Atomic-level understanding of crystallization in the selective laser melting of Fe50Ni50 amorphous alloy

Selective laser melting (SLM), an emerging technology, has enabled the fabrication of large Fe-based amorphous alloys (FAAs) with complex geometry, unlocking the potential for the wider implementation. However, the almost unavoidable crystallization during SLM greatly degrades the performance of SLM fabricated FAAs. This study aims to understand the crystallization mechanism by investigating the atomic crystallization and cluster evolution in Fe50Ni50 FAA using molecular dynamics simulation under various laser powers and scanning speeds. It is observed that crystallization occurs easily at low scanning speed due to the increased fractions of body-centered cubic (BCC) bond pairs 1661 and 1441, with corresponding Voronoi polyhedrons <0,6,0,8> and <0,5,2,6>. The ease of crystallization is interpreted by increasing laser energy density, determined by elevating laser power and lowering scanning speed. Additionally, the suppression of crystallization is explained by the increasing average temperature variation rate, while effectively shortening the relaxation time for atomic rearrangement, inhibiting the increase of BCC crystal phases. This research is conducive to comprehend relevant atomic-level information on crystallization mechanism and microstructure evolution and provides an alternative way to inhibit crystallization during the manufacture FAAs with SLM.