Design, fabrication and characterization of Fe-based bulk metallic glass composites by additive manufacturing

Abstract

Bulk Metallic Glasses (BMGs) possess unique properties such as high strength, large elastic limits, excellent magnetic behavior, and corrosion resistance, primarily due to their disordered atomic structure. However, their limited ductility at room temperature, caused by nonhomogeneous deformation, restricts widespread use. To overcome this, Bulk Metallic Glass Composites (BMGCs), which incorporate a ductile second phase into a glassy matrix, offer enhanced ductility while retaining strength. Among BMGs, Fe-based alloys are particularly attractive due to their favorable magnetic, mechanical, and corrosion-resistant properties and low cost. Yet, their poor glass-forming ability (GFA) and need for rapid cooling rates limit practical applications and component size and geometry. This study explores the feasibility of using Laser Powder Bed Fusion (LPBF), an additive manufacturing method offering high cooling rates (103-106 K/s), to fabricate Fe-based BMGCs in the Fe-Mo-P-C-B system. Six alloy compositions were designed through theoretical modeling and synthesized via arc melting. The most promising alloys, selected through microstructural and mechanical evaluation, were scaled up using Vacuum Induction Melting (VIM) and then gas atomized to produce powders suitable for LPBF. The atomized powders were processed by LPBF under various parameters to produce dense samples with retained glassy phase. While process optimization reduced defects (cracks and pores down to 1%) and achieved glassy phase fractions up to 24%, these conditions were not simultaneously met. The microstructure included ultrafine bcc Fe-Mo-C grains in the melt pool and mixed crystalline phases in the heat-affected zone. Compression tests showed no plastic deformation, but the LPBF samples demonstrated excellent wear resistance, combining low coefficients of friction and wear rates. Overall, the study reveals the trade-off between high density and glass formation in LPBF-fabricated Fe-based BMGCs, highlighting both the potential and the challenges of using additive manufacturing for producing such advanced materials.