Surface gradient heterogeneity induced tensile plasticity in a Zr-based bulk metallic glass through ultrasonic impact treatment

Abstract

The excellent mechanical properties of bulk metallic glasses (BMGs) ensure them as a potential engineering material, however, the brittle nature; especially nil tensile plasticity restricts their engineering applications. Ductile phase precipitation is confirmed as an effective way to improve the BMG's plasticity; nevertheless, it is at the expense of BMG's strength due to the low strength of ductile phases. In this paper, ultrasonic impact treatment (UIT) was applied to Zr63.78Cu14.72Ni8Co2Al10Nb1.5 bulk metallic glasses and obvious tensile yield platforms, i.e., tensile plasticity, were obtained, regardless of zero tensile plasticity for the as-cast one. The samples after 4 or 8 runs UIT show a 1.1-1.2% plastic deformation. UIT ensures the BMGs more stable with more endothermic enthalpy in glass transition zone and separated structure with hard and soft regions. A surface gradient heterogeneity caused by UIT is responsible for a favorable shearing path and apparent tensile plasticity.