Investigation on the incipient plasticity of 〈001〉-oriented CoCrFeNi micropillar

Abstract

Micro-level mechanical tests are of extreme sensitivity to the initial internal state and early response of materials. The stability of elastic property and yield behavior of macro-level polycrystal specimens fade significantly under micro-level uniaxial loading state. In this study, the incipient plasticity and underlying mechanisms of medium-entropy alloy CoCrFeNi were investigated by in-situ micropillar compression. Stress fluctuations at elastic stage of 〈001〉-oriented pillar were observed in the stress-strain curves and then evidenced by TEM characterization as the activation of leading partial dislocations. The discreteness of yield strength was thus attributed to the impediment of pre-formed stacking faults. Furthermore, a model illustrating the incipient plasticity and its consequences on micropillar compression tests was proposed after an evaluation on twinning stress of alloys with low stacking fault energy.