Microstructure, Texture, and Strength Development during High-Pressure Torsion of CrMnFeCoNi High-Entropy Alloy

Werner Skrotzki,Eva Odor,Aurimas Pukenas,Reinhard Pippan,Bernhard Völker,Easo P George,Bertalan Joni,Tamas Ungar,Anton Hohenwarter

doi:10.3390/cryst10040336

Abstract

The equiatomic face-centered cubic high-entropy alloy CrMnFeCoNi was severely deformed at room and liquid nitrogen temperature by high-pressure torsion up to shear strains of about 170. Its microstructure was analyzed by X-ray line profile analysis and transmission electron microscopy and its texture by X-ray microdiffraction. Microhardness measurements, after severe plastic deformation, were done at room temperature. It is shown that at a shear strain of about 20, a steady state grain size of 24 nm, and a dislocation density of the order of 1016 m−2 is reached. The dislocations are mainly screw-type with low dipole character. Mechanical twinning at room temperature is replaced by a martensitic phase transformation at 77 K. The texture developed at room temperature is typical for sheared face-centered cubic nanocrystalline metals, but it is extremely weak and becomes almost random after high-pressure torsion at 77 K. The strength of the nanocrystalline material produced by high-pressure torsion at 77 K is lower than that produced at room temperature. The results are discussed in terms of different mechanisms of deformation, including dislocation generation and propagation, twinning, grain boundary sliding, and phase transformation.

Highlights

High-entropy alloys (HEAs) represent a new class of single-phase multi-element (≥5) solid solution alloys with near-equiatomic concentrations of the individual elements [1]
The present paper extends recent work of the authors on microstructure and texture development of CrMnFeCoNi HEA processed by high-pressure torsion (HPT) at room temperature (RT) [13]
The most striking feature observed by X-ray diffraction (XRD) is the phase transformation from face-centered cubic (FCC) to hexagonal close-packed (HCP) at LNT (Figure 1)

Summary

Introduction

High-entropy alloys (HEAs) represent a new class of single-phase multi-element (≥5) solid solution alloys with near-equiatomic concentrations of the individual elements [1]. Among the wide variety of reported HEAs with simple crystal structures, such as face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close-packed (HCP), the most thoroughly investigated alloy is the quinary equiatomic FCC HEA CrMnFeCoNi [2] often referred to as Cantor alloy. I.e., increasing deviatoric stress, the onset pressure decreases, while for decreasing grain size it increases These results are in agreement with finite-temperature ab initio calculations showing that the HCP structure is energetically favored at low temperatures [8,9,10]

Results

Discussion

Conclusion