Crystallization during laser powder bed fusion of the Finemet soft magnetic glass-forming alloy

Abstract

This study investigates crystallization phenomena during laser powder bed fusion (LPBF) of the soft magnetic, glass-forming Finemet® alloy. Cuboidal specimens were fabricated using a double-scan strategy, in which the scan speed of the second pass was varied to tailor local thermal conditions. The resulting microstructures were characterized using optical, scanning, and transmission electron microscopy, while thermal histories were modeled through finite element (FEM) simulations. The results are interpreted within the framework of classical nucleation and growth theory. The LPBF-processed material exhibits a mixed amorphous–crystalline microstructure, with equiaxed crystallites predominantly formed by partial devitrification of previously deposited amorphous regions. These equiaxed grains resemble those produced during the devitrification of melt-spun ribbons, being enriched in Fe and Si, depleted in Nb and B, and displaying a DO₃ structure. However, their size distribution is substantially broader, ranging from a few tens to several hundred nanometers. This gradient, coarse microstructure is attributed to the extreme thermal conditions inherent to LPBF, which vary locally within the heat-affected zone, and to the reduced Cu cluster density resulting from rapid solidification. Additionally, a minor population of dendritic crystals develops at the melt pool peripheries during solidification, with their size decreasing as scan speed increases, consistent with higher FEM-simulated cooling rates. Precise tailoring of the amorphous–crystalline microstructure is key to the integration of the investigated material into complex-shaped components for energy applications.