Repetitive Ultra-low Stress Induced Nanocrystallization in Amorphous Cu‒Zr‒Al Alloy Evidenced by in situ Nanoindentation

Abstract

Stress driven nucleation of nanocrystals in amorphous alloys has been a subject of intensive debate in the past decade. It has long been postulated that nanocrystals form succeeding the occurrence of shear bands in deformed amorphous alloys. In this study, we show, via in situ nanoindentation of amorphous Cu44Zr44Al12 alloy in a transmission electron microscope that the formation of nanocrystals occurred at an ultra-low stress of 0.25 GPa in the elastic deformation regime, accompanied by load-drops without evidence of shear bands. Furthermore, during successive loading, repetitive nanocrystal nucleation events were observed, and the stress required for nucleation kept on increasing to ∼0.54 GPa, implying the occurrence of a ‘hardening’ effect in the amorphous alloy. This study provides direct evidence to advance our understanding on deformation-induced nanocrystallization of amorphous alloys.