Laser powder bed fusion of an Fe-based metallic glass using time delays

Abstract

Laser powder bed fusion (LPBF) of dense and fully amorphous commercial Fe-based metallic glass (MG) alloys, such as Kuamet 6B2, remains challenging when using simple scanning strategies. High-energy conditions produce dense but highly crystalline samples, while low-energy conditions led to higher amorphous fractions and reduced density. This study investigates the impact of introducing a controlled laser-off period ("time delay," tOFF) after each scan track in an LPBF meander scanning strategy on the processability, density, crystallinity, and coercive field (Hc) of Kuamet 6B2 specimens. LPBF is performed using pulsed laser emission with two laser power levels (120 W and 160 W), two scan speeds (615 mm/s and 888 mm/s), and time delays ranging from 1 to 300 ms. Introducing time delays as short as 50 ms significantly increases the amorphous fraction (AM%) without compromising density and leads to notable decreases in Hc. Multiphysics finite element (FEM) simulations reveal that this increase in AM% results from reduced devitrification in the heat-affected zone, as amorphous regions solidified during the previous track are allowed to cool during tOFF—an effect that becomes more pronounced with longer delays. This study demonstrates, for the first time, that implementing time delays can effectively resolve the "density/amorphous fraction" paradox in Fe-based MGs, providing a viable strategy for LPBF manufacturing of these alloys for soft magnetic applications.