Microstructure and Mechanical Properties of High-Entropy Alloy Co20Cr26Fe20Mn20Ni14 Processed by High-Pressure Torsion at 77\u2009K and 300\u2009K

Jongun Moon,Yuri Estrin,Soo-Hyun Joo,Aleksey Podolskiy,Yuanshen Qi,Mikhail Tikhonovsky,Elena Tabachnikova,Byeong-Joo Lee,Hyoung Seop Kim,Won-Mi Choi

doi:10.1038/s41598-018-29446-y

Abstract

In this work, the mechanical characteristics of high-entropy alloy Co20Cr26Fe20Mn20Ni14 with low-stacking fault energy processed by cryogenic and room temperature high-pressure torsion (HPT) were studied. X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses were performed to identify the phase and microstructure variation and the mechanical properties characterized by Vickers hardness measurements and tensile testing. Cryogenic HPT was found to result in a lower mechanical strength of alloy Co20Cr26Fe20Mn20Ni14 than room temperature HPT. Microstructure analysis by SEM and TEM was conducted to shed light on the microstructural changes in the alloy Co20Cr26Fe20Mn20Ni14 caused by HPT processing. Electron microscopy data provided evidence of a deformation-induced phase transformation in the alloy processed by cryogenic HPT. Unusual softening phenomena induced by cryogenic HPT were characterized by analyzing the dislocation density as determined from X-Ray diffraction peak broadening.

Highlights

Since the inception of the concept of HEAs, numerous studies have been conducted to characterize their mechanical properties and microstructure evolution, of coarse-grained HEAs16–18
As the holding time after High-pressure torsion (HPT) at room temperature increased from one day to one month, a decrease in Vickers hardness was not observed
This ensures the stability of microstructure and mechanical properties after HPT processing at room temperature

Summary

Introduction

Since the inception of the concept of HEAs, numerous studies have been conducted to characterize their mechanical properties and microstructure evolution, of coarse-grained HEAs16–18. Nanocrystalline states were produced in a single phase CoCrFeMnNi HEA using HPT at ambient temperature[22] It was shown by tensile testing[22] that a transition to a nanocrystalline structure gives rise to a significant increase of the room temperature strength accompanied with moderate ductility. It is of great interest to produce a nanocrystalline or UFG structure in the CoCrFeMnNi HEA by cryogenic HPT (‘cryo-HPT’) and to study the effect of the processing temperature on its microstructure and the mechanical properties. The present follow-up work investigates the microstructure and mechanical properties of the Co20Cr26Fe20Mn20Ni14 alloy processed by HPT at both liquid nitrogen temperature and room temperature have been investigated The results of this in-depth investigation are reported below

Methods

Results

Conclusion