ultimate tensile strength and total elongation among the three studied steels and a shorter yield point elongation than the cold-rolled one. Full article

(This article belongs to the Special Issue Medium-Mn Steels, a Promising Type of the 3rd Generation Steels)

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17 pages, 10157 KiB

Open AccessArticle

Influence of the Composition of the Hank’s Balanced Salt Solution on the Corrosion Behavior of AZ31 and AZ61 Magnesium Alloys

by Jakub Tkacz^1,2,*

, Karolína Slouková¹, Jozef Minda¹, Juliána Drábiková¹, Stanislava Fintová^1,3

, Pavel Doležal^1,4

and Jaromír Wasserbauer¹

¹ Materials Research Centre, Faculty of Chemistry, Brno University of Technology, 612 00 Brno, Czech Republic

² Research Centre, University of Žilina, 010 08 Žilina, Slovakia

³ Institute of Physics of Materials AS CR v. v. i., Žižkova 22, 616 62 Brno, Czech Republic

⁴ Institute of Materials Science and Engineering, Faculty of Mechanical Engineering, Brno University of Technology, Technická 2896/2, 616 69 Brno, Czech Republic

Metals 2017, 7(11), 465; https://doi.org/10.3390/met7110465 - 1 Nov 2017

Cited by 46 | Viewed by 8015

Abstract

The electrochemical corrosion characteristics of AZ31 and AZ61 magnesium alloys were analyzed in terms of potentiodynamic tests and electrochemical impedance spectroscopy. The influence of the solution composition and material surface finish was examined also through the analysis of corrosion products created on the [...] Read more.

The electrochemical corrosion characteristics of AZ31 and AZ61 magnesium alloys were analyzed in terms of potentiodynamic tests and electrochemical impedance spectroscopy. The influence of the solution composition and material surface finish was examined also through the analysis of corrosion products created on the samples’ surface after electrochemical measurements in terms of scanning electron microscopy using energy-dispersive spectroscopy. Obtained data revealed the differences in the response of the magnesium alloys to enriched Hank’s Balanced Salt Solution—HBSS+ (with Mg²⁺ and Ca²⁺ ions) and Hank’s Balanced Salt Solution—HBSS (without Mg²⁺ and Ca²⁺ ions). Both examined alloys exhibited better corrosion resistance from the thermodynamic and kinetic point of view in the enriched HBSS+. AZ61 magnesium alloy reached higher values of polarization resistance than AZ31 magnesium alloy in both the used corrosion solutions. Phosphate-based corrosion products were characteristic for the AZ31 and AZ61 alloys tested in the HBSS (without Mg²⁺ and Ca²⁺ ions). The combination of phosphate-based corrosion products and clusters of MgO and Mg(OH)₂ was typical for the surface of samples tested in the enriched HBSS+ (with Mg²⁺ and Ca²⁺ ions). Pitting corrosion attack was observed only in the case of enriched HBSS+. Full article

(This article belongs to the Special Issue Biodegradable Metals)

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18 pages, 7571 KiB

Open AccessArticle

Fatigue Crack Growth Behavior of Austempered AISI 4140 Steel with Dissolved Hydrogen

by Varun Ramasagara Nagarajan¹, Susil K. Putatunda^1,* and James Boileau²

¹ Department of Chemical Engineering and Materials Science, Wayne State University, Detroit, MI 48202, USA

² Research and Innovation Center, Ford Motor Company, Dearborn, MI 48121, USA

Metals 2017, 7(11), 466; https://doi.org/10.3390/met7110466 - 1 Nov 2017

Cited by 15 | Viewed by 8831

Abstract

The focus of this investigation was to examine the influence of dissolved hydrogen on the fatigue crack growth behavior of an austempered low-alloy AISI 4140 steel. The investigation also examined the influence of dissolved hydrogen on the fatigue threshold in this material. The [...] Read more.

The focus of this investigation was to examine the influence of dissolved hydrogen on the fatigue crack growth behavior of an austempered low-alloy AISI 4140 steel. The investigation also examined the influence of dissolved hydrogen on the fatigue threshold in this material. The material was tested in two conditions, as-received (cold rolled and annealed) and austempered (austenitized at 882 °C for 1 h and austempered at 332 °C for 1 h). The microstructure of the annealed specimens consisted of a mix of ferrite and fine pearlite; the microstructure of the austempered specimens was lower bainite. Tensile and Compact Tension specimens were prepared. To examine the influence of dissolved hydrogen, two subsets of the CT specimens were charged with hydrogen for three different time periods between 150 and 250 h. All of the CT samples were then subjected to fatigue crack growth tests in the threshold and linear regions at room temperature. The test results indicate that austempering resulted in significant improvement in the yield and tensile strength as well as the fracture toughness of the material. The test results also show that, in the absence of dissolved hydrogen, the crack growth rate in the threshold and linear regions was lower in austempered samples compared to the as-received (annealed) samples. The fatigue threshold was also slightly greater in the austempered samples. In presence of dissolved hydrogen, the crack growth rate was dependent upon the ∆K value. In the low ∆K region (<30 MPa√m), the presence of dissolved hydrogen caused the crack growth rate to be higher in the austempered samples as compared to annealed samples. Above this value, the crack growth rate was increasingly greater in the annealed specimens when compared to the austempered specimens in presence of dissolved hydrogen. It is concluded that austempering of 4140 steel appears to provide a processing route by which the strength, hardness, and fracture toughness of the material can be increased with little or no degradation in the ductility and fatigue crack growth behavior. Full article

(This article belongs to the Special Issue Environmentally Assisted Cracking in Advanced High Strength Alloys)

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14 pages, 17172 KiB

Open AccessArticle

Experimental Investigation on Electric Current-Aided Laser Stake Welding of Aluminum Alloy T-Joints

by Xinge Zhang^1,2,*, Liqun Li², Yanbin Chen², Zhaojun Yang¹ and Xiaocui Zhu¹

¹ School of Mechanical Science and Engineering, Jilin University, Changchun 130025, China

² State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, China

Metals 2017, 7(11), 467; https://doi.org/10.3390/met7110467 - 1 Nov 2017

Cited by 9 | Viewed by 5711

Abstract

In the present study, aluminum alloy T-joints were welded using the laser stake-welding process. In order to improve the welding quality of the T-joints, an external electric current was used to aid the laser stake-welding process. The effects of the process parameters on [...] Read more.

In the present study, aluminum alloy T-joints were welded using the laser stake-welding process. In order to improve the welding quality of the T-joints, an external electric current was used to aid the laser stake-welding process. The effects of the process parameters on the weld morphology, mechanical properties, and microstructure of the welded joints were analyzed and discussed in detail. The results indicate that the aided electric current should be no greater than a certain maximum value. Upon increasing the aided electric current, the weld width at the skin and stringer faying surface obviously increased, but there was an insignificant change in the penetration depth. Furthermore, the electric current and pressing force should be chosen to produce an expected weld width at the faying surface, whereas the laser power and welding speed should be primarily considered to obtain an optimal penetration depth. The tensile shear specimens failed across the faying surface or failed in the weld zone of the skin. The specimens that failed in the weld of the skin could resist a higher tensile shear load compared with specimens that failed across the faying surface. The microstructural observations and microhardness results demonstrated that the tensile shear load capacity of the aluminum alloy welded T-joint was mainly determined by the weld width at the faying surface. Full article

(This article belongs to the Special Issue Laser Welding)

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19 pages, 2934 KiB

Open AccessOpinion

Osseoconductive and Corrosion-Inhibiting Plasma-Sprayed Calcium Phosphate Coatings for Metallic Medical Implants

by Robert B. Heimann

Am Stadtpark 2A, D-02826 Görlitz, Germany

Metals 2017, 7(11), 468; https://doi.org/10.3390/met7110468 - 1 Nov 2017

Cited by 34 | Viewed by 6405

Abstract

During the last several decades, research into bioceramic coatings for medical implants has emerged as a hot topic among materials scientists and clinical practitioners alike. In particular, today, calcium phosphate-based bioceramic materials are ubiquitously used in clinical applications to coat the stems of [...] Read more.

During the last several decades, research into bioceramic coatings for medical implants has emerged as a hot topic among materials scientists and clinical practitioners alike. In particular, today, calcium phosphate-based bioceramic materials are ubiquitously used in clinical applications to coat the stems of metallic endoprosthetic hips as well as the surfaces of dental root implants. Such implants frequently consist of titanium alloys, CoCrMo alloy, or austenitic surgical stainless steels, and aim at replacing lost body parts or restoring functions to diseased or damaged tissues of the human body. In addition, besides such inherently corrosion-resistant metals, increasingly, biodegradable metals such as magnesium alloys are being researched for osseosynthetic devices and coronary stents both of which are intended to remain in the human body for only a short time. Biocompatible coatings provide not only vital biological functions by supporting osseoconductivity but may serve also to protect the metallic parts of implants from corrosion in the aggressive metabolic environment. Moreover, the essential properties of hydroxylapatite-based bioceramic coatings including their in vitro alteration in contact with simulated body fluids will be addressed in this current review paper. In addition, a paradigmatic shift is suggested towards the development of transition metal-substituted calcium hexa-orthophosphates with the NaSiCON (Na superionic conductor) structure to be used for implant coatings with superior degradation resistance in the corrosive body environment and with pronounced ionic conductivity that might be utilized in novel devices for electrical bone growth stimulation. Full article

(This article belongs to the Special Issue Advances in Enhancing Degradation Resistance of Metallic Implants by Surface Engineering)

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16 pages, 735 KiB

Open AccessArticle

On the Use of Maximum Force Criteria to Predict Localised Necking in Metal Sheets under Stretch-Bending

by Domingo Morales-Palma^*

, Andrés J. Martínez-Donaire and Carpóforo Vallellano

Department of Mechanical Engineering and Manufacturing, University of Seville, Camino de los Descubrimientos s/n, 41092 Seville, Spain

Metals 2017, 7(11), 469; https://doi.org/10.3390/met7110469 - 2 Nov 2017

Cited by 12 | Viewed by 5095

Abstract

The maximum force criteria and their derivatives, the Swift and Hill criteria, have been extensively used in the past to study sheet formability. Many extensions or modifications of these criteria have been proposed to improve necking predictions under only stretching conditions. This work [...] Read more.

The maximum force criteria and their derivatives, the Swift and Hill criteria, have been extensively used in the past to study sheet formability. Many extensions or modifications of these criteria have been proposed to improve necking predictions under only stretching conditions. This work analyses the maximum force principle under stretch-bending conditions and develops two different approaches to predict necking. The first is a generalisation of classical maximum force criteria to stretch-bending processes. The second approach is an extension of a previous work of the authors based on critical distance concepts, suggesting that necking of the sheet is controlled by the damage of a critical material volume located at the inner side of the sheet. An analytical deformation model is proposed to characterise the stretch-bending process under plane-strain conditions. Different parameters are considered, such as the thickness reduction, the gradient of variables through the sheet thickness, the thickness stress and the anisotropy of the material. The proposed necking models have been successfully applied to predict the failure in different materials, such as steel, brass and aluminium. Full article

(This article belongs to the Special Issue Advances in Plastic Forming of Metals)

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16 pages, 4562 KiB

Open AccessArticle

Effect of Grain Size on Grain Boundary Segregation Thermodynamics of Phosphorus in Interstitial-Free and 2.25Cr-1Mo Steels

by Yu Zhao¹, Shenhua Song^1,*, Hong Si² and Kai Wang^2,*

¹ Shenzhen Key Laboratory of Advanced Materials, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China

² Central Iron and Steel Research Institute, Beijing 100081, China

Metals 2017, 7(11), 470; https://doi.org/10.3390/met7110470 - 2 Nov 2017

Cited by 14 | Viewed by 6686

Abstract

Several grain sizes were obtained by heat treatment at different temperatures for interstitial-free (IF) and 2.25Cr-1Mo steels. Samples of the steels with different grain sizes were aged at 600 and 680 °C for IF steel and 520 and 560 °C for 2.25Cr-1Mo steel [...] Read more.

Several grain sizes were obtained by heat treatment at different temperatures for interstitial-free (IF) and 2.25Cr-1Mo steels. Samples of the steels with different grain sizes were aged at 600 and 680 °C for IF steel and 520 and 560 °C for 2.25Cr-1Mo steel for sufficient time to achieve their equilibrium grain boundary segregation. The grain boundary concentrations of phosphorus were examined using Auger electron spectroscopy. At the same aging temperature, the boundary segregation of phosphorus increased with increasing grain size. The effect of grain size on equilibrium grain boundary segregation thermodynamics was analyzed based on the information of both grain size and phosphorus boundary concentration. The segregation enthalpy increased with increasing grain size and simultaneously the segregation entropy became less negative. Moreover, the segregation entropy (∆S) and enthalpy (∆H) of phosphorus in both IF and 2.25Cr-1Mo steels exhibited a unified linear relationship, being expressed as ∆S = 0.85∆H − 38.06, although it segregated to different types of grain boundaries (ferrite grain boundaries in IF steel and prior austenite grain boundaries in 2.25Cr-1Mo steel). With the aid of the acquired thermodynamic parameters and grain boundary segregation theories, the equilibrium segregation concentrations at different aging temperatures were modeled under different grain sizes for both steels. Full article

(This article belongs to the Special Issue Physical Metallurgy of High Performance Steels)

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12 pages, 3716 KiB

Open AccessArticle

Effects of Vibration Amplitude on Microstructure Evolution and Mechanical Strength of Ultrasonic Spot Welded Cu/Al Joints

by Jian Liu¹, Biao Cao^1,* and Jingwei Yang²

¹ School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640, China

² School of Mechatronics Engineering, Foshan University, Foshan 52800, China

Metals 2017, 7(11), 471; https://doi.org/10.3390/met7110471 - 2 Nov 2017

Cited by 25 | Viewed by 5110

Abstract

The effects of vibration amplitude on the interface reaction and mechanical strength of the Cu/Al joints were systematically investigated in ultrasonic spot welding (USW) experiments. The appropriate vibration amplitude (22.5 μm) was beneficial for obtaining a sound joint. The formation of the continuous [...] Read more.

The effects of vibration amplitude on the interface reaction and mechanical strength of the Cu/Al joints were systematically investigated in ultrasonic spot welding (USW) experiments. The appropriate vibration amplitude (22.5 μm) was beneficial for obtaining a sound joint. The formation of the continuous intermetallic compounds (IMC) layer accelerated with a higher vibration amplitude. The lap shear tensile strength of the Cu/Al joints decreased when the thickness of the intermetallic layer was greater than 1 μm at various amplitudes. With the increase in welding time, a crack occurred in the copper side owing to the occurrence of the eutectic reaction,

α-A l + θ \to L

, at the periphery of the nugget. The remarkable decline of ultrasonic power curves occurred at various amplitude levels upon the formation of a crack in the copper side. Full article

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20 pages, 14010 KiB

Open AccessFeature PaperArticle

Evolution of Ternary AuAgPd Nanoparticles by the Control of Temperature, Thickness, and Tri-Layer

by Sundar Kunwar¹, Puran Pandey¹

, Mao Sui¹, Sushil Bastola¹ and Jihoon Lee^1,2,*

¹ College of Electronics and Information, Kwangwoon University, Seoul 01897, South Korea

² Institute of Nanoscale Science and Engineering, University of Arkansas, Fayetteville, AR 72701, USA

Metals 2017, 7(11), 472; https://doi.org/10.3390/met7110472 - 4 Nov 2017

Cited by 10 | Viewed by 6869

Abstract

Metallic alloy nanoparticles (NPs) possess great potential to enhance the optical, electronic, chemical, and magnetic properties for various applications by the control of morphology and elemental composition. This work presents the fabrication of ternary AuAgPd alloy nanostructures on sapphire (0001) via the solid-state [...] Read more.

Metallic alloy nanoparticles (NPs) possess great potential to enhance the optical, electronic, chemical, and magnetic properties for various applications by the control of morphology and elemental composition. This work presents the fabrication of ternary AuAgPd alloy nanostructures on sapphire (0001) via the solid-state dewetting of sputter-deposited tri-metallic layers. Based on the systematic control of temperature, thickness, and deposition order of tri-layers, the composite AuAgPd alloy nanoparticles (NPs) with various shape, size, and density are demonstrated. The metallic tri-layers exhibit various stages of dewetting based on the increasing growth temperatures between 400 and 900 °C at 15 nm tri-layer film thickness. Specifically, the nucleation of tiny voids and hillocks, void coalescence, the growth and isolated nanoparticle formation, and the shape transformation with Ag sublimation are observed. With the reduced film thickness (6 nm), tiny alloy NPs with improved structural uniformity and spatial arrangement are obtained due to enhanced dewetting. The growth trend of alloy NPs is drastically altered by changing the deposition order of metallic tri-layers. The overall evolution is governed by the surface diffusion and inter-mixing of metallic atoms, Rayleigh-like instability, surface and interface energy minimization, and equilibrium state of the system. The UV-VIS-NIR reflectance spectra reveal the formation of an absorption band and reflectance maxima at specific wavelengths based on the morphology and composition of AuAgPd alloy NPs. In addition, Raman spectra analysis shows the modulation of intensity and peak position of natural vibration modes of sapphire (0001). Full article

(This article belongs to the Special Issue Metallic Films: From Nanofabrication and Nanostructuration to Characterizations and Applications)

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12 pages, 3856 KiB

Open AccessArticle

Structure and Martensitic Transformation in Rapidly Solidified CoNiAlFe Alloy

by Huiling Chen¹, Jia Ju^1,2,3,*, Liguo Shuai^1,*, Huan Liu⁴

, Chen Yan⁵ and Zhuang Liu²

¹ School of Mechanical Engineering, Southeast University, Nanjing 211189, China

² Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology, School of Materials Engineering, Nanjing Institute of Technology, Nanjing 211167, China

³ Hangzhou Kaierda Electric Welder Co., Ltd., Hangzhou 310000, China

⁴ College of Mechanics and Materials, Hohai University, Nanjing 211100, China

⁵ Zhongtian Alloy Technology Co., Ltd., Nantong 226010, China

Metals 2017, 7(11), 473; https://doi.org/10.3390/met7110473 - 3 Nov 2017

Cited by 4 | Viewed by 4284

Abstract

Housler based magnetic controlled shape memory alloys are characterized by a large magnetic field induced strain. The strain was dependent on the twin martensite structure rearrangement, and the rapid solidification technology had a significant influence on the microstructure, physical, and chemical properties of [...] Read more.

Housler based magnetic controlled shape memory alloys are characterized by a large magnetic field induced strain. The strain was dependent on the twin martensite structure rearrangement, and the rapid solidification technology had a significant influence on the microstructure, physical, and chemical properties of the alloy. Thus, the structure and the martensitic transformation changes of Co₃₃Ni₃₁Al₂₇Fe₉ during the rapidly solidified process were studied. The microstructure of Co₃₃Ni₃₁Al₂₇Fe₉ with furnace cooled and rapid solidification (RS) constitutes a dual-phase structure, β phase and γ phase in a low cooling rate and martensite and γ phase in a high cooling rate. The γ phase at the grain boundaries reduced and became more fragile by raising the R_C value. The one-step austenite-martensite phase transformation occurred during the process of heating and cooling. The phase transition temperature presents an increasing trend by rising the cooling rate, even to over the room temperature. Moreover, the martensite structure in Co₃₃Ni₃₁Al₂₇Fe₉ constitutes a typical L1₀-type twinning structure. Full article

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22 pages, 8112 KiB

Open AccessFeature PaperArticle

Three-Dimensional Lattice Boltzmann Modeling of Dendritic Solidification under Forced and Natural Convection

by Mohsen Eshraghi^1,*, Mohammad Hashemi², Bohumir Jelinek³

and Sergio D. Felicelli^2,*

¹ Department of Mechanical Engineering, California State University Los Angeles, Los Angeles, CA 90032, USA

² Department of Mechanical Engineering, The University of Akron, Akron, OH 44325, USA

³ Center for Advanced Vehicular Systems, Mississippi State University, Starkville, MS 39759, USA

Metals 2017, 7(11), 474; https://doi.org/10.3390/met7110474 - 3 Nov 2017

Cited by 26 | Viewed by 6348

Abstract

A three-dimensional (3D) lattice Boltzmann (LB) model is developed to simulate the dendritic growth during solidification of Al-Cu alloys under forced and natural convection. The LB method is used to solve for solute diffusion and fluid flow. It is assumed that the dendritic [...] Read more.

A three-dimensional (3D) lattice Boltzmann (LB) model is developed to simulate the dendritic growth during solidification of Al-Cu alloys under forced and natural convection. The LB method is used to solve for solute diffusion and fluid flow. It is assumed that the dendritic growth is driven by the difference between the local actual and local equilibrium composition of the liquid in the interface. A cellular automaton (CA) scheme is adopted to capture new interface cells. The LB models for solute transport and fluid flow are first validated against two benchmark problems. The dendrite growth model is also validated with available analytical solutions. The evolution of a 3D dendrite affected by melt convection is investigated. Also, density inversion caused by solute concentration gradient is studied. It is shown that convection can change the kinetics of growth by affecting the solute distribution around the dendrite. In addition, the growth features of two-dimensional (2D) and 3D dendrites are briefly compared. The results show that decreasing undercooling and increasing solute concentration decelerates the growth in all branches of the dendrite. While increasing fluid velocity does not significantly influence upstream and transverse arms, it decreases the growth rate in the downstream direction considerably. The size ratio of the upstream arm to the downstream arm rises by increasing inlet velocity and solute content, and decreasing undercooling. Similarly, in the case of natural convection, redistribution of solute due to buoyancy-induced flow suppresses the growth of the upward arm and accelerates the growth of the downward arm. Considering the advantages offered by the LB method, the present model can be used as a new tool for simulating 3D dendritic solidification under convection. Full article

(This article belongs to the Special Issue Recent Advances in Study of Solid-Liquid Interfaces and Solidification of Metals)

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11 pages, 3458 KiB

Open AccessArticle

Thermally-Induced Crack Evaluation in H13 Tool Steel

by Hassan Abdulrssoul Abdulhadi^1,2,*, Syarifah Nur Aqida Syed Ahmad¹, Izwan Ismail³, Mahadzir Ishak¹ and Ghusoon Ridha Mohammed^1,2

¹ Faculty of Mechanical Engineering, University Malaysia Pahang, 26600 Pekan, Pahang, Malaysia

² Baghdad Institute, Middle Technical University, Baghdad 10074, Iraq

³ Faculty of Manufacturing Engineering, University Malaysia Pahang, 26600 Pekan, Pahanag, Malaysia

Metals 2017, 7(11), 475; https://doi.org/10.3390/met7110475 - 6 Nov 2017

Cited by 20 | Viewed by 6398

Abstract

This study reported the effect of thermal wear on cylindrical tool steel (AISI H13) under aluminum die-casting conditions. The AISIH13 steels were immersed in the molten aluminum alloy at 700 °C before water-quenching at room temperature. The process involved an alternating heating and [...] Read more.

This study reported the effect of thermal wear on cylindrical tool steel (AISI H13) under aluminum die-casting conditions. The AISIH13 steels were immersed in the molten aluminum alloy at 700 °C before water-quenching at room temperature. The process involved an alternating heating and cooling of each sample for a period of 24 s. The design of the immersion test apparatus stylistically simulated aluminum alloy dies casting conditions. The testing phase was performed at 1850, 3000, and 5000 cycles. The samples were subjected to visual inspection after each phase of testing, before being examined for metallographic studies, surface crack measurement, and hardness characteristics. Furthermore, the samples were segmented and examined under optical and Scanning Electron Microscopy (SEM). The areas around the crack zones were additionally examined under Energy Dispersive X-ray Spectroscopy (EDXS). The crack’s maximum length and Vickers hardness profiles were obtained; and from the metallographic study, an increase in the number of cycles during the testing phase resulted in an increase in the surface crack formation; suggesting an increase in the thermal stress at higher cycle numbers. The crack length of Region I (spherically shaped) was about 47 to 127 µm, with a high oxygen content that was analyzed within 140 µm from the surface of the sample. At 700 °C, there is a formation of aluminum oxides, which was in contact with the surface of the H13 sample. These stresses propagate the thermal wear crack length into the tool material of spherically shaped Region I and cylindrically shape Region II, while hardness parameters presented a different observation. The crack length of Region I was about 32% higher than the crack length of Region II. Full article

(This article belongs to the Special Issue Fatigue and Wear for Steels)

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15 pages, 14350 KiB

Open AccessFeature PaperArticle

In Situ Characterization of Inconel 718 Post-Dynamic Recrystallization within a Scanning Electron Microscope

by Meriem Zouari¹, Roland E. Logé^1,2 and Nathalie Bozzolo^1,*

¹ MINES ParisTech, PSL-Research University, CEMEF-Centre de Mise en Forme des matériaux, CNRS UMR 7635, CS 10207 rue Claude Daunesse, 06904 Sophia Antipolis CEDEX, France

² Thermomechanical Metallurgy Laboratory-PX Group Chair, Ecole Polytechnique Fédérale de Lausanne (EPFL), Rue de la Maladière 71B-CP 526, CH-2002 Neuchatel, Switzerland

Metals 2017, 7(11), 476; https://doi.org/10.3390/met7110476 - 4 Nov 2017

Cited by 39 | Viewed by 6042

Abstract

Microstructure evolution within the post-dynamic regime following hot deformation was investigated in Inconel 718 samples with different dynamically recrystallized volume fractions and under conditions such that no δ-phase particles were present. In situ annealing treatments carried out to mimic post-dynamic conditions inside the [...] Read more.

Microstructure evolution within the post-dynamic regime following hot deformation was investigated in Inconel 718 samples with different dynamically recrystallized volume fractions and under conditions such that no δ-phase particles were present. In situ annealing treatments carried out to mimic post-dynamic conditions inside the Scanning Electron Microscope (SEM) chamber suggest the occurrence of both metadynamic and static recrystallization mechanisms. Static recrystallization was observed in addition to metadynamic recrystallization, only when the initial dynamically recrystallized volume fraction was very small. The initial volume fraction of dynamically recrystallized grains appears to be decisive for subsequent microstructural evolution mechanisms and kinetics. In addition, the formation of annealing twins is observed along with the growth of recrystallized grains, but then the twin density decreases as the material enters the capillarity-driven grain growth regime. Full article

(This article belongs to the Special Issue Dynamic Recrystallization Behavior of Metallic Materials)

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15 pages, 7997 KiB

Open AccessArticle

Effect of Fly Ash Addition on the Physical and Mechanical Properties of AA6063 Alloy Reinforcement

by Alaa Mohammed Razzaq^1,2

, Dayang Laila Majid^1,*, Mohamad R. Ishak¹ and Uday M. Basheer^3,4

¹ Department of Aerospace Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor Darul Ehsan, Malaysia

² Oil Products Distribution Company, Iraq Ministry of Oil, 10022 Al Doura, Baghdad, Iraq

³ Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia

⁴ UTM Centre for Low Carbon Transport in Cooperation with Imperial College London, Institute for Vehicle Systems and Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Malaysia

Metals 2017, 7(11), 477; https://doi.org/10.3390/met7110477 - 4 Nov 2017

Cited by 73 | Viewed by 7394

Abstract

Aluminum-fly ash particulate-reinforced composites (AA6063-FA) have been used in various engineering fields, such as automotive and aerospace industries, due to their low density and good mechanical properties. There are many fabrication techniques available to manufacture these composites according to matrix and reinforcement materials. [...] Read more.

Aluminum-fly ash particulate-reinforced composites (AA6063-FA) have been used in various engineering fields, such as automotive and aerospace industries, due to their low density and good mechanical properties. There are many fabrication techniques available to manufacture these composites according to matrix and reinforcement materials. The compocasting technique for the fabrication of the AA6063 matrix composite reinforced with fly ash particles is the focus of this research. Fly ash content was in the range of 0–12 wt % in increasing increments of 2%. Fly ash particles were added to the molten AA6063 alloy until they were completely blended and cooled down just below the liquidus to keep the slurry in the semi-solid state. After this, the molten AA6063-FA composites were cast into prepared cast iron molds. Bulk density and apparent porosity measurements, Charpy impact testing, Vickers microhardness measurements, Field Emission Scanning Electron Microscope (FESEM), Variable Pressure Scanning Electron Microscope and Energy Dispersive X-ray spectroscope (EDS) elemental mapping were used to evaluate these materials. The results showed that an increase in the fly ash content in the melted leads results in an increase in the microhardness and porosity in the composites. In contrast, the bulk density and Charpy impact energy of the composites decreased with an increase in the fly ash content. Full article

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14 pages, 3336 KiB

Open AccessFeature PaperArticle

Microstructure Formation and Resistivity Change in CuCr during Rapid Solidification

by Ulla Hauf^1,*, Alexander Kauffmann¹, Sandra Kauffmann-Weiss², Alexander Feilbach³, Mike Boening⁴, Frank E. H. Mueller⁴, Volker Hinrichsen³ and Martin Heilmaier¹

¹ Institute for Applied Materials (IAM-WK), Karlsruhe Institute of Technology (KIT), Engelbert-Arnold-Straße 4, 76131 Karlsruhe, Germany

² Institute for Technical Physics (ITEP), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany

³ High Voltage Laboratories (HST), Technische Universität Darmstadt, Fraunhoferstr. 4, 64283 Darmstadt, Germany

⁴ Plansee Powertech AG, Retterswil 13, 5703 Seon, Switzerland

Metals 2017, 7(11), 478; https://doi.org/10.3390/met7110478 - 4 Nov 2017

Cited by 14 | Viewed by 5223

Abstract

The formation of the surface-near microstructure after a current interruption of CuCr contact materials in a vacuum interrupter is characterized by a fast heating and subsequently rapid solidification process. In the present article, we reveal and analyse the formation of two distinct microstructural [...] Read more.

The formation of the surface-near microstructure after a current interruption of CuCr contact materials in a vacuum interrupter is characterized by a fast heating and subsequently rapid solidification process. In the present article, we reveal and analyse the formation of two distinct microstructural regions that result from the heat, which is generated and dissipated during interruption. In the topmost region, local and global texture, as well as the resulting microstructure, indicate that both Cu and Cr were melted during rapid heating and solidification whereas in the region underneath, only Cu was melted and elongated Cu-grains solidified with the <001>-direction perpendicularly aligned to the surface. By analysing the lattice parameter of the Cu solid solution, a supersaturation of the solid solution with about 2.25 at % Cr was found independent if Cu was melted solely or together with the Cr. The according reduction of electrical conductivity in the topmost region subsequent to current interruption and the resulting heat distribution are discussed based on these experimental results. Full article

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9 pages, 1191 KiB

Open AccessArticle

A Method to Determine the Electrical Resistance of a Metallic Powder Mass under Compression

by Juan Manuel Montes¹

, Francisco Gómez Cuevas²

, Fátima Ternero^1,*

, Raquel Astacio¹, Eduardo Sánchez Caballero¹

and Jesús Cintas¹

¹ Metallurgy and Materials Engineering Group, Escuela Técnica Superior de Ingeniería, Universidad de Sevilla, Camino de los Descubrimientos s/n, 41092 Sevilla, Spain

² Department of Chemical Engineering, Physical Chemistry and Materials Science, Escuela Técnica Superior de Ingeniería, Universidad de Huelva, Campus El Carmen, Avda. Tres de Marzo s/n, 21007 Huelva, Spain

Metals 2017, 7(11), 479; https://doi.org/10.3390/met7110479 - 6 Nov 2017

Cited by 17 | Viewed by 5289

Abstract

In this paper, a phenomenological model to predict the value of the electrical resistance of a compressed metal powder mass is proposed. The model, based on the experimental compressibility and resistivity-porosity curves, is useful in the field of the electrical resistance consolidation. In [...] Read more.

In this paper, a phenomenological model to predict the value of the electrical resistance of a compressed metal powder mass is proposed. The model, based on the experimental compressibility and resistivity-porosity curves, is useful in the field of the electrical resistance consolidation. In this area is often required to find out whether a certain mass of powder inside a die of specified inner section, and subjected to a certain compression, reaches a sufficiently small resistance value so that it can be consolidated by electrical means. The model also predicts the electrical resistance value of the powder mass in case of powders with no oxide layers, or after removing them mechanically or electrically by a previous activation process. The model predictions have been successfully validated through direct measurements of electrical resistance in powder aggregates both in as-received state and after electrical activation. Full article

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14 pages, 6536 KiB

Open AccessFeature PaperArticle

Anisotropic Hardening Behaviour and Springback of Advanced High-Strength Steels

by Jaebong Jung¹

, Sungwook Jun¹, Hyun-Seok Lee², Byung-Min Kim¹, Myoung-Gyu Lee³ and Ji Hoon Kim^1,*

¹ School of Mechanical Engineering, Pusan National University, Busan 46241, Korea

² NARA Mold & Die Co., Ltd., Changwon 51555, Korea

³ Department of Materials Science and Engineering, Korea University, Seoul 02841, Korea

Metals 2017, 7(11), 480; https://doi.org/10.3390/met7110480 - 6 Nov 2017

Cited by 28 | Viewed by 8628

Abstract

Advanced high-strength steels (AHSSs) exhibit large, and sometimes anisotropic, springback recovery after forming. Accurate description of the anisotropic elasto-plastic behaviour of sheet metals is critical for predicting their anisotropic springback behaviour. For some materials, the initial anisotropy is maintained while hardening progresses. However, [...] Read more.

Advanced high-strength steels (AHSSs) exhibit large, and sometimes anisotropic, springback recovery after forming. Accurate description of the anisotropic elasto-plastic behaviour of sheet metals is critical for predicting their anisotropic springback behaviour. For some materials, the initial anisotropy is maintained while hardening progresses. However, for other materials, anisotropy changes with hardening. In this work, to account for the evolution of anisotropy of a dual-phase steel, an elastoplastic material constitutive model is developed. In particular, the combined isotropic–kinematic hardening model was modified. Tensile loading–unloading, uniaxial and biaxial tension, and tension–compression tests were conducted along the rolling, diagonal, and transverse directions to measure the anisotropic properties, and the parameters of the proposed constitutive model were determined. For validation, the proposed model was applied to a U-bending process, and the measured springback angles were compared to the predicted ones. Full article

(This article belongs to the Special Issue Advances in Plastic Forming of Metals)

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18 pages, 14433 KiB

Open AccessArticle

Development of a Novel Degradation-Controlled Magnesium-Based Regeneration Membrane for Future Guided Bone Regeneration (GBR) Therapy

by Da-Jun Lin¹, Fei-Yi Hung^1,*

, Hung-Pang Lee² and Ming-Long Yeh^2,*

¹ Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan

² Department of Biomedical Engineering, National Cheng Kung University, Tainan 701, Taiwan

Metals 2017, 7(11), 481; https://doi.org/10.3390/met7110481 - 6 Nov 2017

Cited by 18 | Viewed by 6943

Abstract

This study aimed to develop and evaluate the ECO-friendly Mg-5Zn-0.5Zr (ECO505) alloy for application in dental-guided bone regeneration (GBR). The microstructure and surface properties of biomedical Mg materials greatly influence anti-corrosion performance and biocompatibility. Accordingly, for the purpose of microstructure and surface modification, [...] Read more.

This study aimed to develop and evaluate the ECO-friendly Mg-5Zn-0.5Zr (ECO505) alloy for application in dental-guided bone regeneration (GBR). The microstructure and surface properties of biomedical Mg materials greatly influence anti-corrosion performance and biocompatibility. Accordingly, for the purpose of microstructure and surface modification, heat treatments and surface coatings were chosen to provide varied functional characteristics. We developed and integrated both an optimized solution heat-treatment condition and surface fluoride coating technique to fabricate a Mg-based regeneration membrane. The heat-treated Mg regeneration membrane (ARRm-H380) and duplex-treated regeneration membrane group (ARRm-H380-F24 h) were thoroughly investigated to characterize the mechanical properties, as well as the in vitro corrosion and in vivo degradation behaviors. Significant enhancement in ductility and corrosion resistance for the ARRm-H380 was obtained through the optimized solid-solution heat treatment; meanwhile, the corrosion resistance of ARRm-H380-F24 h showed further improvement, resulting in superior substrate integrity. In addition, the ARRm-H380 provided the proper amount of Mg-ion concentration to accelerate bone growth in the early stage (more than 80% new bone formation). From a specific biomedical application point of view, these research results point out a successful manufacturing route and suggest that the heat treatment and duplex treatment could be employed to offer custom functional regeneration membranes for different clinical patients. Full article

(This article belongs to the Special Issue Biodegradable Metals)

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15 pages, 12348 KiB

Open AccessArticle

Effects of Short-Range Order on the Magnetic and Mechanical Properties of FeCoNi(AlSi)_x High Entropy Alloys

by Wenqiang Feng^1,2,3,*

, Yang Qi⁴ and Shaoqing Wang¹

¹ Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

² College of Science, University of Science and Technology Liaoning, Anshan 114051, China

³ University of Chinese Academy of Sciences, Beijing 100049, China

⁴ College of Science, Northeastern University, Shenyang 110819, China

Metals 2017, 7(11), 482; https://doi.org/10.3390/met7110482 - 6 Nov 2017

Cited by 67 | Viewed by 8890

Abstract

The properties of a material are sensitive to chemically-ordered structure in multi-element alloys. Understanding the effects of chemical short-range order (SRO) on magnetic and mechanical properties is important. In this work, we use the Monte Carlo method in combination with density functional theory [...] Read more.

The properties of a material are sensitive to chemically-ordered structure in multi-element alloys. Understanding the effects of chemical short-range order (SRO) on magnetic and mechanical properties is important. In this work, we use the Monte Carlo method in combination with density functional theory to investigate atomic nearest neighbor distribution, magnetic moment and elastic modulus in FeCoNi (AlSi)_x alloys. It is found that the prominent feature of the FeCoNi (AlSi)_x alloys is the change of SRO parameters: the SRO parameters are positive between Al-Al, Al-Si, Si-Si pairs and negative between Ni-Al, Co-Si, Fe-Co, Ni-Si and Fe-Si pairs. The Al and Si elements tend to bond with Fe, Co, Ni elements to form an SRO structure. The change of the atomic nearest neighbor environment leads to a reduction in the atomic magnetic moments of magnetic elements. The calculated saturation magnetizations by considering the effect of SRO are in good accord with the experimental values. We further show that SRO leads to an increase of the elastic modulus, by sacrificing ductility and isotropy. In the study of the structure and properties of high entropy alloys, the effect of SRO should not be ignored. Full article

(This article belongs to the Special Issue Microstructure based Modeling of Metallic Materials)

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13 pages, 7777 KiB

Open AccessArticle

Numerical Study on Solidification Behavior and Structure of Continuously Cast U71Mn Steel

by Qing Fang

, Hongwei Ni^*, Hua Zhang, Bao Wang and Chengsong Liu

The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China

Metals 2017, 7(11), 483; https://doi.org/10.3390/met7110483 - 7 Nov 2017

Cited by 19 | Viewed by 4441

Abstract

The solidification behavior and structure of continuous casting high rail U71Mn bloom, under different secondary cooling conditions and superheat, were numerically investigated using the Cellular Automaton-Finite Element (CAFE) model implemented with ProCAST software. Nail shooting and macro etch experiments of the bloom samples [...] Read more.

The solidification behavior and structure of continuous casting high rail U71Mn bloom, under different secondary cooling conditions and superheat, were numerically investigated using the Cellular Automaton-Finite Element (CAFE) model implemented with ProCAST software. Nail shooting and macro etch experiments of the bloom samples under different cooling conditions were conducted to verify the model of macroscopic solidification and structure. The results showed that the simulated results of the solidified shell and solidification structure are basically consistent with experimental results. The secondary cooling condition has little effect on the grain size and distribution of the bloom, while both the bloom surface and corner temperatures are higher and the temperature rise at the beginning of the air-cooling zone is smaller under the super-slow cooling condition. The percentage of center-equiaxed grains decreases from 44.6% to 20.1% and the grain average radius increases from 1.025 to 1.128 mm when the superheat increases from 15 to 40 K, with little change in the grain size occurring between 15 and 20 K. Moreover, for a step increase in the superheat of 5 K, the solidification end is lengthened by about 0.19 m and the surface temperature is enhanced by 3 K. The super-slow secondary cooling condition with the superheat controlled within 20 K is suitable for big-bloom casting. Full article

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15 pages, 7837 KiB

Open AccessArticle

Experimental Investigation of Forming Forces in Frictional Stir Incremental Forming of Aluminum Alloy AA6061-T6

by B.T.H.T. Baharudin^1,2,*

, Q.M. Azpen^1,3, Shamsuddin Sulaima^1,2 and F. Mustapha⁴

¹ Department of Mechanical & Manufacturing Engineering, Faculty of Engineering, Universiti Putra Malaysia, Serdang 43400, Malaysia

² Advanced Manufacturing Research Centre, Department of Mechanical & Manufacturing Engineering, Faculty of Engineering, Universiti Putra Malaysia, Serdang 43400, Malaysia

³ Middle Technical University-Institute of Technology, Baghdad 10001, Iraq

⁴ Department of Aerospace Engineering, Faculty of Engineering, University Putra Malaysia, Serdang 43400, Malaysia

Metals 2017, 7(11), 484; https://doi.org/10.3390/met7110484 - 7 Nov 2017

Cited by 30 | Viewed by 8001

Abstract

The incremental sheet forming (ISF) process is an emerging flexible sheet-forming process, which is adequate for the manufacturing of unique or small-volume batches. Single-point incremental forming (SPIF) is the original technology of incremental sheet-forming processes. In this article, frictional stir-assisted SPIF was used [...] Read more.

The incremental sheet forming (ISF) process is an emerging flexible sheet-forming process, which is adequate for the manufacturing of unique or small-volume batches. Single-point incremental forming (SPIF) is the original technology of incremental sheet-forming processes. In this article, frictional stir-assisted SPIF was used to deform AA6061-T6 aluminum alloy. Experimental tests were conducted to measure the forming forces during this process for the concerned lightweight material. The influence of process parameters was investigated, which included tool rotation speed, feed rate, step size and tool diameter on the produced forming forces. A Taguchi technique for the design of experiment (DOE) and the varying wall angle conical frustum (VWACF) test was employed in this study. The results show that the rotation spindle speed was the most dominant parameter that affects the forming forces, followed by the step size, feed rate and tool diameter. In addition, the interaction between the feed rate and step size has a notable impact on the values of the forming forces. Full article

(This article belongs to the Special Issue Metallic Materials and Manufacturing)

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7 pages, 10483 KiB

Open AccessCommunication

Rapid Degradation of Azo Dyes by Melt-Spun Mg-Zn-Ca Metallic Glass in Artificial Seawater

by Peng Chen, Ximei Hu, Yumin Qi, Xin Wang^*

, Zongjia Li, Lichen Zhao, Shuiqing Liu and Chunxiang Cui^*

Key Laboratory for New Type of Functional Materials in Hebei Province, School of Material Science and Engineering, Hebei University of Technology, Tianjin 300130, China

Metals 2017, 7(11), 485; https://doi.org/10.3390/met7110485 - 8 Nov 2017

Cited by 18 | Viewed by 4078

Abstract

Mg-Zn-Ca metallic glass (MG) is effective for degrading azo dyes; however, the related surface evolution and degradation mechanisms are little known. We comparatively investigated the initial surface corrosion morphologies of melt-spun Mg₆₆Zn₃₀Ca₄ MG in deionized water and artificial [...] Read more.

Mg-Zn-Ca metallic glass (MG) is effective for degrading azo dyes; however, the related surface evolution and degradation mechanisms are little known. We comparatively investigated the initial surface corrosion morphologies of melt-spun Mg₆₆Zn₃₀Ca₄ MG in deionized water and artificial seawater. It was found that the basic corrosion behavior of the MG was the same, except that the corrosion process was accelerated in seawater. The presence of NaCl obviously promotes the formation of nano-ZnO on the surface of ribbons, causing the rapid degradation of azo dyes due to the photocatalytic effect. The degradation efficiency when combined with 3.5 wt % NaCl was over 100 times higher than that without NaCl. This indicates that Mg-Zn-Ca MG ribbons are effective additives for the degradation of azo dyes in seawater. Full article

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15 pages, 2436 KiB

Open AccessArticle

An Investigation of the Micro-Electrical Discharge Machining of Nickel-Titanium Shape Memory Alloy Using Grey Relations Coupled with Principal Component Analysis

by Mustufa Haider Abidi^1,*

, Abdulrahman M. Al-Ahmari^1,2, Arshad Noor Siddiquee³

, Syed Hammad Mian¹

, Muneer Khan Mohammed¹ and Mohammed Sarvar Rasheed⁴

¹ Princess Fatima Alnijiris Research Chair for Advanced Manufacturing Technology (FARCAMT Chair), Advanced Manufacturing Institute, King Saud University, Riyadh 11421, Saudi Arabia

² Industrial Engineering Department, College of Engineering, King Saud University, Riyadh 11421, Saudi Arabia

³ Department of Mechanical Engineering, Jamia Millia Islamia (A Central University), New Delhi 110025, India

⁴ Academics Department, Baynounah Institute of Science and Technology, Adveti, Madinat Zayed 57788, UAE

Metals 2017, 7(11), 486; https://doi.org/10.3390/met7110486 - 9 Nov 2017

Cited by 37 | Viewed by 6256

Abstract

Shape memory alloys (SMAs) are advanced engineering materials which possess shape memory effects and super-elastic properties. Their high strength, high wear-resistance, pseudo plasticity, etc., makes the machining of Ni-Ti based SMAs difficult using traditional techniques. Among all non-conventional processes, micro-electric discharge machining (micro-EDM) [...] Read more.

Shape memory alloys (SMAs) are advanced engineering materials which possess shape memory effects and super-elastic properties. Their high strength, high wear-resistance, pseudo plasticity, etc., makes the machining of Ni-Ti based SMAs difficult using traditional techniques. Among all non-conventional processes, micro-electric discharge machining (micro-EDM) is considered one of the leading processes for micro-machining, owing to its high aspect ratio and capability to machine hard-to-cut materials with good surface finish.The selection of the most appropriate input parameter combination to provide the optimum values for various responses is very important in micro-EDM. This article demonstrates the methodology for optimizing multiple quality characteristics (overcut, taper angle and surface roughness) to enhance the quality of micro-holes in Ni-Ti based alloy, using the Grey–Taguchi method. A Taguchi-based grey relational analysis coupled with principal component analysis (Grey-PCA) methodology was implemented to investigate the effect of three important micro-EDM process parameters, namely capacitance, voltage and electrode material.The analysis of the individual responses established the importance of multi-response optimization. The main effects plots for the micro-EDM parameters and Analysis of Variance (ANOVA) indicate that every parameter does not produce same effect on individual responses, and also that the percent contribution of each parameter to individual response is highly varied. As a result, multi-response optimization was implemented using Grey-PCA. Further, this study revealed that the electrode material had the strongest effect on the multi-response parameter, followed by the voltage and capacitance. The main effects plot for the Grey-PCA shows that the micro-EDM parameters “capacitance” at level-2 (i.e., 475 pF), “discharge voltage” at level-1 (i.e., 80 V) and the “electrode material” Cu provided the best multi-response. Full article

(This article belongs to the Special Issue Machining and Finishing of Nickel and Titanium Alloys)

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11 pages, 8519 KiB

Open AccessArticle

Evaluation of Surface Mechanical Properties and Grindability of Binary Ti Alloys Containing 5 wt % Al, Cr, Sn, and V

by Hae-Soon Lim^1,2, Moon-Jin Hwang³, Ha-Na Jeong², Woon-Young Lee³, Ho-Jun Song³ and Yeong-Joon Park^3,*

¹ Department of Dental Education, School of Dentistry, Chonnam National University, Gwangju 61186, Korea

² Department of Dentistry, Chonnam National University Hwasun Hospital, Hwasun-gun, Jeonnam 58128, Korea

³ Department of Dental Materials and Medical Research Center for Biomineralization Disorders, School of Dentistry, Chonnam National University, Gwangju 61186, Korea

Metals 2017, 7(11), 487; https://doi.org/10.3390/met7110487 - 9 Nov 2017

Cited by 11 | Viewed by 4014

Abstract

This study aimed to investigate the relationship between the surface mechanical properties and the grindability of Ti alloys. Binary Ti alloys containing 5 wt % concentrations of Al, Cr, Sn, or V were prepared using a vacuum arc melting furnace, and their surface [...] Read more.

This study aimed to investigate the relationship between the surface mechanical properties and the grindability of Ti alloys. Binary Ti alloys containing 5 wt % concentrations of Al, Cr, Sn, or V were prepared using a vacuum arc melting furnace, and their surface properties and grindability were compared to those of commercially pure Ti (cp-Ti). Ti alloys containing Al and Sn had microstructures that consisted of only α phase, while Ti alloys containing Cr and V had lamellar microstructures that consisted of α + β phases. The Vickers microhardness of Ti alloys was increased compared to those of cp-Ti by the solid solution strengthening effect. Among Ti alloys, Ti alloy containing Al had the highest Vickers microhardness. At a low SiC wheel speed of 5000 rpm, the grinding rates of Ti alloys showed an increasing tendency as the hardness values of Ti alloys decreased. At a high SiC wheel speed of 10,000 rpm, the grinding rates of Ti alloys showed an increasing tendency as the tensile strength values increased. The Ti alloy containing Al, which showed the lowest tensile strength, had the lowest grinding rate. The grinding ratios of the Ti alloys were higher than those of cp-Ti at both wheel revolution speeds of 5000 and 10,000 rpm. The grinding ratio of the Ti alloy containing Al was significantly increased at 10,000 rpm (p < 0.05). Full article

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13 pages, 3257 KiB

Open AccessFeature PaperArticle

Inhibition of Brass (80/20) by 5-Mercaptopentyl-3-Amino-1,2,4-Triazole in Neutral Solutions

by Ivan А. Arkhipushkin^1,2, Khidmet S. Shikhaliev³, Andrei Y. Potapov³

, Lyudmila V. Sapronova⁴ and Leonid P. Kazansky^2,*

¹ Department of Chemical Enginering, Dmitry Mendeleev Russian Chemical Technology University, 9 Miusskaya sq., 125047 Moscow, Russia

² Laboratory of Physico-chemical Fundamentals of Corrosion Inhibition of Metals and Alloys, Russian Academy of Sciences (RAS), A.N. Frumkin Institute of Physical Chemistry and Electrochemistry (IPCE RAS), 31 Leninski prospect, 119071 Moscow, Russia

³ Department of Organic Chemistry, Voronezh State University, 1 Universitetskaya sq., 394006 Voronezh, Russia

⁴ Department of Organic Chemistry, Peoples’ Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya st., 117198 Moscow, Russia

Metals 2017, 7(11), 488; https://doi.org/10.3390/met7110488 - 9 Nov 2017

Cited by 20 | Viewed by 7873

Abstract

The effect of the adsorption of 5-mercaptopentyl-3-amino-1,2,4-triazole (MPATA) on the corrosive behavior of brass (Cu80/Zn20) in neutral (pH 7.4) borate buffer solutions with and without 0.01 M NaCl was studied. Electrochemical methods show significant decrease of the anodic and cathodic currents on the [...] Read more.

The effect of the adsorption of 5-mercaptopentyl-3-amino-1,2,4-triazole (MPATA) on the corrosive behavior of brass (Cu80/Zn20) in neutral (pH 7.4) borate buffer solutions with and without 0.01 M NaCl was studied. Electrochemical methods show significant decrease of the anodic and cathodic currents on the polarization curves in the presence of MPATA. X-ray photoelectron spectroscopy (XPS) reveals MPATA adsorption on the brass surface from an inhibitor solution. After 17 h of exposure, a mixed complex [Cu_xZn_yMPATA_z] with a thickness of about 3–3.5 nm is formed on the surface. This nanolayer has sufficient protective ability to withstand corrosion tests in a salt fog chamber: after 5 days of testing, the samples remain glossy and less than 1% of the surface has been damaged. After corrosion tests in a salt fog chamber, the surface of unprotected samples is enriched with zinc, while at the surface of inhibitor-treated samples, the copper and zinc are present in practically equal contents. Full article

(This article belongs to the Special Issue Corrosion Inhibition)

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9 pages, 4397 KiB

Open AccessArticle

Revisiting Mg–Mg₂Ni System from Electronic Perspective

by Zhao Qian^1,*

, Weimin Guo²

, Guanzhong Jiang¹, Shaokun Xu¹, Rajeev Ahuja^3,4

and Xiangfa Liu¹

¹ Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (Ministry of Education), Shandong University, Jinan 250061, China; Suzhou Institute of Shandong University, Suzhou 215000, China

² Key Laboratory of Applied Technology of Sophisticated Analytical Instruments, Shandong Academy of Sciences, Jinan 250014, China

³ Condensed Matter Theory, Department of Physics and Astronomy, Ångström Laboratory, Uppsala University, SE-752 37 Uppsala, Sweden

⁴ Department of Materials Science and Engineering, KTH Royal Institute of Technology, S-100 44 Stockholm, Sweden

Metals 2017, 7(11), 489; https://doi.org/10.3390/met7110489 - 9 Nov 2017

Cited by 5 | Viewed by 4533

Abstract

Both Mg and Mg₂Ni are promising electrode materials in conversion-type secondary batteries. Earlier studies have shown their single-phase prospects in electro-devices, while in this work, we have quantitatively reported the electronic properties of their dual-phase materials, that is, Mg–Mg₂Ni [...] Read more.

Both Mg and Mg₂Ni are promising electrode materials in conversion-type secondary batteries. Earlier studies have shown their single-phase prospects in electro-devices, while in this work, we have quantitatively reported the electronic properties of their dual-phase materials, that is, Mg–Mg₂Ni alloys, and analyzed the underlying reasons behind the property changes of materials. The hypoeutectic Mg–Mg₂Ni alloys are found to be evidently more conductive than the hypereutectic Mg–Mg₂Ni system. The density functional theory (DFT) calculations give the intrinsic origin of electronic structures of both Mg₂Ni and Mg. The morphology of quasi-nanoscale eutectics is another factor that can affect the electronic properties of the investigated alloy system; that is, the electrical property change of the investigated alloys system is due to a combination of the intrinsic property difference between the two constituting phases and the change of eutectic microstructures that affect electron scattering. In addition, regarding the Mg–Mg₂Ni alloy design for device applications, the electronic property and mechanical aspect should be well balanced. Full article

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15 pages, 11861 KiB

Open AccessArticle

Effect of Dynamic Reheating Induced by Weaving on the Microstructure of GTAW Weld Metal of 25% Cr Super Duplex Stainless Steel Weld Metal

by Hee-Joon Sung¹, Hye-Sung Na² and Chung-Yun Kang^2,*

¹ Department of Hybrid Materials & Machining Technology, Graduate School of Convergence Science, Pusan National University, Busan 46241, Korea

² Department of Material Science and Engineering, Pusan National University, Busandaehak-ro 63 beon-gil, Geumjeong-gu, Busan 46241, Korea

Metals 2017, 7(11), 490; https://doi.org/10.3390/met7110490 - 9 Nov 2017

Cited by 4 | Viewed by 6265

Abstract

The importance of the additional growth and/or transformation of the austenite phase that occurs in weld metals of super duplex stainless steel upon reheating is known. However, the effects have not been fully investigated, especially with respect to reheating induced by weaving during [...] Read more.

The importance of the additional growth and/or transformation of the austenite phase that occurs in weld metals of super duplex stainless steel upon reheating is known. However, the effects have not been fully investigated, especially with respect to reheating induced by weaving during single-pass welding. In this work, bead-on-pipe gas tungsten arc welding (GTAW) was conducted on super duplex stainless steel to understand the effect of weaving on the microstructure of weld metal. Microstructural analysis, electron backscatter diffraction (EBSD), and focused ion beam transmission electron microscopy (FIB-TEM) were carried out to investigate the relationship between weaving and microstructural change. The weaving of GTAW produced a dynamic reheated area just before the weld bead during welding. It was revealed that extensive reheated weld existed even after one welding pass, and that the content of the austenite phase in the reheated area was higher than that in the non-reheated area, indicating the existence of a large quantity of intragranular austenite phase. In addition, the Cr₂N content in the reheated area was lower than that in the non-reheated area. This reduction of Cr₂N was closely related to the reheating resulting from weaving. TEM analysis revealed that Cr₂N in the non-reheated area was dispersed following heating and transformed to secondary austenite. Full article

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14 pages, 4354 KiB

Open AccessArticle

Experimental Validation of an FSW Model with an Enhanced Friction Law: Application to a Threaded Cylindrical Pin Tool

by Narges Dialami^1,*

, Miguel Cervera¹

, Michele Chiumenti¹

, Antonio Segatori² and Wojciech Osikowicz²

¹ International Center for Numerical Methods in Engineering (CIMNE), Universidad Politécnica de Cataluña, Campus Norte UPC, 08034 Barcelona, Spain

² Sapa AB Technology, Kanalgatan 1, 612 81 Finspang, Sweden

Metals 2017, 7(11), 491; https://doi.org/10.3390/met7110491 - 10 Nov 2017

Cited by 17 | Viewed by 5013

Abstract

This work adopts a fast and accurate two-stage computational strategy for the analysis of FSW (Friction stir welding) processes using threaded cylindrical pin tools. The coupled thermo-mechanical problem is equipped with an enhanced friction model to include the effect of non-uniform pressure distribution [...] Read more.

This work adopts a fast and accurate two-stage computational strategy for the analysis of FSW (Friction stir welding) processes using threaded cylindrical pin tools. The coupled thermo-mechanical problem is equipped with an enhanced friction model to include the effect of non-uniform pressure distribution under the pin shoulder. The overall numerical strategy is successfully validated by the experimental measurements provided by the industrial partner (Sapa). The verification of the numerical model using the experimental evidence is not only accomplished in terms of temperature evolution but also in terms of torque, longitudinal, transversal and vertical forces. Full article

(This article belongs to the Special Issue Recent Achievements in Rotary, Linear and Friction Stir Welding of Metals Alloys)

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19 pages, 20713 KiB

Open AccessArticle

Microstructures and Mechanical Properties of Dissimilar Al/Steel Butt Joints Produced by Autogenous Laser Keyhole Welding

by Li Cui^1,*, Boxu Chen¹, Wei Qian¹, Dingyong He¹ and Li Chen²

¹ College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China

² High Energy Density Beam Processing Technology Department, Aeronautical Manufacturing Technology Research Institute, Beijing 100024, China

Metals 2017, 7(11), 492; https://doi.org/10.3390/met7110492 - 10 Nov 2017

Cited by 32 | Viewed by 6981

Abstract

Dissimilar Al/steel butt joints of 6.0 mm thick plates have been achieved using fiber laser keyhole welding autogenously. The cross sections, interface microstructures, hardness and tensile properties of Al/steel butt joints obtained under different travel speeds and laser beam offsets were investigated. The [...] Read more.

Dissimilar Al/steel butt joints of 6.0 mm thick plates have been achieved using fiber laser keyhole welding autogenously. The cross sections, interface microstructures, hardness and tensile properties of Al/steel butt joints obtained under different travel speeds and laser beam offsets were investigated. The phase morphology and thickness of the intermetallic compound (IMC) layers at the interface were analyzed by scanning electronic microscopes (SEM) using the energy-dispersive spectrometry (EDS) and electron back-scattered diffraction (EBSD) techniques. The results show that travel speeds and laser beam offsets are of considerable importance for the weld shape, morphology and thickness of IMC layers, and ultimate tensile strength (UTS) of Al/steel butt joints. This proves that the IMC layers consist of Fe₂Al₅ phases and Fe₄Al₁₃ phases by EBSD phase mapping. Increasing laser beam offsets from 0.3 mm to 0.7 mm significantly decreases the quantity of Fe₄Al₁₃ phases and the thickness of Fe₂Al₅ layers at the interface. During tensile processing, the Fe₂Al₅ layer with the weakest bonding strength is the most brittle region at the interface. However, an intergranular fracture that occurred at Fe₂Al₅ layers leads to a relatively high UTS of Al/steel butt joints. Full article

(This article belongs to the Special Issue Laser Welding)

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8 pages, 1404 KiB

Open AccessArticle

Effect of Hydrogen on the Elastic and Anelastic Properties of the R Phase in Ti₅₀Ni_46.1Fe_3.9 Alloy

by Konstantin Sapozhnikov^1,2,*

, Joan Torrens-Serra³, Eduard Cesari³

, Jan Van Humbeeck⁴ and Sergey Kustov^2,3

¹ Division of Solid State Physics, Ioffe Institute, Politekhnicheskaya 26, 194021 St. Petersburg, Russia

² Department of Modern Functional Materials, ITMO University, Kronverkskiy 49, 197101 St. Petersburg, Russia

³ Departament de Física, Universitat de les Illes Balears, Cra Valldemossa km 7.5, E 07122 Palma de Mallorca, Spain

⁴ Departement Materiaalkunde (MTM), Katholieke Universiteit Leuven, Kasteelpark Arenberg 44, B-3001 Leuven, Belgium

Metals 2017, 7(11), 493; https://doi.org/10.3390/met7110493 - 10 Nov 2017

Cited by 3 | Viewed by 3672

Abstract

The linear and non-linear internal friction, effective Young’s modulus, and amplitude-dependent modulus defect of a Ti₅₀Ni_46.1Fe_3.9 alloy have been studied after different heat treatments, affecting hydrogen content, at temperatures of 13–300 K, and frequencies near 90 kHz. It [...] Read more.

The linear and non-linear internal friction, effective Young’s modulus, and amplitude-dependent modulus defect of a Ti₅₀Ni_46.1Fe_3.9 alloy have been studied after different heat treatments, affecting hydrogen content, at temperatures of 13–300 K, and frequencies near 90 kHz. It has been shown that the contamination of the alloy by hydrogen gives rise to an internal friction maximum in the R martensitic phase and a complicated pinning stage in the temperature dependence of the effective Young’s modulus at temperatures corresponding to the high-temperature side of the maximum. Dehydrogenation of the H-contaminated alloy transforms the internal friction maximum into a plateau and minimizes the pinning stage. The internal friction maximum is associated with a competition of two different temperature-dependent processes affecting the hydrogen concentration in the core regions of twin boundaries. The amplitude-dependent anelasticity of the R phase is also very sensitive to hydrogen content, its temperature dependence reflects the evolution of extended hydrogen atmospheres near twin boundaries. Full article

(This article belongs to the Special Issue Shape Memory Alloys 2017)

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10 pages, 3186 KiB

Open AccessArticle

Annealing Behavior of 6061 Al Alloy Subjected to Differential Speed Rolling Deformation

by Young Gun Ko¹ and Kotiba Hamad^2,*

¹ School of Materials Science and Engineering, Yeungnam University, Gyeongsan 38541, Korea

² School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 16419, Korea

Metals 2017, 7(11), 494; https://doi.org/10.3390/met7110494 - 10 Nov 2017

Cited by 11 | Viewed by 6338

Abstract

This study investigated the effects of heat treatment (annealing) on the microstructure of ultrafine grained 6061 Al alloy samples fabricated by a differential speed rolling (DSR) process. The samples were fabricated using two passes DSR with 75% thickness reduction and a speed ratio [...] Read more.

This study investigated the effects of heat treatment (annealing) on the microstructure of ultrafine grained 6061 Al alloy samples fabricated by a differential speed rolling (DSR) process. The samples were fabricated using two passes DSR with 75% thickness reduction and a speed ratio of 1:4. The DSR-deformed 6061 Al alloy sample exhibited a lamellar boundary structure composed mostly of subgrains surrounded by low-angle grain boundaries. After annealing, the DSR-deformed 6061 Al alloy samples exhibited coarse grained structure and transformed from lamellar to equiaxed, where both the grain size and grain shape aspect ratio increased with increasing annealing temperature. The fraction of grain boundaries with high misorientation angles increased progressively during annealing, to ~77% at annealing temperature of 350 °C. Full article

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12 pages, 16869 KiB

Open AccessArticle

Effect of Si and Zr on the Microstructure and Properties of Al-Fe-Si-Zr Alloys

by Anna Morozova¹, Anna Mogucheva^1,*, Dmitriy Bukin¹, Olga Lukianova¹, Natalya Korotkova², Nikolay Belov²

and Rustam Kaibyshev¹

¹ Laboratory of Mechanical Properties of Nanostructured Materials and Superalloys, Belgorod State University, Belgorod 308015, Russia

² Department of Casting Technologies, Moscow Institute of steel and Alloys, Moscow 119049, Russia

Metals 2017, 7(11), 495; https://doi.org/10.3390/met7110495 - 11 Nov 2017

Cited by 21 | Viewed by 9473

Abstract

The effects of Si and Zr on the microstructure, microhardness and electrical conductivity of Al-Fe-Si-Zr alloys were studied. An increase in the Zr content over 0.3 wt. % leads to the formation of primary Al₃Zr inclusions and also decreases mechanical properties. [...] Read more.

The effects of Si and Zr on the microstructure, microhardness and electrical conductivity of Al-Fe-Si-Zr alloys were studied. An increase in the Zr content over 0.3 wt. % leads to the formation of primary Al₃Zr inclusions and also decreases mechanical properties. Therefore, the Zr content should not be more than 0.3 wt. %, although the smaller content is insufficient for the strengthening by the secondary Al₃Zr precipitates. The present results indicate that high content of Si significantly affects the hardness and electrical conductivity of the investigated alloys. However, the absence of Si led to the formation of harmful needle-shaped Al₃Fe particles in the microstructure of the investigated alloys after annealing. Therefore, the optimum amount of Si was 0.25–0.50 wt. % due to the formation of the Al₈Fe₂Si phase with the preferable platelet morphology. The maximum microhardness and strengthening effects in Al-1% Fe-0.25% Si-0.3% Zr were observed after annealing at 400–450 °C due to the formation of nanosized coherent Al₃Zr (L1₂) dispersoids. The effect of the increasing of the electrical conductivity can be explained by the decomposition of the solid solution. Thus, Al-1% Fe-0.25% Si-0.3% Zr alloy annealed at 450 °C has been studied in detail as the most attractive with respect to the special focus on transmission line applications. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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14 pages, 5406 KiB

Open AccessArticle

Virtual Testing of Composite Structures Made of High Entropy Alloys and Steel

by Victor Geantă¹, Tudor Cherecheș², Paul Lixandru², Ionelia Voiculescu³, Radu Ștefănoiu^1,*, Daniel Dragnea², Teodora Zecheru⁴ and Liviu Matache⁴

¹ Faculty of Materials Science and Engineering, Politehnica University of Bucharest, 313 Splaiul Independen¸tei, 060042 Bucharest, Romania

² UPS PILOT ARM, 2 Laminorului Street, 137210 Târgovis, te, Romania

³ Faculty of Engineering and Management of Technological Systems, Politehnica University of Bucharest, 313 Splaiul Independen¸tei, 060042 Bucharest, Romania

⁴ Scientific Research Center for CRBN Defense and Ecology Bucharest, Bucharest, 225 Oltenit,ei Road, 041309 Bucharest, Romania

Metals 2017, 7(11), 496; https://doi.org/10.3390/met7110496 - 11 Nov 2017

Cited by 16 | Viewed by 6293

Abstract

High entropy alloys (HEA) are metallic materials obtained from a mixture of at least five atomic-scale chemical elements. They are characterized by high mechanical strength, good thermal stability and hardenability. AlCrFeCoNi alloys have high compression strength and tensile strength values of 2004 MPa, [...] Read more.

High entropy alloys (HEA) are metallic materials obtained from a mixture of at least five atomic-scale chemical elements. They are characterized by high mechanical strength, good thermal stability and hardenability. AlCrFeCoNi alloys have high compression strength and tensile strength values of 2004 MPa, respectively 1250 MPa and elongation of about 32.7%. These materials can be used to create HEA-steel type composite structures which resist to dynamic deformation during high speed impacts. The paper presents four different composite structures made from a combination of HEA and carbon steel plates, using different joining processes. The numerical simulation of the impact behavior of the composite structures was performed by virtual methods, taking into account the mechanical properties of both materials. For analyzing each constructive variant, three virtual shootings were designed, using a 7.62 × 39 mm cal. incendiary armor-piercing bullet and different impact velocities. The best ballistic behavior was provided by the composite structures obtained by welding and brazing that have good continuity and rigidity. The other composite structures, which do not have good surface adhesion, show high fragmentation risk, because the rear plate can fragment on the axis of shooting due to the combination between the shock waves and the reflected ones. The order of materials in the composite structure has a very important role in decreasing the impact energy. Full article

(This article belongs to the Special Issue High-Entropy Alloys (HEAs))

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13 pages, 4396 KiB

Open AccessArticle

The Formation of Composite Ti-Al-N Coatings Using Filtered Vacuum Arc Deposition with Separate Cathodes

by Ivan A. Shulepov¹, Egor B. Kashkarov^1,*

, Igor B. Stepanov¹, Maxim S. Syrtanov¹, Alina N. Sutygina¹, Ivan Shanenkov¹, Aleksei Obrosov²

and Sabine Weiß²

¹ Department of General Physics, National Research Tomsk Polytechnic University, Tomsk 634050, Russia

² Physical Metallurgy and Materials Technology, Brandenburg Technical University, 03046 Cottbus, Germany

Metals 2017, 7(11), 497; https://doi.org/10.3390/met7110497 - 12 Nov 2017

Cited by 14 | Viewed by 5513

Abstract

Ti-Al-N coatings were deposited on high-speed steel substrates by filtered vacuum arc deposition (FVAD) during evaporation of aluminum and titanium cathodes. Distribution of elements, phase composition, and mechanical properties of Ti-Al-N coatings were investigated using Auger electron spectroscopy (AES), X-ray diffraction (XRD), transmission [...] Read more.

Ti-Al-N coatings were deposited on high-speed steel substrates by filtered vacuum arc deposition (FVAD) during evaporation of aluminum and titanium cathodes. Distribution of elements, phase composition, and mechanical properties of Ti-Al-N coatings were investigated using Auger electron spectroscopy (AES), X-ray diffraction (XRD), transmission electron microscopy (TEM) and nanoindentation, respectively. Additionally, tribological tests and scratch tests of the coatings were performed. The stoichiometry of the coating changes from Ti_0.6Al_0.4N to Ti_0.48Al_0.52N with increasing aluminum arc current from 70 A to 90 A, respectively. XRD and TEM showed only face-centered cubic Ti-Al-N phase with preferred orientation of the crystallites in (220) direction with respect to the sample normal and without precipitates of AlN or intermetallics inside the coatings. Incorporation of Al into the TiN lattice caused shifting of the (220) reflex to a higher 2θ angle with increasing Al content. Low content and size of microdroplets were obtained using coaxial plasma filters, which provides good mechanical and tribological properties of the coatings. The highest value of microhardness (36 GPa) and the best wear-resistance were achieved for the coating with higher Al content, thus for Ti_0.48Al_0.52N. These coatings exhibit good adhesive properties up to 30 N load in the scratch tests. Full article

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12 pages, 5166 KiB

Open AccessArticle

Investigation of the Deformation Mechanism of a near β Titanium Alloy through Isothermal Compression

by Jie Wu¹, Zhidan Lü¹, Changjiang Zhang^1,*, Jianchao Han², Hongzhou Zhang³, Shuzhi Zhang¹, Muhammad Hayat³ and Peng Cao^3,*

¹ School of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China

² School of Mechanical Engineering, Taiyuan University of Technology, Taiyuan 030024, China

³ Department of Chemical and Materials Engineering, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand

Metals 2017, 7(11), 498; https://doi.org/10.3390/met7110498 - 12 Nov 2017

Cited by 13 | Viewed by 4810

Abstract

This study investigated the hot deformation behavior of Ti-4Al-1Sn-2Zr-5Mo-8V-2.5Cr alloy through isothermal compression tests at temperatures from 780 to 930 °C with strain rates ranging from 0.001 to 1 s⁻¹. The flow stress decreases with a decreased strain rate and an [...] Read more.

This study investigated the hot deformation behavior of Ti-4Al-1Sn-2Zr-5Mo-8V-2.5Cr alloy through isothermal compression tests at temperatures from 780 to 930 °C with strain rates ranging from 0.001 to 1 s⁻¹. The flow stress decreases with a decreased strain rate and an increased temperature. A constitutive equation was established for this alloy and the dependence of activation energy on temperature and strain rate is discussed. We further proposed a processing map using the dynamic materials model. On the processing map various domains of flow stability and flow instability can be identified. The deformation mechanisms associated with flow stability regions are mainly dynamic recrystallization (DRX) and dynamic recovery (DRV). The flow instability is manifested in the form of the band of flow localizations. The optimum processing conditions are suggested such that the temperature range is from 780 to 880 °C and the strain rate ranges from 0.001 to 0.01 s⁻¹. Full article

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14 pages, 15211 KiB

Open AccessArticle

Reduced Graphene Oxide Reinforced 7075 Al Matrix Composites: Powder Synthesis and Mechanical Properties

by Youhong Sun^1,2, Chi Zhang^1,2, Baochang Liu^1,2,*, Qingnan Meng^1,2,*, Shaoming Ma^1,2 and Wenhao Dai¹

¹ School of Construction Engineering, Jilin University, Changchun 130026, China

² Key Laboratory of Drilling and Exploitation Technology in Complex Conditions, Ministry of Land and Resources, No. 938 Ximinzhu Street, Changchun 130026, China

Metals 2017, 7(11), 499; https://doi.org/10.3390/met7110499 - 13 Nov 2017

Cited by 30 | Viewed by 7909

Abstract

Reduced graphene oxide (rGO) reinforced 7075 Al matrix composites were fabricated by electrostatic self-assembly and powder metallurgy. 7075 Al powders were surface modified by introducing a cetyl trimethyl ammonium bromide (CTAB) membrane on the surface, which was able to form a strong bonding [...] Read more.

Reduced graphene oxide (rGO) reinforced 7075 Al matrix composites were fabricated by electrostatic self-assembly and powder metallurgy. 7075 Al powders were surface modified by introducing a cetyl trimethyl ammonium bromide (CTAB) membrane on the surface, which was able to form a strong bonding with graphene oxide (GO) through electrostatic interaction. During the vacuum sintering process, CTAB was effectively removed and GO was thermally reduced into rGO. Morphologies of GO nanosheets, GO/7075 Al powders, microstructures, and tensile fractographs of the composites were observed. The effect of rGO content on mechanical properties of rGO/7075 Al composites was investigated. The results show that a good bonding between rGO and matrix is achieved. With the rGO content increasing, the hardness increases gradually, while the ultimate tensile strength and yield strength initially increase and later decrease. The improvement in strength of rGO/7075 Al composites was attributed to stress transfer and dislocation strengthening. With rGO content reaching 0.50 wt %, the excessive addition of rGO gave rise to a weakening in the enhancement of the tensile properties due to the increasing amounts of brittle Al₄C₃ and cracks. Full article

(This article belongs to the Special Issue Metal Matrix Composites)

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9 pages, 13209 KiB

Open AccessArticle

Microstructure and Properties of Porous Si₃N₄/Dense Si₃N₄ Joints Bonded Using RE–Si–Al–O–N (RE = Y or Yb) Glasses

by Ling Li, Liangbo Sun

, Chunfeng Liu^*, Xinhua Wang, Xuanzhi Wang and Jie Zhang^*

School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China

Metals 2017, 7(11), 500; https://doi.org/10.3390/met7110500 - 13 Nov 2017

Cited by 9 | Viewed by 4589

Abstract

The joining of porous Si₃N₄ to dense Si₃N₄ ceramics has been successfully performed using mixed RE₂O₃ (RE = Y or Yb), Al₂O₃, SiO₂, and α-Si₃N₄ [...] Read more.

The joining of porous Si₃N₄ to dense Si₃N₄ ceramics has been successfully performed using mixed RE₂O₃ (RE = Y or Yb), Al₂O₃, SiO₂, and α-Si₃N₄ powders. The results suggested that the α-Si₃N₄ powders partly transformed into β-SiAlON and partly dissolved into oxide glass to form oxynitride glass. Thus, composites of glass/β-SiAlON-ceramic formed in the seam of joints. Due to the capillary action of the porous Si₃N₄ ceramic, the molten glass solder infiltrated into the porous Si₃N₄ ceramic side during the joining process and formed the “infiltration zone” with a thickness of about 400 μm, which contributed to the heterogeneous distribution of the RE–Si–Al–O–N glasses in the porous Si₃N₄ substrate. In-situ formation of β-SiAlON in the seam resulted in a high bonding strength. The maximum bending strength of 103 MPa and 88 MPa was reached for the porous Si₃N₄/dense Si₃N₄ joints using Y–Si–Al–O–N and Yb–Si–Al–O–N glass solders, respectively. Full article

(This article belongs to the Special Issue Diffusion Bonding and Brazing of Advanced Materials)

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14 pages, 4904 KiB

Open AccessArticle

Fabrication and Characterization of a Low Magnetic Zr-1Mo Alloy by Powder Bed Fusion Using a Fiber Laser

by Xiaohao Sun¹, Weiwei Zhou¹, Keiko Kikuchi¹, Naoyuki Nomura^1,*, Akira Kawasaki¹, Hisashi Doi², Yusuke Tsutsumi² and Takao Hanawa²

¹ Department of Materials Processing, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan

² Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Tokyo 101-0062, Japan

Metals 2017, 7(11), 501; https://doi.org/10.3390/met7110501 - 13 Nov 2017

Cited by 22 | Viewed by 6475

Abstract

A low magnetic Zr-1Mo alloy was fabricated by a powder bed fusion (PBF) process using a fiber laser. The microstructure, surface morphology, and pore distribution of the as-built Zr-1Mo alloy were observed. Its magnetic susceptibility and Vickers hardness were evaluated by magnetic susceptibility [...] Read more.

A low magnetic Zr-1Mo alloy was fabricated by a powder bed fusion (PBF) process using a fiber laser. The microstructure, surface morphology, and pore distribution of the as-built Zr-1Mo alloy were observed. Its magnetic susceptibility and Vickers hardness were evaluated by magnetic susceptibility balance and a microindentation tester, respectively. The as-built Zr-1Mo alloy mainly consisted of an α′ phase with an acicular structure. From the processing maps of the surface morphology and pore distribution, open pores on the top surface due to the lack of fusion corresponded to grid-like distributed pores, and large pores corresponded to balling particles on the top surface. The Vickers hardness was influenced by the oxygen and nitrogen contents rather than the porosity. The magnetic susceptibilities of the as-built Zr-1Mo alloy still were one-third those of Ti-6Al-4V and Ti-6Al-7Nb, thus PBF can be applicable to the fabrication process for the low magnetic Zr-1Mo alloy. Full article

(This article belongs to the Special Issue Zirconium Alloys)

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11 pages, 2457 KiB

Open AccessArticle

Effects of Matte Grade on the Distribution of Minor Elements (Pb, Zn, As, Sb, and Bi) in the Bottom Blown Copper Smelting Process

by Qinmeng Wang¹

, Xueyi Guo^2,*, Qinghua Tian^2,*, Tao Jiang¹, Mao Chen³ and Baojun Zhao³

¹ School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China

² School of Metallurgy and Environment, Central South University, Changsha 410083, China

³ School of Chemical Engineering, University of Queensland, Brisbane, QLD 4702, Australia

Metals 2017, 7(11), 502; https://doi.org/10.3390/met7110502 - 14 Nov 2017

Cited by 27 | Viewed by 6932

Abstract

With increasing impurity contents in concentrates, the control of the minor elements is an important issue for the oxygen bottom blown copper smelting process (Shuikoushan process or SKS process). In this work, the distribution behaviors of the minor elements (such as Pb, Zn, [...] Read more.

With increasing impurity contents in concentrates, the control of the minor elements is an important issue for the oxygen bottom blown copper smelting process (Shuikoushan process or SKS process). In this work, the distribution behaviors of the minor elements (such as Pb, Zn, As, Sb, and Bi) among the matte, slag, and gas phases as a function of matte grades was investigated by adjusting the ratios of oxygen/ore in the SKS process. With a matte grade around 70%, about 82% As and 70% Bi enters the gas phase, and about 70% Sb and 64% Zn reports to the slag phase, while 55% lead enters the matte phase. The tendency of changes in the distribution of the minor elements in the SKS process is different from that in the Isasmelt process and the Flash smelting process. It may be concluded from this study that the distributions of the minor elements could be optimized to reduce adverse effects in the SKS process by regulating the matte grade. Full article

(This article belongs to the Special Issue Heavy Metal Determination and Removal)

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9 pages, 2631 KiB

Open AccessArticle

Effect of Nitrogen on Deformation-Induced Martensitic Transformation in an Austenitic 301 Stainless Steels

by Jong Bae Jeon^1,* and Young Won Chang^2,*

¹ Functional Components and Materials R&D Group, Korea Institute of Industrial Technology, Yangsan 50635, Korea

² Department of Materials Science and Engineering, POSTECH, Pohang 37673, Korea

Metals 2017, 7(11), 503; https://doi.org/10.3390/met7110503 - 13 Nov 2017

Cited by 13 | Viewed by 5692

Abstract

The effect of nitrogen on deformation-induced martensitic transformation (DIMT) in metastable 301 austenitic stainless steel has been studied based on the inelastic deformation theory. DIMT is regarded here as continuous relaxation process of internal strain energy accumulated during inelastic deformation. Using the kinetics [...] Read more.

The effect of nitrogen on deformation-induced martensitic transformation (DIMT) in metastable 301 austenitic stainless steel has been studied based on the inelastic deformation theory. DIMT is regarded here as continuous relaxation process of internal strain energy accumulated during inelastic deformation. Using the kinetics equation based on the inelastic deformation theory the relationship between the volume fraction of transformed martensite and inelastic strain for DIMT has been successfully verified with the parameter representing the stability of austenite. The addition of nitrogen is experimentally found to increase austenite stability and the critical inelastic strain below which any DIMT is not observed to occur and to decrease the saturation volume fraction of α’ martensite. On the other hand, DIMT has been analyzed with its effect on stress-strain curve shape and mechanical properties in relation to the addition of nitrogen. The characteristic transition from sigmoidal to parabolic curve shape in stress-strain response has disappeared with the addition of nitrogen. Full article

(This article belongs to the Special Issue Deformation-Induced Phase Transformations in Steels and Non-Ferrous Alloys)

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12 pages, 10746 KiB

Open AccessFeature PaperArticle

Laser Welding of BTi-6431S High Temperature Titanium Alloy

by Zhi Zeng^1,*, J. P. Oliveira², Xianzheng Bu³, Mao Yang¹, Ruoxi Li⁴ and Zhimin Wang^3,*

¹ School of Mechatronics Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China

² Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43221, USA

³ Beijing Hangxing Machinery Manufacture Limited Corporation, Beijing 100013, China

⁴ College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China

Metals 2017, 7(11), 504; https://doi.org/10.3390/met7110504 - 15 Nov 2017

Cited by 8 | Viewed by 5586

Abstract

A new type of high temperature titanium alloy, BTi-6431S, has recently become the focus of attention as a potential material for aircraft engine applications, which could be used up to 700 °C. Pulsed laser welding was used to butt join the BTi-6431S titanium [...] Read more.

A new type of high temperature titanium alloy, BTi-6431S, has recently become the focus of attention as a potential material for aircraft engine applications, which could be used up to 700 °C. Pulsed laser welding was used to butt join the BTi-6431S titanium alloy in order to understand the feasibility of using fusion-based welding techniques on this material. The effect of laser energy on the microstructure and mechanical properties of the joints was investigated. The microstructural features of the joints were characterized by means of microscopy and X-ray diffraction. Tensile testing was conducted at both room temperature and high temperature to simulate potential service conditions. The results show that the microstructure of the laser welded joints consists of primary α phase and needle α’ phase, while the microstructure of the heat affected zone consists of α, β, and needle α’ phases. The tensile strength of the welded joints at room temperature was similar to that of the base material, despite a reduction in the maximum elongation was observed. This was related to the unfavorable microstructure in the welded joints. Nonetheless, based on these results, it is suggested that laser welding is a promising joining technique for the new BTi-6431S titanium alloy for aerospace applications. Full article

(This article belongs to the Special Issue Laser Welding)

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16 pages, 1383 KiB

Open AccessFeature PaperReview

Recycling of Palladium from Spent Catalysts Using Solvent Extraction—Some Critical Points

by Ana Paula Paiva

Centro de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Campo Grande C8, 1749-016 Lisbon, Portugal

Metals 2017, 7(11), 505; https://doi.org/10.3390/met7110505 - 16 Nov 2017

Cited by 45 | Viewed by 10211

Abstract

Electrical and electronics equipment and automotive and industrial catalysts are some examples of top technological devices whose functioning rely on the use of platinum-group metals (PGMs). The PGMs’ high economic value and difficult to replace technological properties, together with their scarcity in the [...] Read more.

Electrical and electronics equipment and automotive and industrial catalysts are some examples of top technological devices whose functioning rely on the use of platinum-group metals (PGMs). The PGMs’ high economic value and difficult to replace technological properties, together with their scarcity in the Earth’s crust, justify concerns about their critical condition and reinforce the importance of developing recycling practices for PGM end-of-life materials. This article presents and discusses recent advances regarding the use of hydrometallurgical solvent extraction to recover one PGM, palladium, from spent catalysts. Two different tendencies are implicit in the literature concerning Pd(II) extraction: a few groups focus on the adjustment and optimization of current commercial extractants, while others prefer to design new extracting compounds. Actually, the leach solutions obtained from the treatment of anthropogenic materials generally exhibit different compositions when compared to those coming from the primary resources. The pros and cons of both approaches are critically discussed, and the assumptions backing some of the reported achievements are also appraised. Full article

(This article belongs to the Special Issue Solvent Extraction of Critical Metals)

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21 pages, 61834 KiB

Open AccessArticle

Thermo-Calc Prediction of Mushy Zone in AlSiFeMn Alloys

by Piotr Mikolajczak^1,*

, Amber Genau², Jerzy Janiszewski³ and Lorenz Ratke⁴

¹ Institute of Materials Technology, Poznan University of Technology, Piotrowo 3, 60-965 Poznan, Poland

² Department of Materials Science and Engineering, University of Alabama at Birmingham, 1720 2nd Avenue South, Birmingham, AL 35294, USA

³ Institute of Electrical Power Engineering, Poznan University of Technology, Piotrow 3A, 60-965 Poznan, Poland

⁴ Institut fürWerkstoff-Forschung, German Aerospace Center DLR, Linder Höhe, 51147 Köln, Germany

Metals 2017, 7(11), 506; https://doi.org/10.3390/met7110506 - 16 Nov 2017

Cited by 7 | Viewed by 7183

Abstract

Convection forces can cause significant segregation within the liquid during directional solidification, influencing the structure of the mushy zone and the type and distribution of phases present in the solidified alloy. The solidification behavior of AlSiFeMn alloys with strong convection was investigated via [...] Read more.

Convection forces can cause significant segregation within the liquid during directional solidification, influencing the structure of the mushy zone and the type and distribution of phases present in the solidified alloy. The solidification behavior of AlSiFeMn alloys with strong convection was investigated via experimental results combined with thermodynamic calculations. Experimental specimens were processed in a directional solidification facility with forced melt flow, resulting in high levels of elemental segregation across samples. The resulting local compositions were located on phase diagrams Al-Si-Fe, Al-Si-Mn and Al-Fe-Mn for prediction of the variation in solidification behavior. Phase mass fraction diagrams created in Thermo-Calc showed the effect of segregation on the characteristic temperatures, mushy zone length and the order of occurring phases precipitating across specimens. These findings were used to create 2D maps for visualization of the mushy zone, mass fraction of α-Al dendrites, β-Al₅FeSi, Al₁₅Si₂Mn₄ and their spatial location. The specimen centers showed enrichment in AlSi-eutectic but for β-Al₅FeSi and Al₁₅Si₂Mn₄ results are ambiguous. Fe-phases start to grow mainly behind the dendrites tips and in general may flow between them. Mn-rich phases start to precipitate at higher temperatures than β and in many places before α-Al and in this way may flow in the melt above the mushy zone. Full article

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12 pages, 4612 KiB

Open AccessArticle

Effect of High-Pressure Torsion on Structure and Microhardness of Ti/TiB Metal–Matrix Composite

by Sergey Zherebtsov¹, Maxim Ozerov^1,*, Nikita Stepanov¹

, Margarita Klimova¹ and Yulia Ivanisenko²

¹ Laboratory of Bulk Nanostructured Materials, Belgorod State University, Belgorod 308015, Russia

² Karlsruhe Institute of Technology, Institute of Nanotechnology, 76021 Karlsruhe, Germany

Metals 2017, 7(11), 507; https://doi.org/10.3390/met7110507 - 16 Nov 2017

Cited by 14 | Viewed by 4908

Abstract

Effect of high-pressure torsion (HPT) at 400 °C on microstructure and microhardness of a Ti/TiB metal–matrix composite was studied. The starting material was produced by spark plasma sintering of a mixture of a pure Ti and TiB₂ (10 wt %) powders at [...] Read more.

Effect of high-pressure torsion (HPT) at 400 °C on microstructure and microhardness of a Ti/TiB metal–matrix composite was studied. The starting material was produced by spark plasma sintering of a mixture of a pure Ti and TiB₂ (10 wt %) powders at 1000 °C. The microstructure evolution during HPT was associated with an increase in dislocation density and substructure development that resulted in a gradual microstructure refinement of the Ti matrix and shortening/redistribution of TiB whiskers. After five revolutions, a nanostructure with (sub) grain size of ~30 nm was produced in Ti matrix. The microhardness increased with strain attaining the value ~520 HV after five revolutions. The contribution of different hardening mechanisms into the hardness of the Ti/TiB metal–matrix composite was quantitatively analyzed. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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12 pages, 1826 KiB

Open AccessArticle

Assessment of the Contour Method for 2-D Cross Sectional Residual Stress Measurements of Friction Stir Welded Parts of AA2024-T3—Numerical and Experimental Comparison

by Mads R. Sonne^1,*, Pierpaolo Carlone²

and Jesper H. Hattel¹

¹ Department of Mechanical Engineering, Technical University of Denmark, 2800 Lyngby, Denmark

² Department of Industrial Engineering, University of Salerno, 84084 Fisciano, Italy

Metals 2017, 7(11), 508; https://doi.org/10.3390/met7110508 - 19 Nov 2017

Cited by 5 | Viewed by 4703

Abstract

The contour method is one of the newest techniques for obtaining residual stress fields from friction stir welded (FSW) parts, experimentally. This method has many advantages; however, edge effects coming from the process itself might introduce artifacts in the obtained results, and this [...] Read more.

The contour method is one of the newest techniques for obtaining residual stress fields from friction stir welded (FSW) parts, experimentally. This method has many advantages; however, edge effects coming from the process itself might introduce artifacts in the obtained results, and this was slightly touched upon in the very first paper on the method. This concern is further assessed in the present work, where the contour method is compared with the results that were obtained numerically via a thermomechanical model and experimentally via the cut-compliance method. For the two-dimensional (2-D) cross sectional map obtained by the method, peak stresses in tension are observed in the mid-section of the FSW butt-welded plates at the distance of the tool radius from the centerline. The corresponding numerical simulation indicates the same behavior because of the particular clamping conditions, and consequently this should not be interpreted as a misleading result of the contour method. Edge effects from the cutting process involved in the contour method should, however, be taken into consideration, most likely resulting in the residual stresses observed near the surfaces of the cross section being less extreme in reality than observed. Full article

(This article belongs to the Special Issue Experimental Assessment of Residual Stress in Engineering Materials Components)

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11 pages, 1136 KiB

Open AccessArticle

Entropy Change Caused by Martensitic Transformations of Ferromagnetic Shape Memory Alloys

by Victor A. L’vov^1,2

, Eduard Cesari³

, Anna Kosogor^2,*, Joan Torrens-Serra³, Vicente Recarte⁴

and José Ignacio Pérez-Landazábal⁴

¹ Faculty of Radiophysics, Electronics and Computer Systems, Taras Shevchenko University, Glushkov Str. 4G, Kyiv 01601, Ukraine

² Department of Theory of Magnetic Phenomena and Magnetic Dynamics of Solid State, Institute of Magnetism, 36-b, Vernadsky Str., Kyiv 03142, Ukraine

³ Departament de Fisica, Universitat de les Illes Balears, Ctra. de Valldemossa, km 7.5, Palma de Mallorca 07122, Spain

⁴ Departamento de Física, Universidad Pública de Navarra (UPNA), Campus Arrosadia, Pamplona 31006, Spain

Metals 2017, 7(11), 509; https://doi.org/10.3390/met7110509 - 19 Nov 2017

Cited by 1 | Viewed by 4028

Abstract

In this paper, our most recent findings on the influence of magnetic order on the main transformational caloric and elastic properties of shape memory alloys (SMAs) are reviewed. It is argued that ferromagnetic order has a strong influence on the temperature interval of [...] Read more.

In this paper, our most recent findings on the influence of magnetic order on the main transformational caloric and elastic properties of shape memory alloys (SMAs) are reviewed. It is argued that ferromagnetic order has a strong influence on the temperature interval of martensitic transformation (MT), the characteristics of stress-induced MT, and the shear elastic modulus of SMA. The problem of separation of the magnetic contributions to the entropy change ΔS and heat Q exchanged in the course of martensitic transformation (MT) of SMA is considered in general terms, and theoretical formulas enabling the solution of the problem are presented. As an example, the ΔS and Q values, which were experimentally determined for Ni-Mn-Ga and Ni-Fe-Ga alloys with different Curie temperatures T_C and MT temperatures T_M, are theoretically analyzed. It is shown that for Ni-Mn-Ga martensites with T_M < T_C, the ratio of elastic and magnetic contributions to the entropy change may be greater or smaller than unity, depending on the temperature difference T_C – T_M. Full article

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15 pages, 17693 KiB

Open AccessFeature PaperArticle

Effect of the Ultrasonic Nanocrystalline Surface Modification (UNSM) on Bulk and 3D-Printed AISI H13 Tool Steels

by In-Sik Cho¹, Chang-Soon Lee¹, Chang-Ha Choi¹, Hyung-Gyu Lee², Moon Gu Lee² and Yongho Jeon^2,*

¹ Department of Advanced Material Engineering, Sun Moon University, 70, Sunmoon-ro 221 beon-gil, Tangjeong-myeon, Asan-si, Chungcheongnam-do 31460, Korea

² Department of Mechanical Engineering, Ajou University, 206 Worldcup-ro, Yeongtong-gu, Suwon 16499, Korea

Metals 2017, 7(11), 510; https://doi.org/10.3390/met7110510 - 21 Nov 2017

Cited by 18 | Viewed by 6156

Abstract

A comparative study of the microstructure, hardness, and tribological properties of two different AISI H13 tool steels—classified as the bulk with no heat treatment steel or the 3D-printed steel—was undertaken. Both samples were subjected to ultrasonic nanocrystalline surface modification (UNSM) to further enhance [...] Read more.

A comparative study of the microstructure, hardness, and tribological properties of two different AISI H13 tool steels—classified as the bulk with no heat treatment steel or the 3D-printed steel—was undertaken. Both samples were subjected to ultrasonic nanocrystalline surface modification (UNSM) to further enhance their mechanical properties and improve their tribological behavior. The objective of this study was to compare the mechanical properties and tribological behavior of these tool steels since steel can exhibit a wide variety of mechanical properties depending on different manufacturing processes. The surface hardness of the samples was measured using a micro-Vickers hardness tester. The hardness of the 3D-printed AISI H13 tool steel was found to be much higher than that of the bulk one. The surface morphology of the samples was characterized by electron backscattered diffraction (EBSD) in order to analyze the grain size and number of fractions with respect to the misorientation angle. The results revealed that the grain size of the 3D-printed AISI H13 tool steel was less than 0.5 μm, whereas that of the bulk tool steel was greater than 4 μm. The number of fractions of the bulk tool steel was about 0.5 μm at a low misorientation angle, and it decreased gradually with increasing misorientation angle. The low-angle grain boundary (LAGB) and high-angle grain boundary (HAGB) of the bulk sample were about 21% and 79%, respectively, and those of the 3D-printed sample were about 8% and 92%, respectively. Moreover, the friction and wear behavior of the UNSM-treated AISI H13 tool steel specimen was better than those of the untreated one. This study demonstrated the capability of 3D-printed AISI H13 tool steel to exhibit excellent mechanical and tribological properties for industrial applications. Full article

(This article belongs to the Special Issue Synthesis and Properties of Bulk Nanostructured Metallic Materials)

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15 pages, 4997 KiB

Open AccessArticle

Effect of Ni-Content on the Transformation Temperatures in NiTi-20 at. % Zr High Temperature Shape Memory Alloys

by Matthew Carl^1,*, Jesse D. Smith¹, Brian Van Doren² and Marcus L. Young¹

¹ Department of Materials Science and Engineering, University of North Texas, Denton, TX 76203, USA

² ATI Specialty Alloys and Components, Albany, OR 97321, USA

Metals 2017, 7(11), 511; https://doi.org/10.3390/met7110511 - 21 Nov 2017

Cited by 30 | Viewed by 8465

Abstract

The effect of Ni-content on phase transformation behavior of NiTi-20 at. % Zr high temperature shape memory alloy (HTSMA) is investigated over a small composition range, i.e., 49.8, 50.0 and 50.2 at. % Ni, by differential scanning calorimetry (DSC), high-energy synchrotron radiation X-ray [...] Read more.

The effect of Ni-content on phase transformation behavior of NiTi-20 at. % Zr high temperature shape memory alloy (HTSMA) is investigated over a small composition range, i.e., 49.8, 50.0 and 50.2 at. % Ni, by differential scanning calorimetry (DSC), high-energy synchrotron radiation X-ray diffraction (SR-XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). All samples show a monoclinic B19^′ martensitic structure at room temperature. It is shown that even with these small variations in Ni-content, the alloy shows vastly different transformation temperatures and responds in a drastically different manner to aging treatments at 550 and 600 °C. Lastly, a discussion on H-phase composition with respect to bulk composition is presented. Full article

(This article belongs to the Special Issue Shape Memory Alloys 2017)

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10 pages, 6512 KiB

Open AccessArticle

Microstructure and Microhardness of Laser Metal Deposition Shaping K465/Stellite-6 Laminated Material

by Zhiguo Wang^1,*

, Jibin Zhao¹, Yuhui Zhao¹, Hongyu Zhang² and Fan Shi¹

¹ Equipment Manufacturing Technology Research Laboratory, Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang 110016, China

² Superalloys Division, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China

Metals 2017, 7(11), 512; https://doi.org/10.3390/met7110512 - 22 Nov 2017

Cited by 9 | Viewed by 5359

Abstract

K465 superalloy with high titanium and aluminum contents was easy to crack during laser metal deposition. In this study, the crack-free sample of K465/Stellite-6 laminated material was formed by laser metal deposition shaping to control the cracking behaviour in laser metal deposition of [...] Read more.

K465 superalloy with high titanium and aluminum contents was easy to crack during laser metal deposition. In this study, the crack-free sample of K465/Stellite-6 laminated material was formed by laser metal deposition shaping to control the cracking behaviour in laser metal deposition of K465 superalloy. The microstructure differences between the K465 superalloy with cracking and the laminated material were discussed. The microstructure and intermetallic phases were analyzed through scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results showed that the microstructure of K465/Stellite-6 laminated material samples consisted of continuous dendrites with a similar structure size in different alloy deposition layers, and the second dendrite arm spacing was finer compared with laser metal deposition shaping K465. The intermetallic phases in the different alloy deposition layers varied, and the volume fraction of carbides in K465 deposition layer of the laminated material was higher than only K465 deposition under the fluid flow effect. In addition, the composition and microhardness distribution of laminated materials variation occurred along the deposition direction. Full article

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13 pages, 9998 KiB

Open AccessArticle

Optimization of Thermo-Mechanical Processing for Forging of Newly Developed Creep-Resistant Magnesium Alloy ABaX633

by Kamineni Pitcheswara Rao^1,*

, Chalasani Dharmendra¹

, Yellapregada Venkata Rama Krishna Prasad², Norbert Hort³ and Hajo Dieringa³

¹ Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong

² Independent Researcher, No. 2/B, Vinayaka Nagar, Bengaluru 560024, India

³ Magnesium Innovation Centre, Helmholtz Zentrum Geesthacht, Max-Planck-Strasse 1, 21502 Geesthacht, Germany

Metals 2017, 7(11), 513; https://doi.org/10.3390/met7110513 - 21 Nov 2017

Cited by 4 | Viewed by 5291

Abstract

The compressive strength and creep resistance of cast Mg-6Al-3Ba-3Ca (ABaX633) alloy has been measured in the temperature range of 25 to 250 °C, and compared with that of its predecessor ABaX422. The alloy is stronger and more creep-resistant than ABaX422, and exhibits only [...] Read more.

The compressive strength and creep resistance of cast Mg-6Al-3Ba-3Ca (ABaX633) alloy has been measured in the temperature range of 25 to 250 °C, and compared with that of its predecessor ABaX422. The alloy is stronger and more creep-resistant than ABaX422, and exhibits only a small decrease of yield stress with temperature. The higher strength of ABaX633 is attributed to a larger volume fraction of intermetallic particles (Al, Mg)₂Ca and Mg₂₁Al₃Ba₂ in its microstructure. Hot deformation mechanisms in ABaX633 have been characterized by developing a processing map in the temperature and strain rate ranges of 300 to 500 °C and 0.0003 to 10 s⁻¹. The processing map exhibits two workability domains in the temperature and strain rate ranges of: (1) 380 to 475 °C and 0.0003 to 0.003 s⁻¹, and (2) 480–500 °C and 0.003 to 0.5 s⁻¹. The apparent activation energy values estimated in the above two domains (204 and 216 kJ/mol) are higher than that for lattice self-diffusion of Mg, which is attributed to the large back-stress that is caused by the intermetallic particles. Optimum condition for bulk working is 500 °C and 0.01 s⁻¹ at which hot workability will be maximum. Flow instability is exhibited at lower temperatures and higher strain rates, as well as at higher temperatures and higher strain rates. The predictions of the processing map on the workability domains, as well as the instability regimes are fully validated by the forging of a rib-web (cup) shaped component under optimized conditions. Full article

(This article belongs to the Special Issue Light Weight Alloys: Processing, Properties and Their Applications)

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14 pages, 898 KiB

Open AccessFeature PaperReview

The Biological Responses to Magnesium-Based Biodegradable Medical Devices

by Lumei Liu^1,2

, Juan Wang³, Teal Russell^1,2, Jagannathan Sankar¹ and Yeoheung Yun^1,2,*

¹ National Science Foundation-Engineering Research Center for Revolutionizing Metallic Biomaterials, North Carolina Agricultural and Technical State University, Greensboro, NC 27401, USA

² FIT BEST Laboratory, Department of Chemical, Biological, and Bioengineering, North Carolina Agricultural and Technical State University, Greensboro, NC 27401, USA

³ Department of Anesthesiology, School of Medicine, Yale University, New Haven, CT 06519, USA

Metals 2017, 7(11), 514; https://doi.org/10.3390/met7110514 - 21 Nov 2017

Cited by 23 | Viewed by 7110

Abstract

The biocompatibility of Magnesium-based materials (MBMs) is critical to the safety of biodegradable medical devices. As a promising metallic biomaterial for medical devices, the issue of greatest concern is devices’ safety as degrading products are possibly interacting with local tissue during complete degradation. [...] Read more.

The biocompatibility of Magnesium-based materials (MBMs) is critical to the safety of biodegradable medical devices. As a promising metallic biomaterial for medical devices, the issue of greatest concern is devices’ safety as degrading products are possibly interacting with local tissue during complete degradation. The aim of this review is to summarize the biological responses to MBMs at the cellular/molecular level, including cell adhesion, transportation signaling, immune response, and tissue growth during the complex degradation process. We review the influence of MBMs on gene/protein biosynthesis and expression at the site of implantation, as well as throughout the body. This paper provides a systematic review of the cellular/molecular behavior of local tissue on the response to Mg degradation, which may facilitate a better prediction of long-term degradation and the safe use of magnesium-based implants through metal innovation. Full article

(This article belongs to the Special Issue Biodegradable Metals)

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