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Metals, Volume 10, Issue 8 (August 2020) – 124 articles

Cover Story (view full-size image): The determination of three components of displacement at material surfaces is possible using surface topography information. The height digital image correlation (hDIC) technique was developed as a full field method for this purpose and demonstrated micro-level in-plane resolution and nanoscale out-of-plane precision. The subsequent use of integer-pixel and sub-pixel level correlation stages of the hDIC technique combined with an intermediate step identifies triaxial displacements at emerging discontinuities without the requirement for additional guiding procedures. The high computational demand of this process was tackled using the graphics processing unit (GPU) parallel computing capability with the paging approach. View this paper.
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Article
The Forming Control Method of Multi-Track Laser Cladding on Curved Surface
Metals 2020, 10(8), 1109; https://doi.org/10.3390/met10081109 - 18 Aug 2020
Cited by 3 | Viewed by 957
Abstract
This paper investigated the correlation between the processing parameters and the properties of clad deposited by laser cladding on a curved surface. Mathematical models relating the processing parameters (laser power, scanning speed, gas flow, and overlap ratio) and clad properties (flatness ratio and [...] Read more.
This paper investigated the correlation between the processing parameters and the properties of clad deposited by laser cladding on a curved surface. Mathematical models relating the processing parameters (laser power, scanning speed, gas flow, and overlap ratio) and clad properties (flatness ratio and pore area) were established by central composite design. Analysis of variance and experimental validation confirmed the validity of the models. The results indicated that the flatness ratio was negatively influenced by the larger scanning speed, gas flow, and overlap ratio, while the pore area was enlarged by the increasing of scanning speed, and increasing the overlap ratio lead to the pore area reducing at first and then increasing. Optimized processing parameters were obtained under the target of maximizing the flatness ratio and minimizing the pore area. The developed mathematical models enabled predicting the flatness ratio and pore area with optimized processing parameters. The validation experimental result verified the prediction accuracy of the models and displayed target improvement compared with the original central composite design. The results provide theoretical guidance in multi-track laser cladding on a curved surface for the prediction and control of the geometric characteristics of the coating and the optimization of the processing parameters. This research outcome provides guidance for the coating deposition application in crankshaft surface coating or surface restoration, rotary parts coating deposition, or complex shape tool manufacturing. It also forms the fundamental basis for the extensive application of multi-track laser cladding on curved substrates in the additive manufacturing industry. Full article
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Article
Particle Ejection by Jetting and Related Effects in Impact Welding Processes
Metals 2020, 10(8), 1108; https://doi.org/10.3390/met10081108 - 18 Aug 2020
Cited by 11 | Viewed by 1261
Abstract
Collision welding processes are accompanied by the ejection of a metal jet, a cloud of particles (CoP), or both phenomena, respectively. The purpose of this study is to investigate the formation, the characteristics as well as the influence of the CoP on weld [...] Read more.
Collision welding processes are accompanied by the ejection of a metal jet, a cloud of particles (CoP), or both phenomena, respectively. The purpose of this study is to investigate the formation, the characteristics as well as the influence of the CoP on weld formation. Impact welding experiments on three different setups in normal ambient atmosphere and under vacuum-like conditions are performed and monitored using a high-speed camera, accompanied by long-term exposures, recordings of the emission spectrum, and an evaluation of the CoP interaction with witness pins made of different materials. It was found that the CoP formed during the collision of the joining partners is compressed by the closing joining gap and particularly at small collision angles it can reach temperatures sufficient to melt the surfaces to be joined. This effect was proved using a tracer material that is detectable on the witness pins after welding. The formation of the CoP is reduced with increasing yield strength of the material and the escape of the CoP is hindered with increasing surface roughness. Both effects make welding with low-impact velocities difficult, whereas weld formation is facilitated using smooth surfaces and a reduced ambient pressure under vacuum-like conditions. Furthermore, the absence of surrounding air eases the process observation since exothermic oxidation reactions and shock compression of the gas are avoided. This also enables an estimation of the temperature in the joining gap, which was found to be more than 5600 K under normal ambient pressure. Full article
(This article belongs to the Special Issue Impact Welding of Materials)
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Review
Industrial Recycling of Lithium-Ion Batteries—A Critical Review of Metallurgical Process Routes
Metals 2020, 10(8), 1107; https://doi.org/10.3390/met10081107 - 18 Aug 2020
Cited by 36 | Viewed by 6731
Abstract
Research for the recycling of lithium-ion batteries (LIBs) started about 15 years ago. In recent years, several processes have been realized in small-scale industrial plants in Europe, which can be classified into two major process routes. The first one combines pyrometallurgy with subsequent [...] Read more.
Research for the recycling of lithium-ion batteries (LIBs) started about 15 years ago. In recent years, several processes have been realized in small-scale industrial plants in Europe, which can be classified into two major process routes. The first one combines pyrometallurgy with subsequent hydrometallurgy, while the second one combines mechanical processing, often after thermal pre-treatment, with metallurgical processing. Both process routes have a series of advantages and disadvantages with respect to legislative and health, safety and environmental requirements, possible recovery rates of the components, process robustness, and economic factors. This review critically discusses the current status of development, focusing on the metallurgical processing of LIB modules and cells. Although the main metallurgical process routes are defined, some issues remain unsolved. Most process routes achieve high yields for the valuable metals cobalt, copper, and nickel. In comparison, lithium is only recovered in few processes and with a lower yield, albeit a high economic value. The recovery of the low value components graphite, manganese, and electrolyte solvents is technically feasible but economically challenging. The handling of organic and halogenic components causes technical difficulties and high costs in all process routes. Therefore, further improvements need to be achieved to close the LIB loop before high amounts of LIB scrap return. Full article
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Communication
Influence of Annealing Temperature on Corrosion Resistance of TiO2 Nanotubes Grown on Ti–30Ta Alloy
Metals 2020, 10(8), 1106; https://doi.org/10.3390/met10081106 - 18 Aug 2020
Cited by 1 | Viewed by 1003
Abstract
With little success, researchers has been searching for alloys with elements such as tantalum to improve the long-term life of implants. The Ti–30Ta alloy presents an elastic modulus E = 69 GPa that is close to that of bone (E = 17–25 GPa) [...] Read more.
With little success, researchers has been searching for alloys with elements such as tantalum to improve the long-term life of implants. The Ti–30Ta alloy presents an elastic modulus E = 69 GPa that is close to that of bone (E = 17–25 GPa) than Ti cp (E = 105 GPa). In addition, nanostructure surface modification influences cell behavior and antimicrobial activity. So, this study investigates the corrosion behavior of surface modification by TiO2 nanotube grown on Ti–30Ta alloy after anodization process in the electrolyte glycerol + NH4F 0.25% at 30 V, for nine hours without annealing and annealed in 450 °C, 530 °C and 600 °C (5 °C/min). The electrochemical behavior was evaluated by three electrodes cell. The counter-electrode of graphite, reference-electrode of saturated calomel electrode and working-electrode at electrolyte of 0.15 M NaCl + 0.03 M NaF, with pH = 6 for 8000 s. The scanned region ranged from −0.8 V to values up to 3.5 V with a sweep rate 0.166 mV/s. Potentiodynamic polarization curves were obtained with a potentiostat. The sample was characterized by scanning electron microscopy (SEM) imaging, X-ray diffraction analysis (XRD) and wettability with a contact angle goniometer. We concludes from the obtained results that all treatment surfaces are hydrophilic (<90°). The surface covered with TiO2 nanotube crystallinity showed anatase phase after annealing at 450 °C, 530 °C and 600 °C; the exceptions were the anodized-without-annealing treatment and without-surface-modification alloys. The electrochemical behavior of the five groups investigated showed similar high resistance to corrosion solution under all conditions. Full article
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Review
Review on the Comparison of the Chemical Reactivity of Cyanex 272, Cyanex 301 and Cyanex 302 for Their Application to Metal Separation from Acid Media
Metals 2020, 10(8), 1105; https://doi.org/10.3390/met10081105 - 17 Aug 2020
Cited by 8 | Viewed by 1330
Abstract
Cyanex extractants, such as Cyanex 272, Cyanex 301, and Cyanex 302 have been commercialized and widely used in the extraction and separation of metal ions in hydrometallurgy. Since Cyanex 301 and Cyanex 302 are the derivatives of Cyanex 272, these extractants have similar [...] Read more.
Cyanex extractants, such as Cyanex 272, Cyanex 301, and Cyanex 302 have been commercialized and widely used in the extraction and separation of metal ions in hydrometallurgy. Since Cyanex 301 and Cyanex 302 are the derivatives of Cyanex 272, these extractants have similar functional groups. In order to understand the different extraction behaviors of these extractants, an understanding of the relationship between their structure and reactivity is important. We reviewed the physicochemical properties of these extractants, such as their solubility in water, polymerization degree, acidity strength, extraction performance of metal ions, and the interaction with diluent and other extractants on the basis of their chemical structure. Synthetic methods for these extractants were also introduced. This information is of great value in the synthesis of new kinds of extractants for the extraction of metals from a diverse medium. From the literature, the extraction and stripping characteristics of metals by Cyanex 272 and its derivatives from inorganic acids such as HCl, H2SO4, and HNO3 were also reviewed. The replacement of oxygen with sulfur in the functional groups (P = O to P = S group) has two opposing effects. One is to enhance their acidity and extractability due to an increase in the stability of metal complexes, and the other is to make the stripping of metals from the loaded Cyanex 301 difficult. Full article
(This article belongs to the Special Issue Solvent Extraction of Transition Metals)
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Article
Conductive Heating during Press Hardening by Hot Metal Gas Forming for Curved Complex Part Geometries
Metals 2020, 10(8), 1104; https://doi.org/10.3390/met10081104 - 17 Aug 2020
Cited by 5 | Viewed by 1236
Abstract
Climate targets set by the EU, including the reduction of CO2, are leading to the increased use of lightweight materials for mass production such as press hardening steels. Besides sheet metal forming for high-strength components, tubular or profile forming (Hot Metal [...] Read more.
Climate targets set by the EU, including the reduction of CO2, are leading to the increased use of lightweight materials for mass production such as press hardening steels. Besides sheet metal forming for high-strength components, tubular or profile forming (Hot Metal Gas Forming—HMGF) allows for designs that are more complex in combination with a lower weight. This paper particularly examines the application of conductive heating of the component for the combined press hardening process. The previous Finite-Element-Method (FEM)-supported design of an industry-oriented, curved component geometry allows the development of forming tools and process peripherals with a high degree of reliability. This work comprises a description regarding the functionality of the tools and the heating strategy for the curved component as well as the measurement technology used to investigate the heat distribution in the component during the conduction process. Subsequently, forming tests are carried out, material characterization is performed by hardness measurements in relevant areas of the component, and the FEM simulation is validated by comparing the resulting sheet thickness distribution to the experimental one. Full article
(This article belongs to the Special Issue Latest Hydroforming Technology of Metallic Tubes and Sheets)
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Article
Distribution Behavior of Phosphorus in 2CaO·SiO2-3CaO·P2O5 Solid Solution Phase and Liquid Slag Phase
Metals 2020, 10(8), 1103; https://doi.org/10.3390/met10081103 - 17 Aug 2020
Cited by 1 | Viewed by 966
Abstract
In this paper, the CaO-SiO2-FetO-P2O5 dephosphorization slag system during the premier and middle stage of the converter process was studied, the effect of slag composition on the distribution ratio and activity coefficient of P in the [...] Read more.
In this paper, the CaO-SiO2-FetO-P2O5 dephosphorization slag system during the premier and middle stage of the converter process was studied, the effect of slag composition on the distribution ratio and activity coefficient of P in the n·2CaO·SiO2-3CaO·P2O5 (recorded as nC2S-C3P) solid solution phase and liquid slag phase in the slag system was studied used by the high temperature experiment in laboratory, the theoretical calculation of thermodynamics, and the scanning electron microscope and the energy dispersive spectrometer (recorded as SEM/EDS). The research results show that when the FeO content in the liquid slag increases from 32.21% to 50.31%, the distribution ratio of phosphorus (recorded as LP) in the liquid slag phase increases by 3.34 times. When the binary basicity in the liquid slag increases from 1.08 to 1.64, the LP in the liquid slag phase decreases by 94.21%. In the initial slag, when the binary basicity increases from 2.0 to 3.5, the LP decreases by 70.07%. When FeO content increases from 38.00% to 51.92%, the LP increases by 6.15 times. When P2O5 content increases from 3.00% to 9.00%, the LP increased by 10.67 times. When the FeO content in the liquid slag increases from 32.21% to 50.31%, the activity coefficient of P2O5 in the liquid slag phase (recorded as γP2O5(L)) increases by 54.33 times. When the binary basicity in the liquid slag increases from 1.08 to 1.64, γP2O5(L) decreases by 99.38%. When the binary basicity increases from 2.0 to 3.5, the activity coefficient of P2O5 in the solid solution phase (recorded as γP2O5(SS)) in the solid solution phase decreases by 98.85%. When P2O5 content increases from 3.00% to 9.00%, γP2O5(SS) increases by 1.14 times. When the binary basicity decreases from 3.5 to 2.0, n decreases from 0.438 to 0.404. When the FeO content increases from 38.00% to 51.92%, n decreases from 0.477 to 0.319. When the P2O5 content increases from 3.00% to 9.00%, n decreases from 0.432 to 0.164. The decrease of binary basicity and the increase of FeO and P2O5 content in the initial slag can reduce the value of n and enrich more phosphorus in the solid solution phase. The results can not only provide a theoretical basis for industrial production, but also lay a theoretical foundation for finding more effective dephosphorization methods. Full article
(This article belongs to the Special Issue Advances in Pyrometallurgy)
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Article
High Ductility with a Homogeneous Microstructure of a Mg–Al–Zn Alloy Prepared by Cyclic Expansion Extrusion with an Asymmetrical Extrusion Cavity
Metals 2020, 10(8), 1102; https://doi.org/10.3390/met10081102 - 14 Aug 2020
Cited by 3 | Viewed by 1042
Abstract
In the current work, cyclic expansion extrusion with an asymmetrical extrusion cavity (CEE-AEC), as a relatively novel severe plastic deformation method, was applied to fabricate an AZ31B magnesium alloy plate with a size of 50 × 100 × 220 mm, and the resultant [...] Read more.
In the current work, cyclic expansion extrusion with an asymmetrical extrusion cavity (CEE-AEC), as a relatively novel severe plastic deformation method, was applied to fabricate an AZ31B magnesium alloy plate with a size of 50 × 100 × 220 mm, and the resultant microstructure, texture development, and mechanical properties were systematically investigated. A refined and homogeneous grain structure was achieved after three passes of deformation due to dynamic recrystallization. The grain refinement degree in comparison to as-cast alloys was more than ~96%. With the increasing number of CEE-AEC passes, a basal inclination texture was gradually formed, with the basal planes inclined ~45° from the transverse direction to the extrusion direction, which could be attributed to the introduction of an asymmetrical extrusion cavity that led to an increasing Schmid factor for the activation of basal <a> slip systems. The comprehensive mechanical properties were improved by successive multi-passes of CEE-AEC processing, especially due to the ductility reaching to 30.0 ± 1.3% after three passes of deformation. The competition between the grain refinement and texture modification were the main strengthening mechanisms. Full article
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Review
A Review of the Serrated-Flow Phenomenon and Its Role in the Deformation Behavior of High-Entropy Alloys
Metals 2020, 10(8), 1101; https://doi.org/10.3390/met10081101 - 13 Aug 2020
Cited by 45 | Viewed by 3482
Abstract
High-entropy alloys (HEAs) are a novel class of alloys that have many desirable properties. The serrated flow that occurs in high-entropy alloys during mechanical deformation is an important phenomenon since it can lead to significant changes in the microstructure of the alloy. In [...] Read more.
High-entropy alloys (HEAs) are a novel class of alloys that have many desirable properties. The serrated flow that occurs in high-entropy alloys during mechanical deformation is an important phenomenon since it can lead to significant changes in the microstructure of the alloy. In this article, we review the recent findings on the serration behavior in a variety of high-entropy alloys. Relationships among the serrated flow behavior, composition, microstructure, and testing condition are explored. Importantly, the mechanical-testing type (compression/tension), testing temperature, applied strain rate, and serration type for certain high-entropy alloys are summarized. The literature reveals that the serrated flow can be affected by experimental conditions such as the strain rate and test temperature. Furthermore, this type of phenomenon has been successfully modeled and analyzed, using several different types of analytical methods, including the mean-field theory formalism and the complexity-analysis technique. Importantly, the results of the analyses show that the serrated flow in HEAs consists of complex dynamical behavior. It is anticipated that this review will provide some useful and clarifying information regarding the serrated-flow mechanisms in this material system. Finally, suggestions for future research directions in this field are proposed, such as the effects of irradiation, additives (such as C and Al), the presence of nanoparticles, and twinning on the serrated flow behavior in HEAs. Full article
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Article
Effect of Ce Addition and Heat Treatment on Microstructure Evolution and Tensile Properties of Industrial A357 Cast Alloy
Metals 2020, 10(8), 1100; https://doi.org/10.3390/met10081100 - 13 Aug 2020
Cited by 3 | Viewed by 1097
Abstract
The effects of adding different Ce contents (0–0.32 wt.%) on the microstructure, mechanical properties, and fracture morphology of industrial A357 cast alloy in as-cast and T6 heat treatment were studied. The main purpose of this study is to improve the microstructure stability and [...] Read more.
The effects of adding different Ce contents (0–0.32 wt.%) on the microstructure, mechanical properties, and fracture morphology of industrial A357 cast alloy in as-cast and T6 heat treatment were studied. The main purpose of this study is to improve the microstructure stability and tensile properties of industrial A357 cast alloy. The microstructural analyses indicate that the addition of Ce causes refinement of the α-Al primary phase for the reason that the formation of intermetallic compounds containing (AlSiCeMg) elements enriches the front of the solid–liquid interface, which causes an increase in constitutional undercooling. Simultaneously, the addition of Ce also affected the characteristics of eutectic Si particles, which make its morphology change from acicular structures into fragmented and spheroidized. This is mainly due to the formation of Ce-rich precipitates during solidification, which increase the constitutional undercooling and suppress the nucleation of the eutectic Si particles, resulting in the change of eutectic Si characteristics. Moreover, the needle-like morphology of a Fe-containing intermetallic is transformed into α(AlSiFeCe) phase containing rare earth Ce when part of the Ce atoms entered β(Al5FeSi) phase compounds. The tensile properties of the modified alloys were improved in the as-cast and T6 heat treatment as a consequence of simultaneous refinement of both secondary dendrite arm spacing and grains and the improvement of eutectic Si particles and Fe-containing intermetallic morphology. The fracture surface of the modified alloy has more dimples than the unmodified alloy, which indicates that the main fracture pattern of the modified alloy is dimple fracture caused by the crack of eutectic Si particles. The optimal percentage of Ce in industrial A357 cast alloy was determined to be 0.16 wt.% according to the change of microstructures structure and mechanical properties. These experimental results provide a new basis for adding rare earth Ce to improve the performance of parts in the actual production of industrial A357 cast alloy. Full article
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Article
Basic Sulfate Precipitation of Zirconium from Sulfuric Acid Leach Solution
Metals 2020, 10(8), 1099; https://doi.org/10.3390/met10081099 - 13 Aug 2020
Cited by 10 | Viewed by 1476
Abstract
H2SO4 was ensured to be the best candidate for Zr leaching from the eudialyte. The resulting sulfuric leach solution consisted of Zr(IV), Nb(V), Hf(IV), Al(III), and Fe(III). It was found that ordinary metal hydroxide precipitation was not feasible for obtaining [...] Read more.
H2SO4 was ensured to be the best candidate for Zr leaching from the eudialyte. The resulting sulfuric leach solution consisted of Zr(IV), Nb(V), Hf(IV), Al(III), and Fe(III). It was found that ordinary metal hydroxide precipitation was not feasible for obtaining a relatively pure product due to the co-precipitation of Al(III) and Fe(III). In this reported study, a basic zirconium sulfate precipitation method was investigated to recover Zr from a sulfuric acid leach solution of a eudialyte residue after rare earth elements extraction. Nb precipitated preferentially by adjusting the pH of the solution to around 1.0. After partial removal of SO42− by adding 120 g of CaCl2 per 1L solution, a basic zirconium sulfate precipitate was obtained by adjusting the pH to ~1.6 and maintaining the solution at 75 °C for 60 min. Under the optimum conditions, the loss of Zr during the SO42 removal step was only 0.11%, and the yield in the basic zirconium sulfate precipitation step was 96.18%. The precipitate contained 33.77% Zr and 0.59% Hf with low concentrations of Fe and Al. It was found that a high-quality product of ZrO2 could be obtained from the basic sulfate precipitate. Full article
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Article
Characterization of Magnetoelectropolished Stainless Steel Surfaces’ Texture by Using the Angle-Resolved Scattering and Image Processing Analysis Methods
Metals 2020, 10(8), 1098; https://doi.org/10.3390/met10081098 - 13 Aug 2020
Cited by 4 | Viewed by 924
Abstract
In this article, the results of preliminary experimental studies related to a fast, non-contact assessment of the AISI 316L stainless austenitic steel surfaces after electrochemical polishing in a magnetic field have been presented. The experiments were realized with the use of a modified [...] Read more.
In this article, the results of preliminary experimental studies related to a fast, non-contact assessment of the AISI 316L stainless austenitic steel surfaces after electrochemical polishing in a magnetic field have been presented. The experiments were realized with the use of a modified angle-resolved scattering (ARS) method based on the analysis of angular distribution of the scattered light intensity. Digital images of such distribution were acquired for selected areas of examined samples—base surface and surface after magnetoelectropolishing (MEP) process. Parametric analysis oriented toward the calculation of selected key geo- and photometric parameters carried out in Image Pro®-Plus software allowed for characterization of the surface conditions of the assessed samples in terms of their scattering properties. The obtained experimental results confirmed the usefulness of the ARS method used in the presented studies as well as the possibility of its practical use (after appropriate modifications) on a wider scale, especially in industrial applications. Full article
(This article belongs to the Special Issue Surface Engineering of Metals and Alloys)
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Review
Recent Advances in EBSD Characterization of Metals
Metals 2020, 10(8), 1097; https://doi.org/10.3390/met10081097 - 13 Aug 2020
Cited by 9 | Viewed by 2785
Abstract
Electron backscatter diffraction (EBSD) has been attracting enormous interest in the microstructural characterization of metals in recent years. This characterization technique has several advantages over conventional ones, since it allows obtaining a wide range of characterization possibilities in a single method, which is [...] Read more.
Electron backscatter diffraction (EBSD) has been attracting enormous interest in the microstructural characterization of metals in recent years. This characterization technique has several advantages over conventional ones, since it allows obtaining a wide range of characterization possibilities in a single method, which is not possible in others. The grain size, crystallographic orientation, texture, and grain boundary character distribution can be obtained by EBSD analysis. Despite the limited resolution of this technique (20–50 nm), EBSD is powerful, even for nanostructured materials. Through this technique, the microstructure can be characterized at different scales and levels with a high number of microstructural characteristics. It is known that the mechanical properties are strongly related to several microstructural aspects such as the size, shape, and distribution of grains, the presence of texture, grain boundaries character, and also the grain boundary plane distribution. In this context, this work aims to describe and discuss the possibilities of microstructural characterization, recent advances, the challenges in sample preparation, and the application of the EBSD in the characterization of metals. Full article
(This article belongs to the Special Issue Advances in Microstructural Characterization of Metals by EBSD)
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Article
Characterization of Coarse-Grained Heat-Affected Zones in Al and Ti-Deoxidized Offshore Steels
Metals 2020, 10(8), 1096; https://doi.org/10.3390/met10081096 - 13 Aug 2020
Cited by 2 | Viewed by 1403
Abstract
Deterioration of the toughness in heat-affected zones (HAZs) due to the thermal cycles caused by welding is a known problem in offshore steels. Acicular ferrite (AF) in the HAZ is generally considered beneficial regarding the toughness. Three experimental steels were studied in order [...] Read more.
Deterioration of the toughness in heat-affected zones (HAZs) due to the thermal cycles caused by welding is a known problem in offshore steels. Acicular ferrite (AF) in the HAZ is generally considered beneficial regarding the toughness. Three experimental steels were studied in order to find optimal conditions for the AF formation in the coarse-grained heat-affected zone (CGHAZ). One of the steels was Al-deoxidized, while the other two were Ti-deoxidized. The main focus was to distinguish whether the deoxidation practice affected the AF formation in the simulated CGHAZ. First, two different peak temperatures and prolonged annealing were used to study the prior austenite grain coarsening. Then, the effect of welding heat input was studied by applying three cooling times from 800 °C to 500 °C in a Gleeble thermomechanical simulator. The materials were characterized using electron microscopy, energy-dispersive X-ray spectrometry, and electron backscatter diffraction. The Mn depletion along the matrix-particle interface was modelled and measured. It was found that AF formed in the simulated CGHAZ of one of the Ti-deoxidized steels and its fraction increased with increasing cooling time. In this steel, the inclusions consisted mainly of small (1–4 μm) TiOx-MnS, and the tendency for prior austenite grain coarsening was the highest. Full article
(This article belongs to the Special Issue Inclusion/Precipitate Engineering in Steels)
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Article
The Oxidation Behaviors of Indefinite Chill Roll and High Speed Steel Materials
Metals 2020, 10(8), 1095; https://doi.org/10.3390/met10081095 - 13 Aug 2020
Cited by 1 | Viewed by 930
Abstract
Indefinite chill (IC) roll and high speed steel (HSS) materials have been widely employed to manufacture work rolls as latter and former stands in hot rolling mills. The oxidation of work rolls is of importance for the surface quality of the rolled workpieces. [...] Read more.
Indefinite chill (IC) roll and high speed steel (HSS) materials have been widely employed to manufacture work rolls as latter and former stands in hot rolling mills. The oxidation of work rolls is of importance for the surface quality of the rolled workpieces. The isothermal oxidation of the IC and HSS materials was conducted at 650 °C and 700 °C in both dry air and humid air. The isothermal oxidation curves indicate that HSS shows faster kinetics than the IC materials in dry air, whereas the opposite occurred in humid air. The oxide scales of the IC materials after the oxidation in both dry air and humid air are made up of two oxide phases. Two oxide phases were found when the HSS oxidized in the dry air and three oxide phases were found when oxidized in the humid air. Full article
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Article
A Constitutive Model for Yield Strength and Work Hardening Behaviour of Aluminium Alloys during Artificial Ageing
Metals 2020, 10(8), 1094; https://doi.org/10.3390/met10081094 - 13 Aug 2020
Cited by 3 | Viewed by 1027
Abstract
In this study, a unified constitutive model has been developed for both yield strength and work hardening behaviour prediction of aluminium alloys with different types of precipitates during and after artificial ageing. The different type and dimensions of general precipitate shapes (sphere, plate, [...] Read more.
In this study, a unified constitutive model has been developed for both yield strength and work hardening behaviour prediction of aluminium alloys with different types of precipitates during and after artificial ageing. The different type and dimensions of general precipitate shapes (sphere, plate, rod) have been classified and modelled by a primary dimension and aspect ratio, with which a general set of equations has been utilised to model the precipitates evolutions during ageing of various aluminium alloys. In addition, the effects of main microstructures on not only yield strength but also work-hardening behaviour of artificially aged aluminium alloys have been considered and modelled, based on which, a whole set of unified constitutive model considering both micro- and macro-properties for long-term artificial ageing of aluminium alloys has been proposed. Artificial ageing of two representative aluminium alloys (an Al-Mg-Si alloy AA6063 and an Al-Cu-Li alloy AA2198) has been adopted to show the capability and effectiveness of the developed model. The results show that the model can successfully predict the microstructures, yield strength and work hardening behaviour of various aluminium alloys with different precipitate types after long-term artificial ageing process, e.g., from 0 h to 500 h. It is believed that the model can be used for ageing of other aluminium alloys with dominant sphere, plate or rod-shaped precipitates. Full article
(This article belongs to the Special Issue Analysis and Design of Metal-Forming Processes)
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Article
Effect of Aging Treatment on Microstructure and Properties of the Fe55(CoCrNi)10(MoV)5C5 Medium-Entropy Alloy
Metals 2020, 10(8), 1093; https://doi.org/10.3390/met10081093 - 13 Aug 2020
Viewed by 983
Abstract
In this study; the effect of aging treatment for 4 h at 600–1000 °C on the microstructure and properties of a Fe55(CoCrNi)10(MoV)5C5 medium-entropy alloy (MEA) was investigated. After the alloy was aged at 800 °C, a [...] Read more.
In this study; the effect of aging treatment for 4 h at 600–1000 °C on the microstructure and properties of a Fe55(CoCrNi)10(MoV)5C5 medium-entropy alloy (MEA) was investigated. After the alloy was aged at 800 °C, a large number of granular and rod-shaped particles are formed throughout the face-centered cubic (FCC) matrix. The average particle diameter was measured to be approximately 46 nm, and the result of transmission electron microscopy (TEM) analysis verified that these secondary precipitates are VC carbides, which plays an important role for pinning dislocations and hindering dislocation movement. Therefore, the hardness and ultimate tensile strength of the alloy at this state increased from 253 HV, 322 MPa in cast condition to 326 HV, 626 MPa, respectively, while remaining relatively good elongation (6.2%). As the aging temperature increases, the volume fraction of the VC carbides decreased while its sizes increased; thus, the dispersion strengthening effect was reduced, resulting in the decrease in the hardness and strength. Full article
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Article
Fatigue Life Assessment of Revised Cope-Hole Details in Steel Truss Bridges
Metals 2020, 10(8), 1092; https://doi.org/10.3390/met10081092 - 12 Aug 2020
Cited by 1 | Viewed by 978
Abstract
In recent years, various welded details with complex local structure, ambiguous fatigue performance have appeared in fully welded steel truss bridges, however, they are not covered in the current design specifications. In order to study the fatigue performance of revised cope-hole details, fatigue [...] Read more.
In recent years, various welded details with complex local structure, ambiguous fatigue performance have appeared in fully welded steel truss bridges, however, they are not covered in the current design specifications. In order to study the fatigue performance of revised cope-hole details, fatigue performance experiments were designed and carried out on three specimens of revised detail with the same dimensions but subjected to different stress amplitude. Local finite element model of the revised cope-hole detail was established for further stress analysis. The results of finite element analysis were basically consistent with the static test results at majority of measurement points. Based on the existing fatigue test data and fatigue strength of cope-hole details defined in Eurocode and JSSC design code, the fatigue performance of revised cope-hole details was evaluated. The S-N fitting curve with the failure probability of 2.3% was obtained from the fatigue experiment results. The fatigue stress amplitude was 59.5 MPa when fatigue loading cycle was 2 × 106. It can be concluded that the fatigue performance of revised cope-hole detail was better than that of previous welded detail, which indicated that the revised detail had a significant improvement. Full article
(This article belongs to the Special Issue Fatigue Life Assessment under Random Loadings)
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Article
Effects of Inoculation on Structure Characteristics of High Silicon Ductile Cast Irons in Thin Wall Castings
Metals 2020, 10(8), 1091; https://doi.org/10.3390/met10081091 - 12 Aug 2020
Cited by 4 | Viewed by 1225
Abstract
Previous experiments pointed out that the deviation using a sphere as reference of graphite particles is noticeably increased by Si-alloying, with inoculation as a possible beneficial effect. The main objective of the present work is to evaluate the effects of commercial inoculants (Ca/Ca, [...] Read more.
Previous experiments pointed out that the deviation using a sphere as reference of graphite particles is noticeably increased by Si-alloying, with inoculation as a possible beneficial effect. The main objective of the present work is to evaluate the effects of commercial inoculants (Ca/Ca, Ba/Ca, RE-FeSi alloys) on 4.5%Si ductile iron, thin wall castings. FeSiMgRE treated iron (0.032–0.036%Mgres) is in-mold inoculated (a four-work-positions pattern). A complex chemical composition is obtained for each inoculation variant. Wedge casting W3 (ASTM A 367) is used to evaluate structure characteristics at different wall thickness (3–15 mm). Minimum and maximum size, area, nodule count, and representative graphite shape factors are evaluated. Roundness (including AG and Fmax) at 0.6–0.8 level illustrates the common formation of slightly irregular spheroidal graphite (Type V, ISO 945). Ca, RE-FeSi inoculation leads to the highest level of real perimeter and, consequently, to the lowest level of Sphericity. Ca, Ba-FeSi inoculation appears to be better than simple Ca-FeSi for improving graphite parameters, while Ca, RE-FeSi has the lowest beneficial effect, especially as it negatively affects the compactness degree of graphite particles. A two-step liquid treatment using RE-bearing FeSiCaMg master alloy and Ca, Ba-FeSi inoculant appears to be a solution to improve graphite parameters for high-Si ductile irons solidified in thin wall castings. Full article
(This article belongs to the Special Issue Thin Wall Iron Castings)
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Article
Application of Vacuum Techniques in Shell Moulds Produced by Additive Manufacturing
Metals 2020, 10(8), 1090; https://doi.org/10.3390/met10081090 - 12 Aug 2020
Cited by 2 | Viewed by 1088
Abstract
This research shows the feasibility of the additive manufacturing technique (AM), Binder Jetting (BJ), for the production of shell moulds, which are filled by vacuum suction in the field of aluminium parts production. In addition, this study compares the gravity pouring technique and [...] Read more.
This research shows the feasibility of the additive manufacturing technique (AM), Binder Jetting (BJ), for the production of shell moulds, which are filled by vacuum suction in the field of aluminium parts production. In addition, this study compares the gravity pouring technique and highlights the advantages of using vacuum techniques in AM moulds. A numerical simulation was carried out to study the behaviour of the liquid metal inside the moulds and the cooling rate of parts was analysed. The results show that in the gravity-pouring mould, the velocity in the gate causes moderate turbulence with small waves. However, vacuum suction keeps the velocity constant by eliminating waves and the filling process is homogeneous. Regarding dimensional accuracy, the staircase effect on the surface of the 3D moulds was the most critical aspect. The vacuum provides very homogeneous values of roughness across the entire surface of the part. Similarly, 3D scanning of castings revealed more accurate dimensions thanks to the help of vacuum forces. Finally, the microstructure of the cross section of the moulded parts shows that the porosity decreases with the vacuum filled. In both cases, the origin of the pores corresponds to gas entrapment and shrinkage during the filling process, the binder vaporization and nucleation points creation, leading to pores by shrinkage, gas entrapment or a mixture of both. This is the first study that uses vacuum filling techniques in moulds created by BJ, demonstrating the feasibility and advantages of AM using vacuum techniques, as an alternative to traditional casting. Full article
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Article
Low-Cycle Fatigue and Fracture Behavior of Aluminized Stainless Steel AISI 321 for Solar Thermal Power Generation Systems
Metals 2020, 10(8), 1089; https://doi.org/10.3390/met10081089 - 12 Aug 2020
Cited by 3 | Viewed by 1009
Abstract
The microstructure, low-cycle fatigue property, and fracture behavior of as-received and aluminized steel were investigated at room temperature, respectively. The results reveal that the aluminized layer is mainly composed of three layers: (I) the external Al2O3 layer, (II) the transition [...] Read more.
The microstructure, low-cycle fatigue property, and fracture behavior of as-received and aluminized steel were investigated at room temperature, respectively. The results reveal that the aluminized layer is mainly composed of three layers: (I) the external Al2O3 layer, (II) the transition Fe-Al mesophase layer, and (III) the diffusion layer with AlFe and AlCrFe phase. The microhardness of as-received steel lower than that of aluminized steel until the distance from aluminized layer is greater than 150 μm. Compared to the original steel, the aluminized steel exhibits lower stress amplitude and fatigue life, which is correlated to the surface integrity. According to the Coffin-Manson relationship, the fatigue-ductility coefficients for as-received and aluminized steel is 4.347 and 3.528, respectively. Fractographic analysis reveals that the fatigue cracks tend to nucleate at the coating and propagate through the grain boundaries apace. Full article
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Article
On the Intergranular Corrosion Properties of Thin Ferritic Stainless Steel Sheets Welded by Fiber-Laser
Metals 2020, 10(8), 1088; https://doi.org/10.3390/met10081088 - 12 Aug 2020
Cited by 6 | Viewed by 1088
Abstract
In the present investigation, thin sheets of stabilized and unstabilized ferritic stainless steel were welded in butt joint configuration using irradiation of a 1070 nm fiber-laser. Using optical microscopy, the microstructural evolution upon alternating heat input was characterized. In addition to that, [...] Read more.
In the present investigation, thin sheets of stabilized and unstabilized ferritic stainless steel were welded in butt joint configuration using irradiation of a 1070 nm fiber-laser. Using optical microscopy, the microstructural evolution upon alternating heat input was characterized. In addition to that, hardness and tensile tests were carried out on the specimens. Detailed focus was given to the intergranular corrosion properties, which were investigated on basis of the Strauss test with different times of exposure to the corrosive environment. Following these tests, the mechanical properties of the joints were characterized using tensile tests. A combination of the latter with an inspection by μ-CT analysis allows for the proposition of an intergranular corrosion rate with regard to the degradation of the joint strength. Full article
(This article belongs to the Special Issue Microstructure and Properties of Metallic Heat-Affected Zones)
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Article
Determination of Constitutive Equation and Thermo–Mechanical Processing Map for Pure Iridium
Metals 2020, 10(8), 1087; https://doi.org/10.3390/met10081087 - 12 Aug 2020
Cited by 1 | Viewed by 848
Abstract
Deformation behavior of pure iridium has been studied during thermal compression testing with the help of Gleeble-1500D in the temperature range of 1200 °C~1500 °C and strain rate range of 10−1 s−1~10−2 s−1. Resistance to deformation, microstructural [...] Read more.
Deformation behavior of pure iridium has been studied during thermal compression testing with the help of Gleeble-1500D in the temperature range of 1200 °C~1500 °C and strain rate range of 10−1 s−1~10−2 s−1. Resistance to deformation, microstructural evolution and hot workability of pure iridium have been used to analyze in detail. Frictional coefficient has been used to modify the experimental stress–strain curve of thermal compression test, and it has been found effective in reducing the influence of friction during thermo–mechanical testing. The hyperbolic sine constitutive equation of pure iridium has been established to give a material processing model for numerical simulation. A very high value of activation energy for iridium, 573 KJ/mol, clearly indicates that it is very hard to deform this material. The deformation mechanism of pure iridium is dependent upon temperature as well as strain rate. At low temperature and strain rate (temperature range of 1200 °C~1300 °C and strain rate range of 10−1 s−1~10−2 s−1), dynamic recovery is active while dynamic recrystallization becomes operative as temperature and stain rate are increased. On further increase in temperature and decrease in strain rate (temperature range of 1400 °C~1500 °C and strain rates of 10−2 s−1~10−3 s−1), abnormal grain growth takes place. On the basis of a constitutive model and processing map, suitable forming process parameters (temperature range of 1400 °C~1500 °C and strain rate range of 0.1 s−1~0.05 s−1) for pure iridium have been worked out. Full article
(This article belongs to the Special Issue Advances in Plastic Deformation Technologies)
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Article
Experimental Study on the Preparation of Cementing Materials by Direct Reduction Coupling of a Hematite-Carbon Base
Metals 2020, 10(8), 1086; https://doi.org/10.3390/met10081086 - 12 Aug 2020
Cited by 2 | Viewed by 771
Abstract
The reduction of iron in hematite and process coupling of cementing material generated from gangue components are explored in this paper, and a technical proposal for preparing directly reduced iron and cementing materials considering the processes of energy and material flows is proposed. [...] Read more.
The reduction of iron in hematite and process coupling of cementing material generated from gangue components are explored in this paper, and a technical proposal for preparing directly reduced iron and cementing materials considering the processes of energy and material flows is proposed. An experimental study preparing cementing materials, such as tricalcium silicate and dicalcium silicate, by roasting the components, was performed. In this study, hematite was used as the raw material and powdered carbon was added, as the reducing agent, with CaO; at the same time, the gangue components of iron ore were used as the principal raw materials for the process of directly reduced iron preparation by direct reduction of iron ore. The FactSage software package was used to perform thermodynamic calculations of the reduction of iron and its influence on the formation of tricalcium silicate and dicalcium silicate. The feasibility of the direct reduction of iron to elemental iron and preparation of cementing materials by roasting of gangue components under the studied thermodynamic conditions was discussed. Different temperature control strategies were used to verify the reaction coupling test. The results showed that zero-valent iron could be produced by roasting and reducing hematite under certain experimental conditions, and cementing materials, such as tricalcium silicate and dicalcium silicate, could be produced simultaneously by reacting the gangue components with CaO. Fe2O3 exerted an adverse effect on the formation of tricalcium silicate, and sufficient reduction of the iron was a precondition for the formation and stability of tricalcium silicate. Full article
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Article
Comparison of Precipitates and Texture Evolution in Nb-Bearing Grain-Oriented Silicon Steel Produced by Conventional Processing and Novel Twin-Roll Casting
Metals 2020, 10(8), 1085; https://doi.org/10.3390/met10081085 - 11 Aug 2020
Viewed by 889
Abstract
The Nb-bearing grain-oriented silicon steel sheets were produced by conventional route and novel twin-roll casting route, respectively. The microstructure, texture and precipitate evolution were comparatively investigated by using electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). The findings revealed that the precipitation [...] Read more.
The Nb-bearing grain-oriented silicon steel sheets were produced by conventional route and novel twin-roll casting route, respectively. The microstructure, texture and precipitate evolution were comparatively investigated by using electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). The findings revealed that the precipitation behavior and the texture evolution were totally different between the two processing routes. In the conventional route, a great number of nanoscale niobium nitride particles (NbN), which acted as mainly grain growth inhibitors were precipitated during hot rolling, while in the twin-roll casting route, due to the rapid solidification, the precipitation of NbN were suppressed and a new type Nb-bearing precipitate enriched with sulfur element was observed in the as-cast strip. Besides, the primary recrystallized texture of conventional specimens was characterized by strong γ-fiber with a peak at {111} <110>, together with very few Goss components. While in the case of twin-roll casting specimens, the strongest primary recrystallized texture was {111} <112> texture and the area fraction of Goss component was much higher than that of conventional specimens. After final high temperature annealing, complete secondary recrystallization was obtained in twin-roll casting specimens and the magnetic induction of B8 was 0.1 T higher than that of conventional specimens. Full article
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Article
Modeling of Fluid Flow and Residence-Time Distribution in a Five-Strand Tundish
Metals 2020, 10(8), 1084; https://doi.org/10.3390/met10081084 - 11 Aug 2020
Cited by 10 | Viewed by 1918
Abstract
Quantified residence-time distribution (RTD) provides a numerical characterization of mixing in the continuous casting tundish-thus allowing the engineer to better understand the metallurgical performance of the reactor. This study describes a computational fluid dynamic (CFD) modeling study for analyzing the flow pattern and [...] Read more.
Quantified residence-time distribution (RTD) provides a numerical characterization of mixing in the continuous casting tundish-thus allowing the engineer to better understand the metallurgical performance of the reactor. This study describes a computational fluid dynamic (CFD) modeling study for analyzing the flow pattern and the residence-time distribution in a five-strand tundish. Two passive scalar-transport equations were applied to separately calculate the E-curve and F-curve in the tundish. The numeric modeling result were compared to water-modeling results to validate the mathematical model. The volume fraction of different flow regions (plug, mixed and dead) and the intermixing time during the ladle changeover were calculated to study the effects of the flow control device (FCD) on the tundish performance. From the results of CFD calculations, it can be stated that a combination of the U-baffle with deflector holes and the turbulence inhibitor had three major effects on the flow characteristics in the tundish: (i) to reduce the extent of the dead volume; (ii) to evenly distribute the liquid streams to each strand and (iii) to shorten the intermixing time during the ladle changeover operation. Full article
(This article belongs to the Special Issue Numerical Modelling in Steel Metallurgy)
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Article
Optimization of Microwave Reductive Roasting Process of Bauxite Residue
Metals 2020, 10(8), 1083; https://doi.org/10.3390/met10081083 - 11 Aug 2020
Cited by 2 | Viewed by 1134
Abstract
In this study, microwave-assisted heating is presented as a suitable method to transform the hematite and goethite contained in bauxite residue into magnetite, wüstite, and metallic iron, with a short processing time. The final target was the production of a sinter with strong [...] Read more.
In this study, microwave-assisted heating is presented as a suitable method to transform the hematite and goethite contained in bauxite residue into magnetite, wüstite, and metallic iron, with a short processing time. The final target was the production of a sinter with strong magnetic properties, allowing the magnetic separation of Fe from the residue. The influence of microwave energy on the sample, the effect of irradiation time, and the carbon/bauxite residue mass ratio (C/BR) were the parameters that have been analyzed to optimize the process. Their optimized combination allowed transforming 79% of the iron present in the sinter into metallic iron. However, hercynite was also formed, and the presence of this mineralogical phase could be considered a possible drawback for its magnetic properties. Full article
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Article
Intergranular to Intragranular Pitting Corrosion Transition Mechanism of Sensitized AA5083 at 150 °C
Metals 2020, 10(8), 1082; https://doi.org/10.3390/met10081082 - 11 Aug 2020
Cited by 3 | Viewed by 1152
Abstract
Intergranular corrosion (IGC) and pitting transition caused by grain boundary β-phase saturation of aluminum alloy AA5083 sensitized at 150 °C was investigated in 3.5 wt% NaCl solution. The change in the localized corrosion mechanism from IGC to pitting was studied by microstructural and [...] Read more.
Intergranular corrosion (IGC) and pitting transition caused by grain boundary β-phase saturation of aluminum alloy AA5083 sensitized at 150 °C was investigated in 3.5 wt% NaCl solution. The change in the localized corrosion mechanism from IGC to pitting was studied by microstructural and electrochemical analysis, where IGC was found to be the primary mechanism at low degrees of sensitization (DoS) and pitting corrosion was observed to develop after grain boundary β-phase saturation. Evaluation of the double layer capacitance by electrochemical impedance spectroscopy (EIS) and charge passed through the specimens by potentiostatic current monitoring demonstrated a well differentiated three-stage dissolution mechanism. Full article
(This article belongs to the Special Issue Corrosion and Inhibition Processes)
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Article
Influence of Surface Ultrasonic Rolling on Microstructure and Corrosion Property of T4003 Ferritic Stainless Steel Welded Joint
Metals 2020, 10(8), 1081; https://doi.org/10.3390/met10081081 - 11 Aug 2020
Cited by 3 | Viewed by 925
Abstract
In this paper, the effect of surface ultrasonic rolling treatment (SURT) on surface properties of T4003 cold metal transfer (CMT) welded joints was studied. Surface topography and microstructure changes of the welded joint surface before and after SURT were observed by optical microscope [...] Read more.
In this paper, the effect of surface ultrasonic rolling treatment (SURT) on surface properties of T4003 cold metal transfer (CMT) welded joints was studied. Surface topography and microstructure changes of the welded joint surface before and after SURT were observed by optical microscope and scanning electron microscope. The hardness and residual stress distribution of welded joint were measured by a microhardness tester and X-ray diffractometer. The change of corrosion resistance of welded joints was studied by electrochemical polarization curve measurement. The results show that surface roughness (Ra) of the weld zone, heat affect zone (HAZ), and base metal after SURT was reduced to 0.320 μm, 0.156 μm, and 0.227 μm, respectively, and surface morphology became smooth. The plastic deformation layer and working hardening layer were formed at the welded joint. The degree of plastic deformation of the weld zone was more serious than that in the base metal, and grains in weld zone was obviously refined. The thickness of plastic deformation layer was about 100 μm. The surface hardness in the weld zone was highest, which is about 420 HV. The refinement of grains and the increase of surface hardness can improve the fatigue life of welded joint. After SURT, the residual stress in the welded joint changes from residual tensile stress to residual compressive stress, which can also improve fatigue life of the welded joint. Surface corrosion resistance of welded joints after SURT was improved due to smooth surface and the formation of fine grains layer. Full article
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Review
Spark Plasma Sintering of Titanium Aluminides: A Progress Review on Processing, Structure-Property Relations, Alloy Development and Challenges
Metals 2020, 10(8), 1080; https://doi.org/10.3390/met10081080 - 11 Aug 2020
Cited by 10 | Viewed by 1758
Abstract
Titanium aluminides (TiAl) have the potential of substituting nickel-based superalloys (NBSAs) in the aerospace industries owing to their lightweight, good mechanical and oxidation properties. Functional simplicity, control of sintering parameters, exceptional sintering speeds, high reproducibility, consistency and safety are the main benefits of [...] Read more.
Titanium aluminides (TiAl) have the potential of substituting nickel-based superalloys (NBSAs) in the aerospace industries owing to their lightweight, good mechanical and oxidation properties. Functional simplicity, control of sintering parameters, exceptional sintering speeds, high reproducibility, consistency and safety are the main benefits of spark plasma sintering (SPS) over conventional methods. Though TiAl exhibit excellent high temperature properties, SPS has been employed to improve on the poor ductility at room temperature. Powder metallurgical processing techniques used to promote the formation of refined, homogeneous and contaminant-free structures, favouring improvements in ductility and other properties are discussed. This article further reviews published work on phase constituents, microstructures, alloy developments and mechanical properties of TiAl alloys produced by SPS. Finally, an overview of challenges in as far as the implementation of TiAl in industries of interest are highlighted. Full article
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