Structural heterogeneity in 3D printed Zr-based bulk metallic glass by selective laser melting

Abstract

Bulk metallic glasses (BMGs) have attracted increasing attention in past two decades owing to unique properties over their crystalline counterparts. However, the challenge in manufacturing of BMGs significantly blocks the applications of this new type of metallic materials. The 3D printing technique of selective laser melting (SLM) provides a promising route to the manufacture of BMG components with desirable geometries. While the complicated thermal history in SLM process generally induce structural heterogeneities of the 3D-printed BMG components, and this issue remains elusive. Here, the detailed microstructure of 3D printed Zr55Cu30Al10Ni5 BMG was systemically investigated. The results revealed significant structural heterogeneities in the as-printed Zr-based BMG: fully amorphous structure in molten pools, while mixed amorphous phase with nanocrystals were presented in heat affected zones (HAZs). More interesting finding is that the amorphous phase in molten pools and HAZs has quite different features, as verified by different compositions and different crystallization kinetics. Partial crystallization in HAZs due to repeated laser scanning in SLM process causing composition shift can account for the different behaviors of the amorphous phases in the two regions. The present work provides an in-depth understanding on the structural heterogeneities and different kinetic behaviors of the 3D printed BMGs.