Hardening and thermal stability of a nanocrystalline CoCrFeNiMnTi0.1 high-entropy alloy processed by high-pressure torsion

H Shahmir,M Nili-Ahmadabadi,A Shafie,Tg Langdon

doi:10.1088/1757-899x/194/1/012017

Abstract

A CoCrFeNiMnTi0.1 high-entropy alloy (HEA) was subjected to high-pressure torsion (HPT) processing under 6.0 GPa pressure up to 10 turns. XRD results reveal that the initial and HPT-processed microstructures consist of a single fcc phase and there is no evidence for creating a new phase and the occurrence of a phase transformation during HPT processing. It is shown that there is a gradual evolution in hardness with increasing numbers of turns but full homogeneity is not achieved even after 10 turns. Microhardness measurements reveal that the material reaches a saturation hardness value of Hv ≈ 460 which is approximately three times higher than for the homogenized alloy. The nanostructured HEA was subjected to post-deformation annealing (PDA) at 473-1173 K and it is shown that the hardness increases slightly up to Hv ≈ 550 at 773 K due to a phase decomposition and the formation of new precipitates and then decreases to the hardness of the homogenized sample (Hv ≈ 140) at 1173 K due to a combination of recrystallization, grain growth and dissolution of the precipitates. The results reveal that an addition of only 2 at.% Ti will improve the hardness and thermal stability of the nanocrystalline CoCrFeNiMn HEA.

Highlights

High entropy alloys (HEAs) have attracted worldwide attention due to their potential beneficial mechanical and electrochemical characteristics, such as high strength, high thermal stability and oxidation resistance
Hardening after high-pressure torsion (HPT) Processing The results for the corresponding Vickers microhardness measurements are shown in Fig. 1(a) after processing through different numbers of turns with the average values of Hv plotted along each disk diameter and with the lower dashed line at Hv ≈ 140 corresponding to the initial hardness in the homogenized condition
Summary and conclusions A CoCrFeNiMnTi0.1 high-entropy alloy was processed by HPT under 6.0 GPa pressure up to 10 turns at room temperature

Summary

Introduction

High entropy alloys (HEAs) have attracted worldwide attention due to their potential beneficial mechanical and electrochemical characteristics, such as high strength, high thermal stability and oxidation resistance. Processing the CoCrFeNiMn high-entropy alloy by HPT leads to significant hardening and grain refinement and post deformation annealing (PDA) of such a nanocrystalline CoCrFeNiMn HEA provides a combination of high strength and good ductility including an ultimate tensile strength [15]. Hardening after HPT Processing The results for the corresponding Vickers microhardness measurements are shown in Fig. 1(a) after processing through different numbers of turns with the average values of Hv plotted along each disk diameter and with the lower dashed line at Hv ≈ 140 corresponding to the initial hardness in the homogenized condition.

Results

Conclusion