INDENTATION SIZE EFFECT IN HIGH PRESSURE TORSION PROCESSED HIGH ENTROPY ALLOY

Petr Haušild,Jiří Zýka,Jakub Čížek,Jaroslav Čech,Hyoung Seop Kim

doi:10.14311/app.2020.27.0141

Abstract

High entropy alloy HfNbTaTiZr in as cast conditions and after high pressure torsion straining was characterized by nanoindentation. The length-scale dependent material response (indentation size effect) was characterized by indentation at various indentation depths. Hardness dependence on the characteristic length (depth of penetration) indicated decomposition of disordered high entropy alloy in the as cast sample, which probably occurred during slow cooling after casting. Subsequent severe plastic deformation by high pressure torsion led on the other hand to the short-range disorder of (originally partially decomposed as cast) structure. Further hardening was generated during high pressure torsion by the mechanisms of grain refinement and increasing dislocation density.

Highlights

In high entropy alloys (HEAs), the configurational entropy of a multicomponent solid solution phase is maximized so that the Gibbs energy of random solution may be lower than that of possible intermetallic phases
Indentation Size Effect in high pressure torsion (HPT) Processed High Entropy Alloy depth dependence of the hardness H can be related to the characteristic length h∗ through the relation: H
The hardness in the limit of infinite depth H0 is increasing with the increasing level of HPT straining (HPT leads to the strain hardening [13])

Summary

Introduction

In high entropy alloys (HEAs), the configurational entropy of a multicomponent solid solution phase is maximized so that the Gibbs energy of random solution may be lower than that of possible intermetallic phases. The HEAs show promising mechanical properties in applications ranging from (high temperature) structural to biocompatible materials [2, 3]. Mechanical properties of such alloys can further be improved by grain refinement especially by severe plastic deformation. An increase of strength with decreasing grain size was achieved through processing by high pressure torsion (HPT) in the probably most investigated HEA - Cantor alloy i.e., equiatomic CoCrFeMnNi with face-centered cubic (fcc) structure [4]

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Conclusion