Optimizing process strategies in laser powder bed fusion to reduce crack formation in Fe-based bulk metallic glasses

Bulk metallic glasses (BMGs) are known for their exceptional mechanical and electrochemical properties, including high strength, excellent corrosion resistance, and catalytic activity. However, their large-scale application remains limited due to size restrictions in conventional casting, as high cooling rates are required to achieve amorphous solidification. Laser Powder Bed Fusion of Metals (PBF-LB/M) offers a promising alternative, as its high cooling rates and small melt pool volumes can overcome these limitations and enable the fabrication of larger amorphous parts. Among BMGs processed via PBF-LB/M, Zr-based alloys are most common due to their good glass-forming ability (GFA) and processability. However, their high sensitivity to oxygen contamination significantly reduces their GFA, necessitating high-purity feedstock and increasing material costs. In contrast, Fe-based BMGs are less sensitive to oxygen and offer a cost-effective alternative, combining good mechanical properties, corrosion resistance, and catalytic performance. Yet, their processing via PBF-LB/M is challenging due to a strong tendency for crack formation caused by residual stress. This work addresses the processing of a Fe-based BMG using PBF-LB/M and investigates strategies to reduce cracking, both in bulk material and in thin features such as struts, which are particularly relevant for complex, filigree structures, desirable for PBF-LB/M parts. By optimizing key process parameters, such as scan speed, laser power and inter-vector times, as well as process conditions including platform preheating and tailored scan strategies, heat accumulation can be reduced. This results in a lower degree of crystallinity and reduced residual stress, thereby decreasing crack formation and significantly improving printability. To evaluate the thermal and microstructural effects of different processing conditions, differential scanning calorimetry (DSC), metallographic cross-sections, and optical microscopy were employed.