Crystallization behavior of Zr₅₅Cu₃₀Al₁₀Ni₅ amorphous alloys produced by selective laser melting of preannealed powders

Selective laser melting (SLM) of Zr₅₅Cu₃₀Al₁₀Ni₅ (Zr55) bulk metallic glasses (BMGs) with Zr55 original unannealed powders and annealed powders has been investigated, which is an effort to reveal the influence of crystallization state of powders on the crystallization behavior of remelted zone (RZ) and heat affected zone (HAZ). The as-prepared Zr55 powders consist of amorphous matrix and Al₅Ni₃Zr₂-type phase. When the Zr55 origin powders are annealed at 600 K, 800 K and 1000 K, the microstructure of amorphous matrix is transformed into amorphous, metastable + stable phases and entirely stable phases, respectively. After SLM of these different powders, the gradient microstructure with three crystalline zones (nanocrystal, dendritic eutectic, spherulite) is found from RZ to HAZ for all the deposits. However, the size and density of dendritic eutectic in the top of HAZ is much smaller for the deposits prepared by annealed powders than that by the unannealed powders. In contrast to top of HAZ, abundant multiphase spherulites are formed at the bottom of HAZ for the deposits prepared by the powders with or without annealed. The detailed microstructural and numerical model results reveal that the crystallization at the top of HAZ is mainly dominated by the rapid growth of quench-in clusters or nuclei in RZ, but the crystallization at the bottom of HAZ is controlled by both the nucleation and growth of these clusters or nuclei. It is precisely because the average size of quench-in clusters or nuclei increases but total quantity decreases during annealing, resulting in the increase of thermal stability in RZ and the suppression of crystallization in the top of HAZ for the deposits with annealed powders.