Formation and Disruption of W-Phase in High-Entropy Alloys

Kirill Yusenko,Ronald Clark,Stephen Brown,Nicholas Lavery,Chung Fung,Justin Searle,Sephira Riva

doi:10.3390/met6050106

Abstract

High-entropy alloys (HEAs) are single-phase systems prepared from equimolar or near-equimolar concentrations of at least five principal elements. The combination of high mixing entropy, severe lattice distortion, sluggish diffusion and cocktail effect favours the formation of simple phases—usually a bcc or fcc matrix with minor inclusions of ordered binary intermetallics. HEAs have been proposed for applications in which high temperature stability (including mechanical and chemical stability under high temperature and high mechanical impact) is required. On the other hand, the major challenge to overcome for HEAs to become commercially attractive is the achievement of lightweight alloys of extreme hardness and low brittleness. The multicomponent AlCrCuScTi alloy was prepared and characterized using powder X-ray diffraction (PXRD), scanning-electron microscope (SEM) and atomic-force microscope equipped with scanning Kelvin probe (AFM/SKP) techniques. Results show that the formation of complex multicomponent ternary intermetallic compounds upon heating plays a key role in phase evolution. The formation and degradation of W-phase, Al2Cu3Sc, in the AlCrCuScTi alloy plays a crucial role in its properties and stability. Analysis of as-melted and annealed alloy suggests that the W-phase is favoured kinetically, but thermodynamically unstable. The disruption of the W-phase in the alloy matrix has a positive effect on hardness (890 HV), density (4.83 g·cm−3) and crack propagation. The hardness/density ratio obtained for this alloy shows a record value in comparison with ordinary heavy refractory HEAs.

Highlights

Ever since their discovery, high-entropy alloys (HEAs) have become one of the major research topics in materials engineering
We focus on the key role played by multicomponent intermetallic compounds in the phase formation of equimolar High-entropy alloys (HEAs) containing elements likely to form complex ordered binary and especially ternary phases, such as Al, Cu and Sc [11]
It has been shown for a number of Al‐based alloys containing minor Sc and Cu additions that a. It has beenmicrostructural shown for a number alloys containing and Cu additions that noticeable feature is of theAl-based appearance of a ternary phaseminor havingSc a ThMn

Summary

Introduction

High-entropy alloys (HEAs) have become one of the major research topics in materials engineering. Outstanding mechanical and structural features, coupled with simple crystal structures, make HEAs promising as materials for high-temperature applications, in which high hardness should be coupled with high chemical and mechanical stability [1]. According to their density, melting point and hardness, HEAs can be classified as heavy/light, refractory, soft/hard materials. Only few alloys display micro-hardness values of 800 HV or more. Such hardness values have usually been obtained for refractory HEAs (such as MoTiVFeNiZrCoCr) or for light

Methods

Discussion

Conclusion