Temperature-dependent yield stress of single crystals of non-equiatomic Cr-Mn-Fe-Co-Ni high-entropy alloys in the temperature range 10-1173 K

The temperature-dependent yield strengths of [123]-oriented single crystals of four quinary non-equiatomic CrMn-Fe-Co-Ni high-entropy alloys (HEAs) were investigated at temperatures of 10-1173 K. They exhibit similar trends with a rapid decrease of the critical resolved shear stress (CRSS) from 10 K to 300 K, followed by a much slower rate of decrease with increasing temperature and a plateau above 873 K. The HEAs with the highest and lowest Cr contents exhibit the highest and lowest yield strengths respectively at 10 K, but almost identical yield strengths at 300 K. Thus, at cryogenic temperatures, the magnitude of the temperature dependence of yield strength is positively correlated with Cr content. All the non-equiatomic HEAs also exhibit similar dislocation structures with planar arrays of smoothly-curved dislocations without any preferred orientations. Their stacking fault energy (SFE) decreases with increasing Cr content. An empirical expression is proposed to describe the composition dependence of SFE in the Cr-Mn-Fe-Co-Ni quinary system. A new route for optimizing the alloy design of non-equiatomic Cr-Mn-Fe-Co-Ni alloys in terms of strength and ductility through the combination of mean-square atomic displacement (MSAD) and SFE is discussed based on the results obtained.