Metals

7 pages, 759 KiB

Open AccessFeature PaperTechnical Note

Tensile Ductility of Nanostructured Bainitic Steels: Influence of Retained Austenite Stability

by Thomas Sourmail, Carlos Garcia-Mateo, Francisca G. Caballero, Lucia Morales-Rivas, Rosalia Rementeria and Matthias Kuntz

Metals 2017, 7(1), 31; https://doi.org/10.3390/met7010031 - 23 Jan 2017

Cited by 31 | Viewed by 6134

Abstract

High silicon (>1.5%) steels with different compositions were isothermally transformed to bainite at 220 and 250 °C to produce what is often referred to as nanostructured bainite. Interrupted tensile tests were carried out and the retained austenite was measured as a function of [...] Read more.

High silicon (>1.5%) steels with different compositions were isothermally transformed to bainite at 220 and 250 °C to produce what is often referred to as nanostructured bainite. Interrupted tensile tests were carried out and the retained austenite was measured as a function of strain. Results were correlated with tensile ductility. The role of retained austenite stability is remarkably underlined as strongly affecting the propensity to brittle failure, but also the tensile ductility. A simple quantitative relationship is proposed that clearly delimitates the different behaviours (brittle/ductile) and correlates well with the measured ductility. Conclusions are proposed as to the role of retained austenite fraction and the existence of a threshold value associated with tensile rupture. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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12 pages, 3503 KiB

Open AccessArticle

Electropolishing Behaviour of 73 Brass in a 70 vol % H₃PO₄ Solution by Using a Rotating Cylinder Electrode (RCE)

by Ching An Huang, Jhih You Chen and Ming Tsung Sun

Metals 2017, 7(1), 30; https://doi.org/10.3390/met7010030 - 20 Jan 2017

Cited by 5 | Viewed by 4488

Abstract

The electropolishing behaviour of 73 brass was studied by means of a rotating cylinder electrode (RCE) in a 70 vol % H₃PO₄ solution at 27 °C. Owing to the formation of a blue Cu²⁺-rich layer on the brass-RCE, [...] Read more.

The electropolishing behaviour of 73 brass was studied by means of a rotating cylinder electrode (RCE) in a 70 vol % H₃PO₄ solution at 27 °C. Owing to the formation of a blue Cu²⁺-rich layer on the brass-RCE, an obvious transition peak was detected from kinetic- to diffusion-controlled dissolution in the anodic polarisation curve. Electropolishing was conducted at the potentials located at the transition peak, the start, the middle, and the end positions in the limiting-current plateau corresponding to the anodic polarisation curve of the brass-RCE. A well-polished surface can be obtained after potentiostatic electropolishing at the middle position in the limiting-current plateau. During potentiostatic etching in the limiting-current plateau, a blue Cu²⁺-rich layer was formed on the brass-RCE, reducing its anodic dissolution rate and obtaining a levelled and brightened brass-RCE. Moreover, a rod climbing phenomenon of the blue Cu²⁺-rich layer was observed on the rotating brass-RCE. This enhances the coverage of the Cu²⁺-rich layer on the brass-RCE and improves its electropolishing effect obviously. Full article

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13 pages, 4826 KiB

Open AccessArticle

Effect of Annealing Temperature on the Corrosion Protection of Hot Swaged Ti-54M Alloy in 2 M HCl Pickling Solutions

by El-Sayed M. Sherif, Ehab A. El Danaf, Hany S. Abdo, Sherif Zein El Abedin and Hasan Al-Khazraji

Metals 2017, 7(1), 29; https://doi.org/10.3390/met7010029 - 20 Jan 2017

Cited by 7 | Viewed by 4715

Abstract

The corrosion of Ti-54M titanium alloy processed by hot rotary swaging and post-annealed to yield different grain sizes, in 2 M HCl solutions is reported. Two annealing temperatures of 800 °C and 940 °C, followed by air cooling and furnace cooling were used [...] Read more.

The corrosion of Ti-54M titanium alloy processed by hot rotary swaging and post-annealed to yield different grain sizes, in 2 M HCl solutions is reported. Two annealing temperatures of 800 °C and 940 °C, followed by air cooling and furnace cooling were used to give homogeneous grain structures of 1.5 and 5 μm, respectively. It has been found that annealing the alloy at 800 °C decreased the corrosion of the alloy, with respect to the hot swaged condition, through increasing its corrosion resistance and decreasing the corrosion current and corrosion rate. Increasing the annealing temperature to 940 °C further decreased the corrosion of the alloy. Full article

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20 pages, 7545 KiB

Open AccessArticle

Study on the Tribological Properties of Porous Titanium Sliding against Tungsten Carbide YG6

by Zhiqiang Liu, Feifei Ji, Mingqiang Wang and Tianyu Zhu

Metals 2017, 7(1), 28; https://doi.org/10.3390/met7010028 - 20 Jan 2017

Cited by 12 | Viewed by 6513

Abstract

In the metal cutting process, the friction and wear behavior between the cutting tool and machined surface is the most important factor that affects the surface quality and the service life of the cutter. The irregular pore structure of porous titanium alloy has [...] Read more.

In the metal cutting process, the friction and wear behavior between the cutting tool and machined surface is the most important factor that affects the surface quality and the service life of the cutter. The irregular pore structure of porous titanium alloy has changed its mechanical properties and the processing technology. The friction and wear mechanism of the cutting tool and the machined surface is greatly different from the traditional dense metal processing because of the crumbling at the edges, tearing phenomenon and the pore agglomeration effect of chips. In this paper, the tribological characteristics and the wear mechanism of friction pair which was formed by porous titanium alloy material and hard alloy cutter were studied from cutting force, cutting speed and temperature in micro-cutting condition, and the influence of porosity on the wear rate and friction coefficient was analyzed. Results show that the main factor which influences the friction coefficient and wear rate is the porosity. The wear mechanisms of porous titanium materials were abrasive and oxidation wear while the wear mechanism of tungsten carbide YG6 was abrasive wear. The friction coefficient and wear rate of the relatively stable state are beneficial to improve the surface quality and tool life. As a result, in the micro-cutting process of porous titanium alloys, the best choice of machining parameters for different porosity materials are as follows: the load is about 8 N, the sliding speed is about 400 r/min and the temperature is about 300 °C. Full article

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13 pages, 5057 KiB

Open AccessArticle

Effects of Austenitizing Conditions on the Microstructure of AISI M42 High-Speed Steel

by Yiwa Luo, Hanjie Guo, Xiaolin Sun, Mingtao Mao and Jing Guo

Metals 2017, 7(1), 27; https://doi.org/10.3390/met7010027 - 18 Jan 2017

Cited by 46 | Viewed by 9400

Abstract

The influences of austenitizing conditions on the microstructure of AISI M42 high-speed steel were investigated through thermodynamic calculation, microstructural analysis, and in-situ observation by a confocal scanning laser microscope (CSLM). Results show that the network morphology of carbides could not dissolve completely and [...] Read more.

The influences of austenitizing conditions on the microstructure of AISI M42 high-speed steel were investigated through thermodynamic calculation, microstructural analysis, and in-situ observation by a confocal scanning laser microscope (CSLM). Results show that the network morphology of carbides could not dissolve completely and distribute equably in the case of the austenitizing temperature is 1373 K. When the austenitizing temperature reaches 1473 K, the excessive increase in temperature leads to increase in carbide dissolution, higher dissolved alloying element contents, and unwanted grain growth. Thus, 1453 K is confirmed as the best austenitizing condition on temperature for the steel. In addition, variations on the microstructure and hardness of the steel are not obvious when holding time ranges from 15 to 30 min with the austenitizing temperature of 1453 K. However, when the holding time reaches 45 min, the average size of carbides tends to increase because of Ostwald ripening. Furthermore, the value of M_s and M_f decrease with the increase of cooling rate. Hence, high cooling rate can depress the martensitic transformation and increase the content of retained austenite. As a result, the hardness of the steel is the best (65.6 HRc) when the austenitizing temperature reaches 1453 K and is held for 30 min. Full article

(This article belongs to the Special Issue Alloy Steels)

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20 pages, 11411 KiB

Open AccessArticle

The Influence of Austenite Grain Size on the Mechanical Properties of Low-Alloy Steel with Boron

by Beata Białobrzeska, Łukasz Konat and Robert Jasiński

Metals 2017, 7(1), 26; https://doi.org/10.3390/met7010026 - 17 Jan 2017

Cited by 68 | Viewed by 12528

Abstract

This study forms part of the current research on modern steel groups with higher resistance to abrasive wear. In order to reduce the intensity of wear processes, and also to minimize their impact, the immediate priority seems to be a search for a [...] Read more.

This study forms part of the current research on modern steel groups with higher resistance to abrasive wear. In order to reduce the intensity of wear processes, and also to minimize their impact, the immediate priority seems to be a search for a correlation between the chemical composition and structure of these materials and their properties. In this paper, the correlation between prior austenite grain size, martensite packets and the mechanical properties were researched. The growth of austenite grains is an important factor in the analysis of the microstructure, as the grain size has an effect on the kinetics of phase transformation. The microstructure, however, is closely related to the mechanical properties of the material such as yield strength, tensile strength, elongation and impact strength, as well as morphology of occurred fracture. During the study, the mechanical properties were tested and a tendency to brittle fracture was analysed. The studies show big differences of the analysed parameters depending on the applied heat treatment, which should provide guidance to users to specific applications of this type of steel. Full article

(This article belongs to the Special Issue Alloy Steels)

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11 pages, 3684 KiB

Open AccessArticle

Effect of Heavy Ion Irradiation Dosage on the Hardness of SA508-IV Reactor Pressure Vessel Steel

by Xue Bai, Sujun Wu, Peter K. Liaw, Lin Shao and Jonathan Gigax

Metals 2017, 7(1), 25; https://doi.org/10.3390/met7010025 - 14 Jan 2017

Cited by 18 | Viewed by 6021

Abstract

Specimens of the SA508-IV reactor pressure vessel (RPV) steel, containing 3.26 wt. % Ni and just 0.041 wt. % Cu, were irradiated at 290 °C to different displacement per atom (dpa) with 3.5 MeV Fe ions (Fe²⁺). Microstructure observation and nano-indentation [...] Read more.

Specimens of the SA508-IV reactor pressure vessel (RPV) steel, containing 3.26 wt. % Ni and just 0.041 wt. % Cu, were irradiated at 290 °C to different displacement per atom (dpa) with 3.5 MeV Fe ions (Fe²⁺). Microstructure observation and nano-indentation hardness measurements were carried out. The Continuous Stiffness Measurement (CSM) of nano-indentation was used to obtain the indentation depth profile of nano-hardness. The curves showed a maximum nano-hardness and a plateau damage near the surface of the irradiated samples, attributed to different hardening mechanisms. The Nix-Gao model was employed to analyze the nano-indentation test results. It was found that the curves of nano-hardness versus the reciprocal of indentation depth are bilinear. The nano-hardness value corresponding to the inflection point of the bilinear curve may be used as a parameter to describe the ion irradiation effect. The obvious entanglement of the dislocations was observed in the 30 dpa sample. The maximum nano-hardness values show a good linear relationship with the square root of the dpa. Full article

(This article belongs to the Special Issue Radiation Effects in Metals)

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16 pages, 5059 KiB

Open AccessArticle

One-Dimensional Constitutive Model for Porous Titanium Alloy at Various Strain Rates and Temperatures

by Zhiqiang Liu, Feifei Ji, Mingqiang Wang and Tianyu Zhu

Metals 2017, 7(1), 24; https://doi.org/10.3390/met7010024 - 12 Jan 2017

Cited by 7 | Viewed by 5798

Abstract

In this paper, the accurate description of the relationship between flow stress and strain of porous titanium alloys at various strain rates and temperatures were investigated with dynamic and quasistatic uniaxial compression tests for a further study on the processing mechanism of porous [...] Read more.

In this paper, the accurate description of the relationship between flow stress and strain of porous titanium alloys at various strain rates and temperatures were investigated with dynamic and quasistatic uniaxial compression tests for a further study on the processing mechanism of porous titanium material. Changes in their plastic flows were described through the one-dimensional Drucker-Prager (DP) constitutive model. Porous titanium alloys were micromilled in a DP simulation. After all parameters had been obtained in the DP model, the experimental and simulated true stress-strain curves and flow stress levels of two porous titanium alloys were compared to estimate the precision of the model. The findings were as follows. First, porous titanium alloys show deformation patterns characterized by pore collapse-induced deformation and have strong stress-hardening effects, but the patterns did not include noticeable plastic-flow plateaus. Second, porosity strongly affects the mechanical strength, strain-rate sensitivity, and temperature sensitivity of both alloys. Third, the DP model sufficiently describes the mechanical properties of both alloys at 25–300 °C and at strain rates of 1000–3000 s⁻¹, with a deviation of 10% or lower. Full article

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17 pages, 6831 KiB

Open AccessArticle

Effect of Controlled Cooling on Microstructure and Tensile Properties of Low C Nb-Ti-Containing HSLA Steel for Construction

by Yi Fan, Qian Wang, Hongwu Liu, Tongliang Wang, Qingfeng Wang and Fucheng Zhang

Metals 2017, 7(1), 23; https://doi.org/10.3390/met7010023 - 12 Jan 2017

Cited by 7 | Viewed by 5502

Abstract

The thermo-mechanical control processing (TMCP) of low carbon (C) Nb-Ti-containing HSLA steel with different cooling rates from 5 to 20 °C/s was simulated using a Gleeble 3500 system. The samples’ microstructure was characterized and the tensile properties measured. The results show that a [...] Read more.

The thermo-mechanical control processing (TMCP) of low carbon (C) Nb-Ti-containing HSLA steel with different cooling rates from 5 to 20 °C/s was simulated using a Gleeble 3500 system. The samples’ microstructure was characterized and the tensile properties measured. The results show that a microstructure mainly consisting of quasi-polygonal ferrite (QPF), granular bainitic ferrite (GBF), and martensite/austenite (M/A) constituent formed in each sample. Furthermore, the accelerated cooling led to a significant grain refinement of the QPF and GBF, and an increase in the density of dislocations, as well as suppressed the precipitation of nanoscale particles; however, the overall yield strength (YS) still increased obviously. The accelerated cooling also brought about a decrease in amount of M/A constituent acting as a mixed hard phase, which weakened the overall strain-hardening capacity of the QPF + GBF + M/A multiphase steel and simultaneously elevated yield-to-tensile strength ratio (YR). In addition, the mechanisms in dominating the influence of controlled cooling on the final microstructure and tensile properties were discussed. Full article

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11 pages, 5040 KiB

Open AccessArticle

The Effect of Diffusion Welding Parameters on the Mechanical Properties of Titanium Alloy and Aluminum Couples

by Enes Akca and Ali Gursel

Metals 2017, 7(1), 22; https://doi.org/10.3390/met7010022 - 11 Jan 2017

Cited by 17 | Viewed by 7882

Abstract

Ti-6Al-4V alloy and commercially pure aluminum, which are commonly used in aerospace, medical, and automotive industries, are bonded by diffusion welding. Different welding parameters (560, 600, and 640 °C—0, 45, and 60 min—under argon shielding) are used in this process to make the [...] Read more.

Ti-6Al-4V alloy and commercially pure aluminum, which are commonly used in aerospace, medical, and automotive industries, are bonded by diffusion welding. Different welding parameters (560, 600, and 640 °C—0, 45, and 60 min—under argon shielding) are used in this process to make the materials more applicable in the industry. Here, the effects of parameters on the strength of joints were studied. The bonded samples were subjected to microhardness and tensile tests in order to determine their interfacial strength. The hardness values were found to decrease with increasing distance from the interface on the titanium side while it remained constant on the aluminum side. Maximum tensile strength was taken from the maximum bonding temperatures of 600 and 640 °C. A morphology examination of the diffusion interfaces was carried out with scanning electron microscopy. Full article

(This article belongs to the Special Issue Selected Papers from ICWET16)

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9 pages, 919 KiB

Open AccessArticle

Study of Adsorption of Hydrogen on Al, Cu, Mg, Ti Surfaces in Al Alloy Melt via First Principles Calculation

by Yu Liu, Yuanchun Huang, Zhengbing Xiao and Xianwei Reng

Metals 2017, 7(1), 21; https://doi.org/10.3390/met7010021 - 11 Jan 2017

Cited by 26 | Viewed by 6677

Abstract

Adsorption of hydrogen on Al(111), Cu(111), Mg(0001), and Ti(0001) surfaces have been investigated by means of first principles calculation. The calculation of surface energy indicates that Mg(0001) is the most stable surface, while Ti(0001) is the most unstable surface among all the four [...] Read more.

Adsorption of hydrogen on Al(111), Cu(111), Mg(0001), and Ti(0001) surfaces have been investigated by means of first principles calculation. The calculation of surface energy indicates that Mg(0001) is the most stable surface, while Ti(0001) is the most unstable surface among all the four calculated surfaces. The obtained adsorption energy shows that the interaction between Al and H atoms should be energetically unfavorable, and the adsorption of hydrogen on Mg(0001) surface was found to be energetically preferred. Besides, the stability of hydrogen adsorption on studied surfaces increased in the order of Al(111), Ti(0001), Cu(111), Mg(0001). Calculation results also reveal that hydrogen adsorption on fcc and hcp sites are energetically stable compared with top and bridge sites for Ti(0001), Cu(111), and Mg(0001), while hydrogen adsorbing at the top site of Al(111) is the most unstable state compared with other sites. The calculated results agreed well with results from experiments and values in other calculations. Full article

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9 pages, 233 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Metals in 2016

by Metals Editorial Office

Metals 2017, 7(1), 20; https://doi.org/10.3390/met7010020 - 11 Jan 2017

Viewed by 5010

Abstract

The editors of Metals would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2016.[...] Full article

13 pages, 3217 KiB

Open AccessArticle

Properties of Resistance Spot-Welded TWIP Steels

by Havva Kazdal Zeytin, Hayriye Ertek Emre and Ramazan Kaçar

Metals 2017, 7(1), 14; https://doi.org/10.3390/met7010014 - 11 Jan 2017

Cited by 20 | Viewed by 7737

Abstract

High manganese TWIP (twinning-induced plasticity) steels are particularly attractive for automotive applications because of their exceptional properties of strength combined with an excellent ductility. However, the microstructure and properties of TWIP steels are affected by excessive thermal cycles, such as welding and heat [...] Read more.

High manganese TWIP (twinning-induced plasticity) steels are particularly attractive for automotive applications because of their exceptional properties of strength combined with an excellent ductility. However, the microstructure and properties of TWIP steels are affected by excessive thermal cycles, such as welding and heat treatment. This paper deals with characterization and understanding the effect of welding current and time on the mechanical properties and microstructure of the resistance spot welded TWIP steel. For this purpose, weld nugget diameter was evaluated and the hardness, tensile shear strength of the weldment, and failure mode of samples were also determined. It has been found that the tensile shear strength of the samples increased with increasing welding current and welding time without expulsion, which reduces the strength of the weldment. Tensile shear samples failed by a partial interfacial fracture mode for low-heat input welds. The pullout fractures were observed with a sufficient heat input without expulsion. Full article

(This article belongs to the Special Issue Selected Papers from ICWET16)

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12 pages, 3438 KiB

Open AccessArticle

Optimization of Copper Removal from Aqueous Solutions Using Emulsion Liquid Membranes with Benzoylacetone as a Carrier

by Loreto León, Gerardo León, Javier Senent and Carmen Pérez-Sirvent

Metals 2017, 7(1), 19; https://doi.org/10.3390/met7010019 - 10 Jan 2017

Cited by 15 | Viewed by 4510

Abstract

The presence of heavy metals in aqueous solutions above certain limits represents a serious threat to the environment due to their toxicity and non-degradability. Thus, the removal of these metals from contaminated waters has received increasing attention during recent decades. This paper describes [...] Read more.

The presence of heavy metals in aqueous solutions above certain limits represents a serious threat to the environment due to their toxicity and non-degradability. Thus, the removal of these metals from contaminated waters has received increasing attention during recent decades. This paper describes the removal of Cu(II) from aqueous solutions by emulsion liquid membranes, through a carrier-facilitated counter-transport mechanism, using benzoylacetone as the carrier and HCl as the stripping agent (protons as counter-ions). To optimize the Cu(II) removal process, the effect of the following operating parameters on the on the stability of the emulsion liquid membrane and on the Cu(II) removal efficiency was studied: feed pH, HCl concentration in the permeate phase, carrier and emulsifier concentration in the membrane phase, feed phase/emulsion phase and permeate phase/membrane phase volume ratios, emulsification time and speed in the primary emulsion preparation and stirring speed in the whole feed phase/emulsion phase system. Typical membrane transport parameters, such as flux and permeability, were also determined. Optimal Cu(II) removal conditions were: 5.5 feed pH, 10 kg/m³ benzoylacetone concentration in the membrane phase, 18.250 kg/m³ HCl concentration in the permeate phase, 50 kg/m³ Span 80 concentration in the membrane phase, 200 rpm stirring rate, 5 min emulsification time, 2700 rpm emulsification rate, 2:1 feed:emulsion volume ratio and 1:1 permeate:membrane volume ratio. In these optimal conditions, 80.3% of Cu(II) was removed in 15 min with an apparent initial flux and permeability of 0.3384 kg·m⁻³·min⁻¹ and 0.3208 min⁻¹, respectively. Full article

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12 pages, 4329 KiB

Open AccessFeature PaperArticle

The Al Effects of Co-Free and V-Containing High-Entropy Alloys

by Songqin Xia, Xiao Yang, Mingbiao Chen, Tengfei Yang and Yong Zhang

Metals 2017, 7(1), 18; https://doi.org/10.3390/met7010018 - 10 Jan 2017

Cited by 14 | Viewed by 6458

Abstract

In this study, five-component high-entropy alloys (HEAs) Al_xCrFeNiV (where x denotes the molar ratio, x = 0, 0.1, 0.3, 0.5, 0.75, 1, and 1.5) were prepared using an arc-melting furnace. The effects of the addition of the Al on the crystal [...] Read more.

In this study, five-component high-entropy alloys (HEAs) Al_xCrFeNiV (where x denotes the molar ratio, x = 0, 0.1, 0.3, 0.5, 0.75, 1, and 1.5) were prepared using an arc-melting furnace. The effects of the addition of the Al on the crystal structures were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Also, two non-equiatomic ratio HEAs, Al_xCrFeNiV (x = 0.3, and 0.5), were systematically studied through the use of various characterization methods in the as-cast state. The Al_0.3CrFeNiV alloy displayed typical duplex body-centered cubic (BCC) structures, including disordered BCC (A2), and NiAl-type ordered BCC (B2) phases. Meanwhile, in regard to the Al_0.5CrFeNiV alloy, this alloy was found to contain an unknown phase which was enriched in Cr and V, as well as the coherent A2/B2 phases. Both of these alloys displayed very high yield and fracture strengths. However, their compression fracture strains were approximately 10%. Also, the fracture surfaces showed mainly cleavage fracture modes. Full article

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15 pages, 1383 KiB

Open AccessArticle

Evaluation of Methods for Estimation of Cyclic Stress-Strain Parameters from Monotonic Properties of Steels

by Tea Marohnić, Robert Basan and Marina Franulović

Metals 2017, 7(1), 17; https://doi.org/10.3390/met7010017 - 7 Jan 2017

Cited by 15 | Viewed by 6022

Abstract

Most existing methods for estimation of cyclic yield stress and cyclic Ramberg-Osgood stress-strain parameters of steels from their monotonic properties were developed on relatively modest number of material datasets and without considerations of the particularities of different steel subgroups formed according to their [...] Read more.

Most existing methods for estimation of cyclic yield stress and cyclic Ramberg-Osgood stress-strain parameters of steels from their monotonic properties were developed on relatively modest number of material datasets and without considerations of the particularities of different steel subgroups formed according to their chemical composition (unalloyed, low-alloy, and high-alloy steels) or delivery, i.e., testing condition. Furthermore, some methods were evaluated using the same datasets that were used for their development. In this paper, a comprehensive statistical analysis and evaluation of existing estimation methods were performed using an independent set of experimental material data compriseding 116 steels. Results of performed statistical analyses reveal that statistically significant differences exist among unalloyed, low-alloy, and high-alloy steels regarding their cyclic yield stress and cyclic Ramberg-Osgood stress-strain parameters. Therefore, estimation methods were evaluated separately for mentioned steel subgroups in order to more precisely determine their applicability for the estimation of cyclic behavior of steels belonging to individual subgroups. Evaluations revealed that considering all steels as a single group results in averaging and that subgroups should be treated independently. Based on results of performed statistical analysis, guidelines are provided for identification and selection of suitable methods to be applied for the estimation of cyclic stress-strain parameters of steels. Full article

(This article belongs to the Special Issue Fatigue Damage)

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10 pages, 2366 KiB

Open AccessFeature PaperArticle

Vibration-Assisted Sputter Coating of Cenospheres: A New Approach for Realizing Cu-Based Metal Matrix Syntactic Foams

by Andrei Shishkin, Maria Drozdova, Viktor Kozlov, Irina Hussainova and Dirk Lehmhus

Metals 2017, 7(1), 16; https://doi.org/10.3390/met7010016 - 7 Jan 2017

Cited by 36 | Viewed by 7320

Abstract

The coating of hollow alumino-silicate microspheres or cenospheres with thin layers of Cu by means of vibration-assisted magnetron sputtering yields a starting material with considerable potential for the production of new types of metal matrix syntactic foams as well as optimized variants of [...] Read more.

The coating of hollow alumino-silicate microspheres or cenospheres with thin layers of Cu by means of vibration-assisted magnetron sputtering yields a starting material with considerable potential for the production of new types of metal matrix syntactic foams as well as optimized variants of conventional materials of this kind. This study introduces the coating process and the production of macroscopic samples from the coated spheres via spark plasma sintering (SPS). The influence of processing parameters on the coating itself, and the syntactic foams are discussed in terms of the obtained density levels as a function of sintering temperature (which was varied between 850 and 1080 °C), time (0.5 to 4 min), and surface appearance before and after SPS treatment. Sintering temperatures of 900 °C and above were found to cause breaking-up of the homogeneous sputter coating into a net-like structure. This effect is attributed to wetting behavior of Cu on the alumino-silicate cenosphere shells. Cylindrical samples were subjected to conductivity measurements and mechanical tests, and the first performance characteristics are reported here. Compressive strengths for Cu-based materials in the density range of 0.90–1.50 g/cm³ were found to lie between 8.6 and 61.9 MPa, depending on sintering conditions and density. An approximate relationship between strength and density is suggested based on the well-known Gibson–Ashby law. Density-related strength of the new material is contrasted to similar findings for several types of established metal foams gathered from the literature. Besides discussing these first experimental results, this paper outlines the potential of coated microspheres as optimized filler particles in metal matrix syntactic foams, and suggests associated directions of future research. Full article

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12 pages, 2113 KiB

Open AccessArticle

A Meso-Mechanical Constitutive Model of Particle-Reinforced Titanium Matrix Composites at High Temperatures

by Weidong Song, Liansong Dai, Lijun Xiao, Cheng Wang, Xiaonan Mao and Huiping Tang

Metals 2017, 7(1), 15; https://doi.org/10.3390/met7010015 - 7 Jan 2017

Cited by 4 | Viewed by 4600

Abstract

The elastoplastic properties of TiC particle-reinforced titanium matrix composites (TiC/TMCs) at high temperatures were examined by quasi-static tensile experiments. The specimens were stretched at 300 °C, 560 °C, and 650 °C, respectively at a strain rate of 0.001/s. scanning electron microscope (SEM) observation [...] Read more.

The elastoplastic properties of TiC particle-reinforced titanium matrix composites (TiC/TMCs) at high temperatures were examined by quasi-static tensile experiments. The specimens were stretched at 300 °C, 560 °C, and 650 °C, respectively at a strain rate of 0.001/s. scanning electron microscope (SEM) observation was carried out to reveal the microstructure of each specimen tested at different temperatures. The mechanical behavior of TiC/TMCs was analyzed by considering interfacial debonding afterwards. Based on Eshelby’s equivalent inclusion theory and Mori-Tanaka’s concept of average stress in the matrix, the stress or strain of the matrix, the particles, and the effective stiffness tensor of the composite were derived under prescribed traction boundary conditions at high temperatures. The plastic strains due to the thermal mismatch between the matrix and the reinforced particles were considered as eigenstrains. The interfacial debonding was calculated by the tensile strength of the particles and debonding probability was described by Weibull distribution. Finally, a meso-mechanical constitutive model was presented to explore the high-temperature elastoplastic properties of the spherical particle-reinforced titanium matrix composites by using a secant modulus method for the interfacial debonding. Full article

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

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11 pages, 4929 KiB

Open AccessArticle

Effect of a Minor Sr Modifier on the Microstructures and Mechanical Properties of 7075 T6 Al Alloys

by Shaoming Ma, Youhong Sun, Huiyuan Wang, Xiaoshu Lü, Ming Qian, Yinlong Ma, Chi Zhang and Baochang Liu

Metals 2017, 7(1), 13; https://doi.org/10.3390/met7010013 - 6 Jan 2017

Cited by 12 | Viewed by 7258

Abstract

The influence of a minor strontium (Sr) modifier on the microstructures and mechanical properties of 7075 Al alloys was investigated in this paper. The grain size of cast 7075 Al alloys was refined from 157 μm to 115 μm, 108 μm, and 105 [...] Read more.

The influence of a minor strontium (Sr) modifier on the microstructures and mechanical properties of 7075 Al alloys was investigated in this paper. The grain size of cast 7075 Al alloys was refined from 157 μm to 115 μm, 108 μm, and 105 μm after adding 0.05 wt. %, 0.1 wt. %, and 0.2 wt. % Sr, respectively. The extruded 7075 Al alloys was refined with different degrees of Sr modifier. The mechanical properties were optimum when adding 0.1 wt. % Sr. The ultimate tensile strength (σ_b) increased from 573 to 598 MPa and the elongation-to-failure (δ_f) was raised from 19.5% to 24.9%. The microhardness increased from 182 to 195 Hv. The tensile fracture surface via scanning electron microscopy (SEM) revealed a transition from brittle fracture to ductile fracture as Sr increased from 0 wt. % to 0.2 wt. %. The result in this paper proved that the modifier can improve the properties of 7075 Al alloy. Full article

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7 pages, 2942 KiB

Open AccessArticle

Microstructural and Mechanical Characteristics of Novel 6% Cr Cold-Work Tool Steel

by Singon Kang, Minwook Kim and Seok-Jae Lee

Metals 2017, 7(1), 12; https://doi.org/10.3390/met7010012 - 6 Jan 2017

Cited by 11 | Viewed by 4669

Abstract

We investigated a new cold-work tool steel with a low Cr content of 6 wt. % which was designed based on thermodynamic calculation to minimize the formation of primary carbide. A smaller particle size and a smaller volume fraction of carbides were observed [...] Read more.

We investigated a new cold-work tool steel with a low Cr content of 6 wt. % which was designed based on thermodynamic calculation to minimize the formation of primary carbide. A smaller particle size and a smaller volume fraction of carbides were observed in this 6% Cr steel. Superior mechanical properties in terms of hardness, impact toughness, tensile strength, and total elongation were achieved in this steel, due to fine secondary carbides precipitated during tempering. These carbide particles were M₆C and (Mo,V)C carbides with a diameter below 100 nm. Full article

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8 pages, 7974 KiB

Open AccessFeature PaperArticle

A Study on the Aging Behavior of Al6061 Composites Reinforced with Y₂O₃ and TiC

by Chun-Liang Chen and Chen-Han Lin

Metals 2017, 7(1), 11; https://doi.org/10.3390/met7010011 - 4 Jan 2017

Cited by 16 | Viewed by 5546

Abstract

The reinforcement particles play important roles in determining microstructural development and properties of Al6061 composites. In the present work, the aging behavior of Al6061 reinforced with Y₂O₃ and TiC particles produced via mechanical alloying are investigated. The results indicate that [...] Read more.

The reinforcement particles play important roles in determining microstructural development and properties of Al6061 composites. In the present work, the aging behavior of Al6061 reinforced with Y₂O₃ and TiC particles produced via mechanical alloying are investigated. The results indicate that the peak-aged Al6061 alloy without reinforcement demonstrates the highest hardness, which corresponds to the formation of the Mg–Si precipitates. However, precipitation formation is not observed in the case of the Al6061 composites, which can be attributed to the fact that the Mg–Si clusters and GP zones are inhibited by the presence of the reinforcement particles. The solute elements segregate in the complex oxides or carbides and contribute to only a slight increase in hardness. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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10 pages, 2983 KiB

Open AccessArticle

The Improvement of Dehydriding the Kinetics of NaMgH₃ Hydride via Doping with Carbon Nanomaterials

by Zhong-Min Wang, Song Tao, Jia-Jun Li, Jian-Qiu Deng, Huaiying Zhou and Qingrong Yao

Metals 2017, 7(1), 9; https://doi.org/10.3390/met7010009 - 30 Dec 2016

Cited by 16 | Viewed by 4596

Abstract

NaMgH₃ perovskite hydride and NaMgH₃–carbon nanomaterials (NH-CM) composites were prepared via the reactive ball-milling method. To investigate the catalytic effect of CM on the dehydriding kinetic properties of NaMgH₃ hydride, multiwall carbon nanotubes (MWCNTs) and graphene oxide (GO) were [...] Read more.

NaMgH₃ perovskite hydride and NaMgH₃–carbon nanomaterials (NH-CM) composites were prepared via the reactive ball-milling method. To investigate the catalytic effect of CM on the dehydriding kinetic properties of NaMgH₃ hydride, multiwall carbon nanotubes (MWCNTs) and graphene oxide (GO) were used as catalytic additives. It was found that dehydriding temperatures and activation energies (ΔE₁ and ΔE₂) for two dehydrogenation steps of NaMgH₃ hydride can be greatly reduced with a 5 wt. % CM addition. The NH–2.5M–2.5G composite presents better dehydriding kinetics, a lower dehydriding temperature, and a higher hydrogen-desorbed amount (3.64 wt. %, 638 K). ΔE₁ and ΔE₂ can be reduced by about 67 kJ/mol and 30 kJ/mol, respectively. The results suggest that the combination of MWCNTs and GO is a better catalyst as compared to MWCNTs or GO alone. Full article

(This article belongs to the Special Issue Metal Hydrides)

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12 pages, 5210 KiB

Open AccessArticle

Microstructures and Properties Evolution of Al-Cu-Mn Alloy with Addition of Vanadium

by Fansheng Meng, Zhi Wang, Yuliang Zhao, Datong Zhang and Weiwen Zhang

Metals 2017, 7(1), 10; https://doi.org/10.3390/met7010010 - 30 Dec 2016

Cited by 21 | Viewed by 6869

Abstract

The effect of the vanadium addition on the microstructure, the precipitation behavior, and the mechanical properties of the Al-5.0Cu-0.4Mn alloy has been studied. The as-cast Al-5.0Cu-0.4Mn alloy was produced by squeeze casting and the heat treatment was carried out following the standard T6 [...] Read more.

The effect of the vanadium addition on the microstructure, the precipitation behavior, and the mechanical properties of the Al-5.0Cu-0.4Mn alloy has been studied. The as-cast Al-5.0Cu-0.4Mn alloy was produced by squeeze casting and the heat treatment was carried out following the standard T6 treatment. It is shown that, with the addition of V, grain refinement of aluminum occurred. During heat treatment, the addition of V accelerates the precipitation kinetics of θ′ (Al₂Cu) phase along the grain boundaries, and promotes the growth rate of the θ′ in the α(Al) matrix. Meanwhile, the addition of V retards the precipitation of T (Al₂₀Cu₂Mn₃) phase. The tensile strength of the Al-5.0Cu-0.4Mn alloy increases with the increase of V content, which can be explained by combined effects of the solid solution strengthening and precipitate strengthening. However, excessively high V addition deteriorates the mechanical properties by forming brittle coarse intermetallic phases. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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7 pages, 2841 KiB

Open AccessArticle

The Morphologies of Different Types of Fe₂SiO₄–FeO in Si-Containing Steel

by Mingxing Zhou, Guang Xu, Haijiang Hu, Qing Yuan and Junyu Tian

Metals 2017, 7(1), 8; https://doi.org/10.3390/met7010008 - 29 Dec 2016

Cited by 11 | Viewed by 4958

Abstract

Red scale defect is known to be mainly caused by net-like Fe₂SiO₄–FeO. In the present study, the morphology of Fe₂SiO₄–FeO in a Si-containing steel was investigated by simultaneous thermal analysis, high-temperature laser scanning confocal microscopy, [...] Read more.

Red scale defect is known to be mainly caused by net-like Fe₂SiO₄–FeO. In the present study, the morphology of Fe₂SiO₄–FeO in a Si-containing steel was investigated by simultaneous thermal analysis, high-temperature laser scanning confocal microscopy, scanning electron microscopy, and energy dispersive spectroscopy. Only liquid Fe₂SiO₄–FeO can form a net-like morphology. Liquid Fe₂SiO₄–FeO is classified into two types in this work. Type-1 liquid Fe₂SiO₄–FeO is formed by melting pre-existing solid Fe₂SiO₄–FeO that already exists before the melting point of Fe₂SiO₄–FeO. Type-2 liquid Fe₂SiO₄–FeO is formed at a temperature higher than the melting point of Fe₂SiO₄–FeO. The results show that type-1 liquid Fe₂SiO₄–FeO is more likely to form a net-like morphology than is type-2 liquid Fe₂SiO₄–FeO. The penetration depth of type-1 liquid Fe₂SiO₄–FeO is also larger at the same oxidation degree. Therefore, type-1 liquid Fe₂SiO₄–FeO should be avoided in order to eliminate red scale defect. Net-like Fe₂SiO₄–FeO may be alleviated by two methods: decreasing the oxygen concentration in the heating furnace before the melting point of Fe₂SiO₄–FeO is reached and increasing the reheating rate before the melting point. In addition, FeO is distributed with a punctiform or lamellar morphology on Fe₂SiO₄. Full article

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6 pages, 1258 KiB

Open AccessArticle

The Effect of Iron Content on Glass Forming Ability and Thermal Stability of Co–Fe–Ni–Ta–Nb–B–Si Bulk Metallic Glass

by Aytekin Hitit and Hakan Şahin

Metals 2017, 7(1), 7; https://doi.org/10.3390/met7010007 - 29 Dec 2016

Cited by 6 | Viewed by 5492

Abstract

In this study, change in glass forming ability (GFA) and thermal stability of Co–Fe-based bulk metallic glasses were investigated as a function of iron content. Cylindrical samples of alloys with diameters of up to 4 mm were synthesized by a suction casting method [...] Read more.

In this study, change in glass forming ability (GFA) and thermal stability of Co–Fe-based bulk metallic glasses were investigated as a function of iron content. Cylindrical samples of alloys with diameters of up to 4 mm were synthesized by a suction casting method in an arc furnace. Structures and thermal properties of the as-cast samples were determined by X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. It was found that the critical casting thickness of the alloys reduced as iron content was increased and cobalt content was decreased. It was determined that GFA parameters, reduced glass transition temperature (T_g/T_l) and δ (= T_x/(T_l − T_g)), show a very good correlation with critical casting thickness values. It was also observed that changing iron content did not effect thermal properties of the alloys. Full article

(This article belongs to the Special Issue Bulk Metallic Glasses)

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9 pages, 2920 KiB

Open AccessArticle

A Case Study for the Welding of Dissimilar EN AW 6082 and EN AW 5083 Aluminum Alloys by Friction Stir Welding

by Sefika Kasman, Fatih Kahraman, Anıl Emiralioğlu and Haydar Kahraman

Metals 2017, 7(1), 6; https://doi.org/10.3390/met7010006 - 29 Dec 2016

Cited by 15 | Viewed by 6640

Abstract

The aim of this study is to investigate the effect of keeping constant the tool rotational speed to the welding speed ratio (υ ratio) on the mechanical properties of the dissimilar friction stir welding of EN AW6082-T6 and EN AW5083-H111. Two different pins [...] Read more.

The aim of this study is to investigate the effect of keeping constant the tool rotational speed to the welding speed ratio (υ ratio) on the mechanical properties of the dissimilar friction stir welding of EN AW6082-T6 and EN AW5083-H111. Two different pins shaped as triangular and pentagonal were associated with the constant υ ratio. From the tensile test results, it was found that the υ ratio does not create an evident change in the weld joint strength. The small cavity- and tunnel-type defects were observed at the nugget zone and located on the advancing side of the pin. These defects caused a decrease in the strength and elongation of the weld joint. The most important inference obtained from the experimental results is that if the υ ratio is kept constant, the weld joint strength for each weld does not correspond to a constant value. Full article

(This article belongs to the Special Issue Selected Papers from ICWET16)

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12 pages, 3576 KiB

Open AccessArticle

Microstructure, Residual Stress, Corrosion and Wear Resistance of Vacuum Annealed TiCN/TiN/Ti Films Deposited on AZ31

by Haitao Li, Shoufan Rong, Pengfei Sun and Qiang Wang

Metals 2017, 7(1), 5; https://doi.org/10.3390/met7010005 - 29 Dec 2016

Cited by 11 | Viewed by 5019

Abstract

Composite titanium carbonitride (TiCN) thin films deposited on AZ31 by DC/RF magnetron sputtering were vacuum annealed at different temperatures. Vacuum annealing yields the following on the structure and properties of the films: the grain grows and the roughness increases with an increase of [...] Read more.

Composite titanium carbonitride (TiCN) thin films deposited on AZ31 by DC/RF magnetron sputtering were vacuum annealed at different temperatures. Vacuum annealing yields the following on the structure and properties of the films: the grain grows and the roughness increases with an increase of annealing temperature, the structure changes from polycrystalline to single crystal, and the distribution of each element becomes more uniform. The residual stress effectively decreases compared to the as-deposited film, and their corrosion resistance is much improved owing to the change of structure and fusion of surface defects, whereas the wear-resistance is degraded due to the grain growth and the increase of surface roughness under a certain temperature. Full article

(This article belongs to the Special Issue Corrosion of Magnesium Alloys)

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18 pages, 3552 KiB

Open AccessArticle

Mathematical Modeling of the Concentrated Energy Flow Effect on Metallic Materials

by Sergey Konovalov, Xizhang Chen, Vladimir Sarychev, Sergey Nevskii, Victor Gromov and Milan Trtica

Metals 2017, 7(1), 4; https://doi.org/10.3390/met7010004 - 27 Dec 2016

Cited by 40 | Viewed by 5369

Abstract

Numerous processes take place in materials under the action of concentrated energy flows. The most important ones include heating together with the temperature misdistribution throughout the depth, probable vaporization on the surface layer, melting to a definite depth, and hydrodynamic flotation; generation of [...] Read more.

Numerous processes take place in materials under the action of concentrated energy flows. The most important ones include heating together with the temperature misdistribution throughout the depth, probable vaporization on the surface layer, melting to a definite depth, and hydrodynamic flotation; generation of thermo-elastic waves; dissolution of heterogeneous matrix particles; and formation of nanolayers. The heat-based model is presented in an enthalpy statement involving changes in the boundary conditions, which makes it possible to consider melting and vaporization on the material surface. As a result, a linear dependence of penetration depth vs. energy density has been derived. The model of thermo-elastic wave generation is based on the system of equations on the uncoupled one-dimensional problem of dynamic thermo-elasticity for a layer with the finite thickness. This problem was solved analytically by the symbolic method. It has been revealed for the first time that the generated stress pulse comprises tension and compression zones, which are caused by increases and decreases in temperature on the boundary. The dissolution of alloying elements is modeled on the example of a titanium-carbon system in the process of electron beam action. The mathematical model is proposed to describe it, and a procedure is suggested to solve the problem of carbon distribution in titanium carbide and liquid titanium-carbide solution in terms of the state diagram and temperature changes caused by phase transitions. Carbon concentration vs. spatial values were calculated for various points of time at diverse initial temperatures of the cell. The dependence of carbon particle dissolution on initial temperature and radius of the particle were derived. A hydrodynamic model based on the evolution of Kelvin-Helmholtz instability in shear viscous flows has been proposed to specify the formation of nanostructures in materials subjected to the action of concentrated energy flows. It has been pointed out for the first time that, for certain parameters of the problem, that there are two micro- and nanoscale peaks in the relation of the decrement to the wavelength of the interface disturbance. Full article

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10 pages, 3781 KiB

Open AccessArticle

Properties of Mechanically Alloyed W-Ti Materials with Dual Phase Particle Dispersion

by František Lukáč, Monika Vilémová, Barbara Nevrlá, Jakub Klečka, Tomáš Chráska and Orsolya Molnárová

Metals 2017, 7(1), 3; https://doi.org/10.3390/met7010003 - 26 Dec 2016

Cited by 10 | Viewed by 5526

Abstract

W alloys are currently widely studied materials for their potential application in future fusion reactors. In the presented study, we report on the preparation and properties of mechanically alloyed W-Ti powders compacted by pulsed electric current sintering. Four different powder compositions of W-(3%–7%)Ti [...] Read more.

W alloys are currently widely studied materials for their potential application in future fusion reactors. In the presented study, we report on the preparation and properties of mechanically alloyed W-Ti powders compacted by pulsed electric current sintering. Four different powder compositions of W-(3%–7%)Ti with Hf or HfC were prepared. The alloys’ structure contains only high-melting-point phases, namely the W-Ti matrix, complex carbide (Ti,W,Hf)C and HfO₂ particle dispersion; Ti in the form of a separate phase is not present. The bending strength of the alloys depends on the amount of Ti added. The addition of 3 wt. % Ti led to an increase whereas 7 wt. % Ti led to a major decrease in strength when compared to unalloyed tungsten sintered at similar conditions. The addition of Ti significantly lowered the room-temperature thermal conductivity of all prepared materials. However, unlike pure tungsten, the conductivity of the prepared alloys increased with the temperature. Thus, the thermal conductivity of the alloys at 1300 °C approached the value of the unalloyed tungsten. Full article

(This article belongs to the Special Issue Mechanical Alloying)

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35 pages, 6938 KiB

Open AccessFeature PaperReview

Selective Laser Melting of Magnesium and Magnesium Alloy Powders: A Review

by Vyasaraj Manakari, Gururaj Parande and Manoj Gupta

Metals 2017, 7(1), 2; https://doi.org/10.3390/met7010002 - 26 Dec 2016

Cited by 211 | Viewed by 22404

Abstract

Magnesium-based materials are used primarily in developing lightweight structures owing to their lower density. Further, being biocompatible they offer potential for use as bioresorbable materials for degradable bone replacement implants. The design and manufacture of complex shaped components made of magnesium with good [...] Read more.

Magnesium-based materials are used primarily in developing lightweight structures owing to their lower density. Further, being biocompatible they offer potential for use as bioresorbable materials for degradable bone replacement implants. The design and manufacture of complex shaped components made of magnesium with good quality are in high demand in the automotive, aerospace, and biomedical areas. Selective laser melting (SLM) is becoming a powerful additive manufacturing technology, enabling the manufacture of customized, complex metallic designs. This article reviews the recent progress in the SLM of magnesium based materials. Effects of SLM process parameters and powder properties on the processing and densification of the magnesium alloys are discussed in detail. The microstructure and metallurgical defects encountered in the SLM processed parts are described. Applications of SLM for potential biomedical applications in magnesium alloys are also addressed. Finally, the paper summarizes the findings from this review together with some proposed future challenges for advancing the knowledge in the SLM processing of magnesium alloy powders. Full article

(This article belongs to the Special Issue 3D Printing of Metals)

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