Interparticle bonding and interfacial nanocrystallization mechanisms in additively manufactured bulk metallic glass fabricated by cold spray

Amorphous Zr-based bulk metallic glass deposit was produced by cold spray additive manufacturing. The bonding mechanism of metallic glass particles was systematically investigated through studying the deformation behavior of individual particles after deposition. We revealed two collective particle bonding mechanisms that contributed to the formation of metallic glass deposits, i.e., high-velocity impact induced localized metallurgical bonding at the fringe of the interface, and high particle temperature induced viscosity reduction and the resultant annular metallurgical bonding band. Moreover, the dynamic evolution mechanism of the amorphous phase into nanocrystal structures at severely deformed interfacial regions during cold spray was carefully investigated. For the first time, we observed different amorphous/nanocrystal structures in cold sprayed metallic glass deposits, which can represent different evolution stages in nanocrystallization process. Based on the observation, it is inferred that the nanocrystallization process can be divided into following three stages: composition segregation, the formation of ordered 1D and 2D transition structures, and 3D nanocrystals. The current study provides new insights into the bonding mechanisms and the mechanistic nanocrystallization origins in cold sprayed bulk metallic glass deposits.