Evolution of Microstructure and Mechanical Properties of a CoCrFeMnNi High-Entropy Alloy during High-Pressure Torsion at Room and Cryogenic Temperatures

Sergey Zherebtsov,Margarita Klimova,Yulia Ivanisenko,Nikita Stepanov,Dmitry Shaysultanov,Nikita Yurchenko,Gennady Salishchev

doi:10.3390/met8020123

Sergey Zherebtsov, Margarita Klimova + Show 5 more

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https://doi.org/10.3390/met8020123

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Abstract

High-pressure torsion (HPT) is applied to a face-centered cubic CoCrFeMnNi high-entropy alloy at 293 and 77 K. Processing by HPT at 293 K produced a nanostructure consisted of (sub)grains of ~50 nm after a rotation for 180°. The microstructure evolution is associated with intensive deformation-induced twinning, and substructure development resulted in a gradual microstructure refinement. Deformation at 77 K produces non-uniform structure composed of twinned and fragmented areas with higher dislocation density then after deformation at room temperature. The yield strength of the alloy increases with the angle of rotation at HPT at room temperature at the cost of reduced ductility. Cryogenic deformation results in higher strength in comparison with the room temperature HPT. The contribution of Hall–Petch hardening and substructure hardening in the strength of the alloy in different conditions is discussed.

Highlights

The concept of high-entropy alloys (HEAs) as a mixture of more than five metallic elements in equimolar proportions was proposed first by Yeh et al in 2004 [1]
It was found that the CoCrFeMnNi alloy demonstrated very high elongation (7080%), but rather low yield strength of 200 MPa at room temperature [6,7]
An SEM-back-scattered electron (BSE) image shows a homogeneous microstructure with a grain size of ~15 μm Numerous Numerous annealing twins were twins foundwere inside grains

Summary

Introduction

The concept of high-entropy alloys (HEAs) as a mixture of more than five metallic elements in equimolar proportions was proposed first by Yeh et al in 2004 [1]. It was found that the CoCrFeMnNi alloy demonstrated very high elongation (7080%), but rather low yield strength of 200 MPa at room temperature [6,7]. A reduction of a grain size from 150 to 5 μm in the CoCrFeMnNi alloy increased the yield strength by a factor of two while maintained good ductility [6]. Severe plastic deformation of the CoCrFeNiMn alloy via high-pressure torsion (HPT) expectably refined the microstructure to a grain size d~40–50 nm and increased the microhardness of the alloy by a factor of ~3 [8,9,10]. The ultimate tensile strength of the alloy after HPT was found to be ~2000 MPa [8]

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