Editorial

2 pages, 165 KiB

Open AccessEditorial

High Entropy Materials: Challenges and Prospects

by Peter K. Liaw and Weidong Li

Metals 2021, 11(10), 1643; https://doi.org/10.3390/met11101643 - 15 Oct 2021

Cited by 9 | Viewed by 2030

Entropy is an important concept in thermodynamics, measuring the disorder in a system or, more precisely, the number of possible microscopic configurations of individual atoms or molecules of a system, i.e., microstates [...] Full article

(This article belongs to the Special Issue High Entropy Materials: Challenges and Prospects)

Research

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12 pages, 5478 KiB

Open AccessArticle

Production and Properties of High Entropy Carbide Based Hardmetals

by Johannes Pötschke, Manisha Dahal, Anne Vornberger, Mathias Herrmann and Alexander Michaelis

Metals 2021, 11(2), 271; https://doi.org/10.3390/met11020271 - 05 Feb 2021

Cited by 24 | Viewed by 3101

Abstract

Dense, high-entropy carbide cobalt-bonded hardmetals with two different compositions, namely (Hf-Ta-Ti-Nb-V)C-19.2 vol% Co and (Ta-Ti-Nb-V-W)C-19.2 vol% Co, were successfully manufactured by gas pressure sintering (SinterHIP) at 1400 °C and 100 bar Ar pressure. The microstructure of these hardmetals consists of a rigid skeletal [...] Read more.

Dense, high-entropy carbide cobalt-bonded hardmetals with two different compositions, namely (Hf-Ta-Ti-Nb-V)C-19.2 vol% Co and (Ta-Ti-Nb-V-W)C-19.2 vol% Co, were successfully manufactured by gas pressure sintering (SinterHIP) at 1400 °C and 100 bar Ar pressure. The microstructure of these hardmetals consists of a rigid skeletal carbide phase embedded in a tough Co binder phase. EDS mappings showed that the high-entropy carbide phase did not decompose and that a typical hardmetal microstructure was realized. Only in the case of the (Hf-Ta-Ti-Nb-V)C-Co hardmetal was some undissolved TaC and HfO₂, as well as some clustered vanadium titanium carbide phase, found, resulting in a split-up of the HEC phase into two very similar HEC phases. This resulted in a reduced hardness to fracture toughness ratio for this composition. Measurements of magnetic saturation polarization showed values between 57.5% and 70% of theoretical magnetic saturation polarization, indicating marginal dissolution of the carbide-forming metal elements in the binder phase. The hardness value HV10 for (Hf-Ta-Ti-Nb-V)C-19.2 vol% Co was 1203 HV10 and 1432 HV10 for (Ta-Ti-Nb-V-W)C-19.2 vol% Co. Full article

(This article belongs to the Special Issue High Entropy Materials: Challenges and Prospects)

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8 pages, 2163 KiB

Open AccessArticle

Fatigue Behavior of Zr₅₈Cu_15.46Ni_12.74Al_10.34Nb_2.76Y_0.5 Bulk Metallic Glass Fabricated by Industrial-Grade Zirconium Raw Material

by Shichao Zhou, Tao Zhang, Lugee Li, Jiedan Yang, Min Zhang, Chengyong Wang and Yong Zhang

Metals 2021, 11(2), 187; https://doi.org/10.3390/met11020187 - 21 Jan 2021

Cited by 4 | Viewed by 1714

Abstract

In this work, the fatigue behavior of a low-cost Zr₅₈Cu_15.46Ni_12.74Al_10.34Nb_2.76Y_0.5 (at%) bulk metallic glass (BMG) fabricated by industrial-grade Zirconium raw material was investigated under three-point bending loading mode. X-ray, fatigue tests under [...] Read more.

In this work, the fatigue behavior of a low-cost Zr₅₈Cu_15.46Ni_12.74Al_10.34Nb_2.76Y_0.5 (at%) bulk metallic glass (BMG) fabricated by industrial-grade Zirconium raw material was investigated under three-point bending loading mode. X-ray, fatigue tests under different stress amplitude and fatigue fractography were conducted in order to characterize the amorphous structure, fatigue stress-life (S-N) curve and fracture mechanism, respectively. It is found that the X-ray diffraction (XRD) result showed a fully amorphous structure due to high glass-forming ability, cracks initiated from inclusions near the rectangular corners at tensile surfaces and the fatigue endurance limit (~168 MPa) and fatigue ratio (~0.13) termed as fatigue endurance limit divided by ultimate tensile strength in stress amplitude were comparable to the similar BMG prepared by high pure raw materials. Full article

(This article belongs to the Special Issue High Entropy Materials: Challenges and Prospects)

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13 pages, 4126 KiB

Open AccessArticle

Microstructure Evolution and Mechanical Properties of Refractory Mo-Nb-V-W-Ti High-Entropy Alloys

by Maximilian Regenberg, Georg Hasemann, Markus Wilke, Thorsten Halle and Manja Krüger

Metals 2020, 10(11), 1530; https://doi.org/10.3390/met10111530 - 18 Nov 2020

Cited by 13 | Viewed by 2709

Abstract

High-entropy alloys can either be defined as solid solution alloys containing at least five elements in equiatomic or near-equiatomic composition, or as alloys with high configurational entropies (larger than 1.5R), regardless of the number of elements involved. The present study reports on an [...] Read more.

High-entropy alloys can either be defined as solid solution alloys containing at least five elements in equiatomic or near-equiatomic composition, or as alloys with high configurational entropies (larger than 1.5R), regardless of the number of elements involved. The present study reports on an alloy design route for refractory high-entropy alloys based on equiatomic Mo-Nb-V alloys with additions of W and Ti. In general, the work was motivated by Senkov et al. The aim of the experiments carried out was to produce a refractory high-entropy alloy with a single-phase structure. For this purpose, a systematic alloy design involving four- and five-element compositions was used. Scanning electron microscopy analysis has shown that Mo-Nb-V-xW-yTi (x = 0, 20; y = 5, 10, 15, 20, 25) is in fact a refractory high-entropy alloy with a body-centered cubic dendritic structure. Furthermore, the Ti-concentration of the experimental alloys was varied, to obtain the influence of Titanium on the microstructure development. Additionally, compressive tests at room temperature were carried out to evaluate the influence of the different alloying elements and the Ti-fraction on the mechanical properties. The observations of the present work are then compared to the published results on similar alloys from the working group of Yao et al. and critically discussed. Full article

(This article belongs to the Special Issue High Entropy Materials: Challenges and Prospects)

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14 pages, 5666 KiB

Open AccessArticle

Microstructures and Tribological Properties of TiC Reinforced FeCoNiCuAl High-Entropy Alloy at Normal and Elevated Temperature

by Tie Zhu, Hong Wu, Rui Zhou, Ningyi Zhang, Yong Yin, Luxin Liang, Yong Liu, Jia Li, Quan Shan, Qingxiang Li and Weidong Huang

Metals 2020, 10(3), 387; https://doi.org/10.3390/met10030387 - 18 Mar 2020

Cited by 31 | Viewed by 2975

Abstract

Recent studies have suggested that high-entropy alloys (HEAs) possess high fracture toughness, good wear resistance, and excellent high-temperature mechanical properties. In order to further improve their properties, a batch of TiC-reinforced FeCoNiCuAl HEA composites were fabricated by mechanical alloying and spark plasma sintering. [...] Read more.

Recent studies have suggested that high-entropy alloys (HEAs) possess high fracture toughness, good wear resistance, and excellent high-temperature mechanical properties. In order to further improve their properties, a batch of TiC-reinforced FeCoNiCuAl HEA composites were fabricated by mechanical alloying and spark plasma sintering. X-ray diffractometry analysis of the TiC-reinforced HEA composites, combined with scanning electron microscopy imaging, indicated that TiC particles were uniformly distributed in the face-centered cubic and body-centered cubic phases. The room temperature hardness of the FeCoNiCuAl HEA was increased from 467 to 768 HV with the addition of TiC, owing to precipitation strengthening and fine grain strengthening effects. As the TiC content increased, the friction coefficient of the FeCoNiCuAl HEA first increased and then decreased at room temperature, due to the transition of the wear mechanism from adhesive to abrasive behavior. At higher temperature, the friction coefficient of the FeCoNiCuAl HEA monotonously reduced, corresponding well with the transition from adhesive wear to oxidative wear. Full article

(This article belongs to the Special Issue High Entropy Materials: Challenges and Prospects)

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15 pages, 7100 KiB

Open AccessArticle

Laser Beam Welding of a Low Density Refractory High Entropy Alloy

by Evgeniya Panina, Nikita Yurchenko, Sergey Zherebtsov, Nikita Stepanov, Gennady Salishchev, Volker Ventzke, René Dinse and Nikolai Kashaev

Metals 2019, 9(12), 1351; https://doi.org/10.3390/met9121351 - 16 Dec 2019

Cited by 20 | Viewed by 3584

Abstract

The effect of laser beam welding on the structure and properties of a Ti_1.89NbCrV_0.56 refractory high entropy alloy was studied. In particular, the effect of different pre-heating temperatures was examined. Due to the low ductility of the material, laser beam [...] Read more.

The effect of laser beam welding on the structure and properties of a Ti_1.89NbCrV_0.56 refractory high entropy alloy was studied. In particular, the effect of different pre-heating temperatures was examined. Due to the low ductility of the material, laser beam welding at room temperature resulted in the formations of hot cracks. Sound butt joints without cracks were produced using pre-heating to T ≥ 600 °C. In the initial as-cast condition, the alloy consisted of coarse bcc grains with a small amount of lens-shaped C15 Laves phase particles. A columnar microstructure was formed in the welds; the thickness of the grains increased with the temperature of pre-heating before welding. The Laves phase particles were formed in the seams after welding at 600 °C or 800 °C, however, these particles were not observed after welding at room temperature or at 400 °C. Soaking at elevated temperatures did not change the microstructure of the base material considerably, however, “additional” small Laves particles formed at 600 °C or 800 °C. Tensile test of welded specimens performed at 750 °C resulted in the fracture of the base material because of the higher hardness of the welds. The latter can be associated with the bcc grains refinement in the seams. Full article

(This article belongs to the Special Issue High Entropy Materials: Challenges and Prospects)

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14 pages, 7764 KiB

Open AccessArticle

Compositional Design of Soft Magnetic High Entropy Alloys by Minimizing Magnetostriction Coefficient in (Fe_0.3Co_0.5Ni_0.2)_100−x(Al_1/3Si_2/3)_x System

by Yong Zhang, Min Zhang, Dongyue Li, Tingting Zuo, Kaixuan Zhou, Michael C. Gao, Baoru Sun and Tongde Shen

Metals 2019, 9(3), 382; https://doi.org/10.3390/met9030382 - 26 Mar 2019

Cited by 30 | Viewed by 5064

Abstract

Developing cost-effective soft magnetic alloys with excellent mechanical properties is very important to energy-saving industries. This study investigated the magnetic and mechanical properties of a series of (Fe_0.3Co_0.5Ni_0.2)_100−x(Al_1/3Si_2/3)_x high-entropy alloys [...] Read more.

Developing cost-effective soft magnetic alloys with excellent mechanical properties is very important to energy-saving industries. This study investigated the magnetic and mechanical properties of a series of (Fe_0.3Co_0.5Ni_0.2)_100−x(Al_1/3Si_2/3)_x high-entropy alloys (HEAs) (x = 0, 5, 10, 15, and 25) at room temperature. The Fe_0.3Co_0.5Ni_0.2 base alloy composition was chosen since it has very the smallest saturation magnetostriction coefficient. It was found that the (Fe_0.3Co_0.5Ni_0.2)₉₅(Al_1/3Si_2/3)₅ alloy maintains a simple face-centered cubic (FCC) solid solution structure in the states of as-cast, cold-rolled, and after annealing at 1000 °C. The alloy after annealing exhibits a tensile yield strength of 235 MPa, ultimate tensile strength of 572 MPa, an elongation of 38%, a saturation magnetization (Ms) of 1.49 T, and a coercivity of 96 A/m. The alloy not only demonstrates an optimal combination of soft magnetic and mechanical properties, it also shows advantages of easy fabrication and processing and high thermal stability over silicon steel and amorphous soft magnetic materials. Therefore, the alloy of (Fe_0.3Co_0.5Ni_0.2)₉₅(Al_1/3Si_2/3)₅ holds good potential as next-generation soft magnets for wide-range industrial applications. Full article

(This article belongs to the Special Issue High Entropy Materials: Challenges and Prospects)

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18 pages, 1408 KiB

Open AccessArticle

Intermetallic Phases in High-Entropy Alloys: Statistical Analysis of their Prevalence and Structural Inheritance

by Ming-Hung Tsai, Ruei-Chi Tsai, Ting Chang and Wen-Fei Huang

Metals 2019, 9(2), 247; https://doi.org/10.3390/met9020247 - 19 Feb 2019

Cited by 57 | Viewed by 6247

Abstract

Strengthening high entropy alloys (HEAs) via second phases is a very effective approach. However, the design of intermetallic (IM) phases in HEAs is challenging, mainly because our understanding of IM phases in HEAs is still very limited. Here, a statistical approach is used [...] Read more.

Strengthening high entropy alloys (HEAs) via second phases is a very effective approach. However, the design of intermetallic (IM) phases in HEAs is challenging, mainly because our understanding of IM phases in HEAs is still very limited. Here, a statistical approach is used to enhance our understanding towards IM phases in HEAs. A database consisting of 142 IM-containing HEAs was constructed. Our aim is twofold. The first is to reveal the most common IM phase types in published HEAs. The second is to understand whether HEAs inherit their IM structures from their binary/ternary subsystems, or whether they tend to form new structures irrelevant to their subsystems. The results show that the five most prevalent IM structures in the HEAs surveyed here are Laves, σ, B2, L1₂, and L2₁. This trend is evidently different from the overall trend among known binary/ternary IMs. As for structural inheritance, all the IM phases contained in the alloys are existing structures in the binary/ternary subsystems of the respective alloys. This suggests that the compositional complexity in HEAs does trigger additional complexity in IM structure formation. These findings have important implications in the future design and development of HEAs. Full article

(This article belongs to the Special Issue High Entropy Materials: Challenges and Prospects)

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Review

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16 pages, 2269 KiB

Open AccessFeature PaperReview

An Overview of High-Entropy Alloys as Biomaterials

by Diogo Castro, Pedro Jaeger, Ana Catarina Baptista and João Pedro Oliveira

Metals 2021, 11(4), 648; https://doi.org/10.3390/met11040648 - 15 Apr 2021

Cited by 67 | Viewed by 7950

Abstract

High-entropy alloys (HEAs) have been around since 2004. The breakthroughs in this field led to several potential applications of these alloys as refractory, structural, functional, and biomedical materials. In this work, a short overview on the concept of high-entropy alloys is provided, as [...] Read more.

High-entropy alloys (HEAs) have been around since 2004. The breakthroughs in this field led to several potential applications of these alloys as refractory, structural, functional, and biomedical materials. In this work, a short overview on the concept of high-entropy alloys is provided, as well as the theoretical design approach. The special focus of this review concerns one novel class of these alloys: biomedical high-entropy alloys. Here, a literature review on the potential high-entropy alloys for biomedical applications is presented. The characteristics that are required for these alloys to be used in biomedical-oriented applications, namely their mechanical and biocompatibility properties, are discussed and compared to commercially available Ti6Al4V. Different processing routes are also discussed. Full article

(This article belongs to the Special Issue High Entropy Materials: Challenges and Prospects)

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