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Crystals
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Development of High Entropy Alloys
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Development of High Entropy Alloys

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (31 May 2020) | Viewed by 28098

Special Issue Editor

Dr. Bharat Gwalani

E-Mail Website
Guest Editor
Pacific Northwest National Laboratory, Richland, USA
Interests: high-entropy alloys; atom probe tomography; additive manufacturing; shear-assisted alloying; high strain rate deforamtion
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

High-entropy alloys offer an ability to engineer unique microstructures achieved by manipulating their compositional complexity. Often, the experimentally-observed, single-phase high-entropy alloy (HEA) is the result of second-phase precipitation constrained by thermodynamic and/or kinetic factors. Several metastable phases, which are not predicted by equilibrium phase diagrams, are also often reported to be present in HEAs. Further, a large microstructural variation is noted in these alloys when processed using different processing routes, due to abundant mutually exclusive phase transformation pathways. These dramatically different phase transformation pathways can lead to some rather exceptional mechanical properties that can also vary over a large range. In addition, several reports have suggested that the deformation mechanisms of HEAs can be fundamentally different compared to solute lean alloys. With the rapidly growing interest in HEAs, this symposium aims to bring the worldwide HEA research community together to present and discuss the latest results on microstructural engineering and resultant unique properties that can be achieved using HEAs.

The areas of interest for this Special Issue are novel microstructures in HEAs, unconventional strengthening phases, the metastability engineering of phases, multiple strengthening mechanisms due to the hierarchical effect of microstructures, and other novel topics within HEAs. Both experimental and computational works on these topics are welcome.

Dr. Bharat Gwalani
Guest Editor

Manuscript Submission Information

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Keywords

  • Characterization
  • Mechanical properties
  • Deformation
  • Dislocations
  • Transformation pathways
  • Metastability

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Published Papers (6 papers)

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Research

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15 pages, 19460 KiB  
Article
Laser Metal Deposition of an AlCoCrFeNiTi0.5 High-Entropy Alloy Coating on a Ti6Al4V Substrate: Microstructure and Oxidation Behavior
by Wenyuan Cui, Wei Li, Wei-Ting Chen and Frank Liou
Crystals 2020, 10(8), 638; https://doi.org/10.3390/cryst10080638 - 23 Jul 2020
Cited by 30 | Viewed by 4389
Abstract
Ti6Al4V has been recognized as an attractive material, due to its combination of low density and favorable mechanical properties. However, its insufficient oxidation resistance has limited the high-temperature application. In this work, an AlCoCrFeNiTi0.5 high-entropy alloy (HEA) coating was fabricated on a [...] Read more.
Ti6Al4V has been recognized as an attractive material, due to its combination of low density and favorable mechanical properties. However, its insufficient oxidation resistance has limited the high-temperature application. In this work, an AlCoCrFeNiTi0.5 high-entropy alloy (HEA) coating was fabricated on a Ti6Al4V substrate using laser metal deposition (LMD). The microstructure and isothermal oxidation behaviors were investigated. The microstructure of as-deposited HEA exhibited a Fe, Cr-rich A2 phase and an Al, Ni, Ti-enriched B2 phase. Its hardness was approximately 2.1 times higher than that of the substrate. The oxidation testing at 700 °C and 800 °C suggested that the HEA coating has better oxidation resistance than the Ti6Al4V substrate. The oxide scales of the Ti6Al4V substrate were mainly composed of TiO2, while continuous Al2O3 and Cr2O3 were formed in the HEA coatings and could be attributed to oxidation resistance improvement. This work provides an approach to mitigate the oxidation resistance of Ti6Al4V and explore the applicability of the HEA in a high-temperature environment. Full article
(This article belongs to the Special Issue Development of High Entropy Alloys)
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20 pages, 15613 KiB  
Article
Liquid Phase Separation in Ag-Co-Cr-Fe-Mn-Ni, Co Cr-Cu-Fe-Mn-Ni and Co-Cr-Cu-Fe-Mn-Ni-B High Entropy Alloys for Biomedical Application
by Takeshi Nagase, Mitsuharu Todai and Takayoshi Nakano
Crystals 2020, 10(6), 527; https://doi.org/10.3390/cryst10060527 - 20 Jun 2020
Cited by 16 | Viewed by 5347
Abstract
The liquid phase separation (LPS) behavior in Co-Cr-based high-entropy alloys (HEAs) is an important target for the development of Co-Cr-based HEAs for metallic biomaterials (BioHEAs). The solidification microstructure in Ag-Co-Cr-Fe-Mn-Ni-Ag, Co-Cr-Cu-Fe-Mn-Ni-Cu, and Co-Cr-Cu-Fe-Mn-Ni-B HEAs, which were designed as the combination of the equiatomic [...] Read more.
The liquid phase separation (LPS) behavior in Co-Cr-based high-entropy alloys (HEAs) is an important target for the development of Co-Cr-based HEAs for metallic biomaterials (BioHEAs). The solidification microstructure in Ag-Co-Cr-Fe-Mn-Ni-Ag, Co-Cr-Cu-Fe-Mn-Ni-Cu, and Co-Cr-Cu-Fe-Mn-Ni-B HEAs, which were designed as the combination of the equiatomic CoCrFeMnNi with Ag, Cu, and the interstitial element of B, was investigated as the fundamental research of LPS in Co-Cr-based HEAs. Ingots of equiatomic AgCoCrFeMnNi, equiatomic CoCrCuFeMnNi, non-equiatomic CoCrCuxFeMnNi (x = 2, 3), and CoCrCuxFeMnNiB0.2 (x = 1, 2, 3) with a small amount of B were fabricated using the arc-melting process. A macroscopic phase-separated structure was observed in the ingots of the equiatomic AgCoCrFeMnNi and CoCrCuxFeMnNiB0.2 (x = 2, 3) HEAs. The addition of a small amount of B enhanced the LPS tendency in the Co-Cr-Fe-Mn-Ni-Cu HEAs. The LPS behavior was discussed through the heat of mixing and computer coupling of phase diagrams and thermochemistry (CALPHAD). Full article
(This article belongs to the Special Issue Development of High Entropy Alloys)
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14 pages, 2798 KiB  
Article
Microstructures and Wear Resistance of CoCrFeNi2V0.5Tix High-Entropy Alloy Coatings Prepared by Laser Cladding
by Yaning Li, Hui Liang, Qiuxin Nie, Zhaoxin Qi, Dewei Deng, Hui Jiang and Zhiqiang Cao
Crystals 2020, 10(5), 352; https://doi.org/10.3390/cryst10050352 - 29 Apr 2020
Cited by 38 | Viewed by 3473
Abstract
CoCrFeNi2V0.5Tix high entropy alloy coatings were synthesized by laser cladding on Ti-6Al-4V (annotated as TC4) substrate. The microstructures, hardness, and wear properties of the coatings were studied in detail. The results showed that these coatings were all composed [...] Read more.
CoCrFeNi2V0.5Tix high entropy alloy coatings were synthesized by laser cladding on Ti-6Al-4V (annotated as TC4) substrate. The microstructures, hardness, and wear properties of the coatings were studied in detail. The results showed that these coatings were all composed of body-centered cubic (BCC) solid solution, (Co,Ni)Ti2 phase, and Ti-rich phase. With the increase of Ti content (x in the range of 0–1.0), the hardness of these coatings (about 960 HV) was basically unchanged and stabilized, whereas, when x was increased to 1.25, the correspondent hardness was decreased significantly to about 830 HV. Compared with original substrate, the wear resistance of high-entropy alloy (HEA) coatings was greatly improved. In particular, CoCrFeNi2V0.5Ti0.75 (donated as Ti0.75) exhibited the lowest wear rate, width, and depth of tracks of wear, indicating the best wear resistance. Moreover, the wear mechanisms of Ti0.75 coating were mainly adhesive wear and oxidative wear. Full article
(This article belongs to the Special Issue Development of High Entropy Alloys)
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11 pages, 3544 KiB  
Article
Laser Cladding of Al0.5CoCrCuFeNiSi High Entropy Alloy Coating without and with Yttria Addition on H13 Steel
by Jingda Liu, Yuxin Guan, Xuechen Xia, Pai Peng, Qifeng Ding and Xiaotao Liu
Crystals 2020, 10(4), 320; https://doi.org/10.3390/cryst10040320 - 20 Apr 2020
Cited by 12 | Viewed by 3127
Abstract
Al0.5CoCrCuFeNiSi high entropy alloy coating without and with a 1 wt.% Y2O3 addition was fabricated by laser cladding technique on H13 substrate. The results showed that the laser cladding coatings without and with Y2O3 addition [...] Read more.
Al0.5CoCrCuFeNiSi high entropy alloy coating without and with a 1 wt.% Y2O3 addition was fabricated by laser cladding technique on H13 substrate. The results showed that the laser cladding coatings without and with Y2O3 addition consist of a mixture of body centered cubic (BCC) dendrites and face centered cubic (FCC) interdendrites. With the addition of Y2O3, the peaks of BCC dendrites in the coating shifted to leftwards, which is caused by the distortion of lattice due to the dissolution of Y with larger atomic radius. There exist cracks and porosities in the coating without Y2O3 addition. With Y2O3 addition, the cracks and porosities in the laser cladding coating were inhibited greatly. In addition, the microstructure of the coating with Y2O3 addition was refined due to the improving of the ratio of nucleation. The enhancement of properties, such as hardness, wear resistance and corrosion resistance, of the coating with Y2O3 addition came from the inhibition of cracks and porosities and the refinement of microstructure. Full article
(This article belongs to the Special Issue Development of High Entropy Alloys)
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10 pages, 2037 KiB  
Article
Wear and Corrosion Behaviour of Supersaturated Surface Layers in the High-Entropy Alloy Systems CrMnFeCoNi and CrFeCoNi
by Thomas Lindner, Martin Löbel, Erik Saborowski, Lisa-Marie Rymer and Thomas Lampke
Crystals 2020, 10(2), 110; https://doi.org/10.3390/cryst10020110 - 12 Feb 2020
Cited by 21 | Viewed by 3349
Abstract
The surface hardening of single-face-centred cubic (fcc)-phase CrMnFeCoNi and the manganese-free CrFeCoNi alloy was conducted using low-temperature nitrocarburisation. The microstructural investigations reveal the successful formation of a homogeneous diffusion layer with a thickness of approximately 16 µm. The interstitial solution of carbon and [...] Read more.
The surface hardening of single-face-centred cubic (fcc)-phase CrMnFeCoNi and the manganese-free CrFeCoNi alloy was conducted using low-temperature nitrocarburisation. The microstructural investigations reveal the successful formation of a homogeneous diffusion layer with a thickness of approximately 16 µm. The interstitial solution of carbon and nitrogen causes an anisotropic lattice expansion. The increase in microhardness is in accordance to the graded concentration profile of the interstitial elements. Wear tests show a significantly enhanced resistance at different loads. The electrochemical tests reveal no deterioration in the corrosion resistance. The absence of precipitates is proven by microstructural investigations. The results prove the applicability of the concept of solution hardening by the formation of supersaturated solutions for the material group of high-entropy alloys. Hence, an increase of entropy with the consideration of lattice interstices provides new development approaches. Full article
(This article belongs to the Special Issue Development of High Entropy Alloys)
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Review

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18 pages, 2887 KiB  
Review
Mechanical and Magnetic Properties of the High-Entropy Alloys for Combinatorial Approaches
by E-Wen Huang, Guo-Yu Hung, Soo Yeol Lee, Jayant Jain, Kuan-Pang Chang, Jing Jhe Chou, Wen-Chi Yang and Peter K. Liaw
Crystals 2020, 10(3), 200; https://doi.org/10.3390/cryst10030200 - 14 Mar 2020
Cited by 31 | Viewed by 7512
Abstract
This review summarizes the state of high-entropy alloys and their combinatorial approaches, mainly considering their magnetic applications. Several earlier studies on high-entropy alloy properties, such as magnetic, wear, and corrosion behavior; different forms, such as thin films, nanowires, thermal spray coatings; specific treatments, [...] Read more.
This review summarizes the state of high-entropy alloys and their combinatorial approaches, mainly considering their magnetic applications. Several earlier studies on high-entropy alloy properties, such as magnetic, wear, and corrosion behavior; different forms, such as thin films, nanowires, thermal spray coatings; specific treatments, such as plasma spraying and inclusion effects; and unique applications, such as welding, are summarized. High-entropy alloy systems that were reported for both their mechanical and magnetic properties are compared through the combination of their Young’s modulus, yield strength, remanent induction, and coercive force. Several potential applications requiring both mechanical and magnetic properties are reported. Full article
(This article belongs to the Special Issue Development of High Entropy Alloys)
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