Hardening and toughening effects of intermediate nanosized structures in a confined amorphous alloy film

Abstract

• Intermediate nanosized structure (termed as “nano shear bands” (NSBs)) between microscopic shear transformation zones (STZs) and macroscopic shear bands (SBs) was observed in the crystalline-layer confined amorphous (CLCA) NiW alloy films. • NSBs promoted multiple and controlled shear banding deformation, hence leading to the enhanced crystallization. • NSBs possessed both hardening and toughening effects for the CLCA films. The plastic deformation of amorphous alloys is well known to be localized into shear bands (SBs), which are believed to stem from the atomic-scale flow defects, i.e., shear transformation zones (STZs). Yet, the bridge between the mesoscopic SBs and the atomic-scale STZs remains poorly understood. In this work, through thermally activating pronounced β relaxations in the well-designed crystalline-layer confined amorphous (CLCA) NiW alloy films, we experimentally captured and observed an intermediate nanosized structure termed as “nano shear bands” (NSBs) with a typical size of 1–2 nm in thickness and 5–10 nm in length. The influences of such NSB structures on the macroscale deformation behavior were systematically investigated. It was found that NSBs lead to both hardening and toughening effects for the CLCA films, as they promote multiple and controlled shear banding deformation, which results in enhanced crystallization. The intermediate NSB structure could connect the microstructural characteristics and macroscopic plasticity in amorphous alloys and may provide new insights for understanding the microscopic deformation mechanism of amorphous alloys as well as tuning/designing their properties.