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Metals, Volume 7, Issue 1 (January 2017)

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Cover Story (view full-size image) The coating of hollow alumino-silicate microspheres or cenospheres with thin layers of Cu by means [...] Read more.
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Open AccessFeature PaperTechnical Note Tensile Ductility of Nanostructured Bainitic Steels: Influence of Retained Austenite Stability
Metals 2017, 7(1), 31; https://doi.org/10.3390/met7010031
Received: 19 December 2016 / Revised: 9 January 2017 / Accepted: 16 January 2017 / Published: 23 January 2017
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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
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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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Open AccessArticle Electropolishing Behaviour of 73 Brass in a 70 vol % H3PO4 Solution by Using a Rotating Cylinder Electrode (RCE)
Metals 2017, 7(1), 30; https://doi.org/10.3390/met7010030
Received: 19 August 2016 / Revised: 16 December 2016 / Accepted: 16 January 2017 / Published: 20 January 2017
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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,
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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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Open AccessArticle Effect of Annealing Temperature on the Corrosion Protection of Hot Swaged Ti-54M Alloy in 2 M HCl Pickling Solutions
Metals 2017, 7(1), 29; https://doi.org/10.3390/met7010029
Received: 13 November 2016 / Revised: 20 December 2016 / Accepted: 11 January 2017 / Published: 20 January 2017
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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
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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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Open AccessArticle Study on the Tribological Properties of Porous Titanium Sliding against Tungsten Carbide YG6
Metals 2017, 7(1), 28; https://doi.org/10.3390/met7010028
Received: 6 September 2016 / Revised: 2 January 2017 / Accepted: 11 January 2017 / Published: 20 January 2017
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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
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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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Open AccessArticle Effects of Austenitizing Conditions on the Microstructure of AISI M42 High-Speed Steel
Metals 2017, 7(1), 27; https://doi.org/10.3390/met7010027
Received: 4 December 2016 / Revised: 3 January 2017 / Accepted: 12 January 2017 / Published: 18 January 2017
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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 Ms and Mf 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) Printed Edition available
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Open AccessArticle The Influence of Austenite Grain Size on the Mechanical Properties of Low-Alloy Steel with Boron
Metals 2017, 7(1), 26; https://doi.org/10.3390/met7010026
Received: 21 November 2016 / Revised: 10 January 2017 / Accepted: 12 January 2017 / Published: 17 January 2017
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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
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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) Printed Edition available
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Open AccessArticle Effect of Heavy Ion Irradiation Dosage on the Hardness of SA508-IV Reactor Pressure Vessel Steel
Metals 2017, 7(1), 25; https://doi.org/10.3390/met7010025
Received: 6 November 2016 / Revised: 21 December 2016 / Accepted: 10 January 2017 / Published: 14 January 2017
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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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Open AccessArticle One-Dimensional Constitutive Model for Porous Titanium Alloy at Various Strain Rates and Temperatures
Metals 2017, 7(1), 24; https://doi.org/10.3390/met7010024
Received: 11 November 2016 / Revised: 19 December 2016 / Accepted: 26 December 2016 / Published: 12 January 2017
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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
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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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Open AccessArticle Effect of Controlled Cooling on Microstructure and Tensile Properties of Low C Nb-Ti-Containing HSLA Steel for Construction
Metals 2017, 7(1), 23; https://doi.org/10.3390/met7010023
Received: 16 November 2016 / Revised: 20 December 2016 / Accepted: 4 January 2017 / Published: 12 January 2017
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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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Open AccessArticle The Effect of Diffusion Welding Parameters on the Mechanical Properties of Titanium Alloy and Aluminum Couples
Metals 2017, 7(1), 22; https://doi.org/10.3390/met7010022
Received: 28 October 2016 / Revised: 4 January 2017 / Accepted: 5 January 2017 / Published: 11 January 2017
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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
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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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Open AccessArticle Study of Adsorption of Hydrogen on Al, Cu, Mg, Ti Surfaces in Al Alloy Melt via First Principles Calculation
Metals 2017, 7(1), 21; https://doi.org/10.3390/met7010021
Received: 4 November 2016 / Revised: 3 December 2016 / Accepted: 13 December 2016 / Published: 11 January 2017
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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
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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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Open AccessEditorial Acknowledgement to Reviewers of Metals in 2016
Metals 2017, 7(1), 20; https://doi.org/10.3390/met7010020
Received: 11 January 2017 / Revised: 11 January 2017 / Accepted: 11 January 2017 / Published: 11 January 2017
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Abstract
The editors of Metals would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2016.[...] Full article
Open AccessArticle Properties of Resistance Spot-Welded TWIP Steels
Metals 2017, 7(1), 14; https://doi.org/10.3390/met7010014
Received: 31 October 2016 / Revised: 15 December 2016 / Accepted: 16 December 2016 / Published: 11 January 2017
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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
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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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Open AccessArticle Optimization of Copper Removal from Aqueous Solutions Using Emulsion Liquid Membranes with Benzoylacetone as a Carrier
Metals 2017, 7(1), 19; https://doi.org/10.3390/met7010019
Received: 5 December 2016 / Revised: 20 December 2016 / Accepted: 4 January 2017 / Published: 10 January 2017
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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
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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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Open AccessFeature PaperArticle The Al Effects of Co-Free and V-Containing High-Entropy Alloys
Metals 2017, 7(1), 18; https://doi.org/10.3390/met7010018
Received: 19 December 2016 / Revised: 27 December 2016 / Accepted: 5 January 2017 / Published: 10 January 2017
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Abstract
In this study, five-component high-entropy alloys (HEAs) AlxCrFeNiV (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
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In this study, five-component high-entropy alloys (HEAs) AlxCrFeNiV (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, AlxCrFeNiV (x = 0.3, and 0.5), were systematically studied through the use of various characterization methods in the as-cast state. The Al0.3CrFeNiV 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 Al0.5CrFeNiV 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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