Enhanced densification of copper during laser powder bed fusion through powder surface alloying

In this study, a novel approach of powder surface alloying is proposed to address the issue of insufficient densification of printed copper (Cu) from high laser-absorbing Ni coated Cu powder through laser powder bed fusion. Three types of powder consisting of original Ni-coated powder (surface adhesion), partially Ni-diffused powder (partial surface alloying) and surface Ni-alloyed powder (complete surface alloying) were adopted to validate the effectiveness of the approach. All these powders significantly decreased the high laser reflectivity of Cu powder. The surface Ni-alloyed powder successfully melted the Cu powder to eliminate the lack-of-fusion pores in the printed Cu samples such that best dimensional accuracy and highest relative density of up to 99.6% was obtained. The interface condition between outer Ni coating and Cu powder played an important role in the densification process. The solid solution Ni in the surface Ni-alloyed powder maximized the contact area, reduced the thermal resistance and enhanced heat transfer efficiency, which eventually promoted the melting of Cu powder and eliminated the lack-of-fusion pores. Ni content is also revealed as an important factor in balancing electrical conductivity and mechanical properties. The optimal Ni content has been determined as 0.4 wt% for powder with surface Ni-alloyed