Decoding deformation-induced phase transformation in a high entropy alloy via nanoindentation pop-in phenomenon

Abstract

Three high-entropy alloys (HEAs) exhibiting austenite-to-martensite (γ→ϵ) transformation with composition-dependent metastability variation were nanoindented. The incipient γ→ϵ transformation is elastic stress-induced and occurred via monopartial stacking, resulting in distinctive displacement pop-in phenomenon. The number of monopartials was directly correlated with alloy metastability as interpreted from pop-in width. Metastability plus configuration of {111} planes relative to the indentation axis determined the critical pop-in force, which impacted mechanical activation energy and radial scale of transformation volume. Metastability also influenced recovery as examined from unloading portion of force-displacement curve. These nanoindentation findings offer key insights into phase transformation of HEAs in crystal scale.