Defect suppression via nano-Mo substitution during laser powder bed fusion of Mo alloys

• A partial metallic nanoparticle substitution strategy, rather than ceramic reinforcement, is proposed to enhance the L-PBF processability of Mo alloys without altering the alloy composition or introducing interfacial compatibility issues. • Single-track experiments and simulation analysis reveal that nanoparticle-substituted MoTi mixed powders exhibit broader processing windows and a larger melt pool area. • Dense, crack-free Mo alloys are observed with uniformly dispersed nanoscale TiO precipitates are obtained, which suppress the formation of Mo oxides. • This metallic nanoparticle substitution strategy provides an effective route to simultaneously mitigate lack-of-fusion defects and cracking in additively manufactured Mo alloys. Eliminating insufficient melting while avoiding keyhole defects is a critical challenge in the fabrication of refractory Mo-based alloys using laser powder bed fusion (L-PBF). Previous studies have primarily focused on ceramic nanoparticle reinforcement to improve the printability of Mo-based alloys. However, these strategies can introduce interfacial incompatibility and compositional heterogeneity. In this paper, a partial metallic nanoparticle substitution strategy is proposed to enhance the powder properties and L-PBF processability of challenging elemental MoTi mixed-powder systems. Single-track experiments and simulations revealed that the introduction of Mo nanoparticles enhanced the laser–powder interaction and thermal conductivity, leading to complete melting. Consequently, a fully dense MoTi alloy free from lack-of-fusion defects was successfully fabricated using L-PBF. This unique alloy exhibited a refined microstructure characterized by uniformly dispersed nanoscale TiO precipitates rather than the commonly formed Mo oxides, leading to reduced crack density. These findings demonstrate that the partial nanoparticle substitution strategy not only addresses the insufficient melting problem of refractory materials but also provides a promising pathway for the in situ removal of brittle boundary oxides, thereby contributing to crack suppression in the additive manufacturing of Mo-based alloys.