Selective laser melting vitrification of amorphous soft magnetic alloys with help of double-scanning-induced compositional homogeneity

Abstract

Recently, selective laser melting (SLM) of Fe-based soft magnetic bulk metallic glass (BMG) is garnering great attention because it can yield both superior magnetic properties such as high permeability and low core loss and near-net shaping of 3-dimensional complex components. However, full vitrification of BMGs with high saturation magnetization above 1.2 T has never been realized because cooling rates are limited and compositional inhomogeneity induced by rapid laser processing causes severe undesirable crystallization. In this work, a double scan strategy has been employed with the aim of amorphous phase fraction enhancement as well as densification. We have shown that double scanning effectively fills voids generated due to partial melting of powders, and leads to relative density of up to 96% and corresponding saturated magnetization of 1.22 T. More importantly, the double scan strategy stimulates reflow in the melt pool, securing compositional uniformity, and eventually enhances amorphous phase fraction to a value as high as 47%. As a consequence, coercivity has been significantly decreased, which in turn reduces core loss and increases permeability.