Discovery Of High-entropy Alloys Research Articles

Hot isostatic pressing of ball milled novel grade high entropy alloys at different sintering time and the investigation of their mechanical and corrosion resistance properties

Abstract With the discovery of high entropy alloys, new materials with superior properties have emerged. According to recent research, high-entropy alloys’ multi-component structure and mixing entropy have made them more prominent than other alloys. Because of their excellent chemical and mechanical properties—such as high hardness, high-temperature resistance, high wear resistance, chemical stability, and high corrosion resistance—high entropy alloys outperform other material types in various applications. A new grade of mechanically alloyed high entropy alloy (HEA) of composition 23Fe-21Cr-18Ni-20Ti-18Mn was consolidated by a hot isostatic pressing (HIP) at a temperature of 1000 °C, at different sintering time of 30, 60, and 90 min respectively. We have investigated the impact of sintering time on the microstructure, mechanical, corrosion, and wear-resistance properties. The x-ray diffraction (XRD) spectra of the 30 min HIPed HEA sample showed dominant s-FeCr phases and traces of γ-Fe, and the Ni-Ti phases. Whereas, the 90 min HIPed HEA samples showed more dominant Ni-Ti and traces of γ-Fe, and β-Mn phases. There is a phase transformation from BCC to HCP of consolidated HEA at increased holding time. The density of the samples increases from 5.882 to 6.327 g cm−3 and the porosity percentage decreases from 12.93 to 6.35% with the increase in the holding time. The Vickers microhardness value for 30, 60, and 90 min HIPed 23Fe-21Cr-18Ni-20Ti-18Mn HEA at 1000 °C was found to be 433, 513, and 793 HV respectively at an indentation load of 0.1 kgf. The consolidated HEA sample undergoes an abrasive and oxidative wear mechanism with ploughing and plastic deformation modes. The morphology of the wear debris was investigated using SEM. The 90 min sintered sample showed an excellent corrosion resistance due to the high rate of material densification and minimum surface flaws.

High Entropy Oxides: Mapping the Landscape from Fundamentals to Future Vistas: Focus Review.

High-entropy materials (HEMs) are typically crystalline, phase-pure and configurationally disordered materials that contain at least five elements evenly blended into a solid-solution framework. The discovery of high-entropy alloys (HEAs) and high-entropy oxides (HEOs) disrupted traditional notions in materials science, providing avenues for the exploration of new materials, property optimization, and the pursuit of advanced applications. While there has been significant research on HEAs, the creative breakthroughs in HEOs are still being revealed. This focus review aims at developing a structured framework for expressing the concept of HEM, with special emphasis on the crystal structure and functional properties of HEOs. Insights into the recent synthetic advances, that foster prospective outcomes and their current applications in electrocatalysis, and battery, are comprehensively discussed. Further, it sheds light on the existing constraints in HEOs, highlights the adoption of theoretical and experimental tools to tackle challenges, while delineates potential directions for exploration in energy application.

Fundamental design strategies for advancing the development of high entropy alloys for thermo-mechanical application: A critical review

Nearly three decades since the discovery of high entropy alloys (HEAs), it has greeted a broad interest in the field of materials research as a better alternative to conventional alloy materials due to the exceptional combinatorial properties they offer in terms of lightweight, high-specific strength in elevated temperatures, excellent oxidation and corrosion resistance properties (among others). Leveraging on the “four core effects”: high-entropy effect, sluggish/hysteretic diffusion effect, severe-lattice-distortion effect and cocktail effect which define the special features responsible for their outstanding properties, HEAs have been successfully employed for high-temperature applications in automobile and in the aerospace. An emerging sub-field of HEAs is the incorporation of a secondary strengthening phase that can be provided by the precipitation of intermetallic (IM) compounds to enhance the microstructure which will concomitantly affect the properties of a material (thermal, chemical and mechanical properties) for broader engineering applications. In this article, design concepts brewed from thermo-physical parameters calculation and computational thermodynamics using a CALPHAD-based tool were reviewed as fundamental design strategies in the development of IM-containing HEAs.

Deformation behavior of high-entropy oxide (Mg,Co,Ni,Cu,Zn)O under extreme compression

Following the discovery of high-entropy alloys, high-entropy oxides have gained considerable interest due to their unconventional structural characteristics and versatile functional properties for promising applications. Via synchrotron radial x-ray diffraction in a diamond anvil cell, the mechanical strength and deformation behavior of a typic high-entropy oxide (Mg,Co,Ni,Cu,Zn)O with a rock-salt structure under extreme compression has been investigated in situ. This compound in a polycrystalline state shows a large elastic anisotropy at the initial compression stage and then gradually becomes isotropic at around 21.4 GPa, similar with the behavior of MgO. Based on the lattice strain order conversion and texture evolution under compression, a dominant slip system transition from {100}<011> to {110}<1–10> is proposed in this high-entropy oxide. This work deepens our understanding on the role of chemical disorder in the mechanical properties of entropy-stabilized oxides, which would be indispensable to the design of advanced structural ceramics with optimal strength-to-ductility ratio.

A FRESH PERSPECTIVE ON MEDIUM ENTROPY ALLOYS APPLICATIONS AS COATING AND COATING SUBSTRATE

In order to evolve as a society we need increasingly efficient technologies and implicitly materials with great performance that promote safety and sustainability. The discovery of high entropy alloys was received with much enthusiasm due to the possibility of designing new materials with improved properties, that could be used in applications that require extreme conditions or a very specific combination of properties. As the research in this area is continuously increasing and the results are very promising, this review focuses on the most recent investigations on medium entropy alloys (MEAs) applications, highlighting their properties, but taking into consideration other factors, such as economic and environmental factors. Additionally, considering the high cost associated with MEAs fabrication, MEA coatings are also explored, as they are nowadays regarded as a more convenient procedure to obtain the required properties for various substrate materials.

Novel method for automatic search for stable ordered phases in multicomponent systems

The discovery of high entropy alloys (HEAs) dramatically increased the number of new commercial materials. Today, multicomponent systems are some of the main objects of research in the field of materials science. However, their chemical complexity significantly complicated the materials modeling, so conventional simulations techniques are hardly applicable. In this paper, we propose a rapid high-throughput approach for an automatic detection for stable ordered structures in multicomponent alloys. High computational efficiency is achieved through the use of a novel low-rank interatomic potential. The approach was verified on several binary temperature-concentration phase diagrams. Then it was applied to search for secondary phases in CoFeNiCr, which is believed to be a single-phase high-entropy alloy. As a result, we detected the ordering of Ni and Cr in CoFeNiCr and similar alloys in a wide range of temperatures and compositions.

Pushing the limits of magnetocaloric high-entropy alloys

High-entropy alloys (HEAs) have become a topic of high research interest due to the excellent mechanical properties that can be found in this new type of materials. However, their functional properties are usually modest when compared to conventional materials. The discovery of high-entropy alloys with an optimal combination of mechanical and functional properties would be a leap forward in the reliability of devices that use them as functional elements. This Research Update focuses on magnetocaloric HEAs, showing that a directed search strategy allows us to improve their performance in a significant way, closing the pre-existing gap between magnetocaloric HEAs and high-performance magnetocaloric materials. Further challenges that remain in this line of research are highlighted.

Microstructural evolution and mechanical properties of FeCoCrNiCu high entropy alloys: a microstructure-based constitutive model and a molecular dynamics simulation study

High entropy alloys (HEAs) attract remarkable attention due to the excellent mechanical performance. However, the origins of their high strength and toughness compared with those of the traditional alloys are still hardly revealed. Here, using a microstructure-based constitutive model and molecular dynamics (MD) simulation, we investigate the unique mechanical behavior and microstructure evolution of FeCoCrNiCu HEAs during the indentation. Due to the interaction between the dislocation and solution, the high dislocation density in FeCoCrNiCu leads to strong work hardening. Plentiful slip systems are stimulated, leading to the good plasticity of FeCoCrNiCu. The plastic deformation of FeCoCrNiCu is basically affected by the motion of dislocation loops. The prismatic dislocation loops inside FeCoCrNiCu are formed by the dislocations with the Burgers vectors of {a over 6}left[ {bar 11bar 2} right] and {a over 6}left[ {1bar 12} right], which interact with each other, and then emit along the 〈111〉 slip direction. In addition, the mechanical properties of FeCoCrNiCu HEA can be predicted by constructing the microstructure-based constitutive model, which is identified according to the evolution of the dislocation density and the stress-strain curve. Strong dislocation strengthening and remarkable lattice distortion strengthening occur in the deformation process of FeCoCrNiCu, and improve the strength. Therefore, the origins of high strength and high toughness in FeCoCrNiCu HEAs come from lattice distortion strengthening and the more activable slip systems compared with Cu. These results accelerate the discovery of HEAs with excellent mechanical properties, and provide a valuable reference for the industrial application of HEAs.

Nanomechanical studies of high-entropy alloys

Abstract

In-Situ Imaging of Liquid Phase Separation in Molten Alloys Using Cold Neutrons

Understanding the liquid phases and solidification behaviors of multicomponent alloy systems becomes difficult as modern engineering alloys grow more complex, especially with the discovery of high-entropy alloys (HEAs) in 2004. Information about their liquid state behavior is scarce, and potentially quite complex due to the presence of perhaps five or more elements in equimolar ratios. These alloys are showing promise as high strength materials, many composed of solid-solution phases containing equiatomic CoCrCu, which itself does not form a ternary solid solution. Instead, this compound solidifies into highly phase separated regions, and the liquid phase separation that occurs in the alloy also leads to phase separation in systems in which Co, Cr, and Cu are present. The present study demonstrates that in-situ neutron imaging of the liquid phase separation in CoCrCu can be observed. The neutron imaging of the solidification process may resolve questions about phase separation that occurs in these alloys and those that contain Cu. These results show that neutron imaging can be utilized as a characterization technique for solidification research with the potential for imaging the liquid phases of more complex alloys, such as the HEAs which have very little published data about their liquid phases. This imaging technique could potentially allow for observation of immiscible liquid phases becoming miscible at specific temperatures, which cannot be observed with ex-situ analysis of solidified structures.