Effects of volumetric energy density on melting modes, printability, microstructures, and mechanical properties of laser powder bed fusion (L-PBF) printed pure nickel

Abstract

Volumetric energy density (VED) is a fundamental criterion for the laser powder bed fusion (L-PBF) process, influencing various forming characteristics. This study employed L-PBF to print pure nickel (Ni) using different VEDs across various melting modes. The thermodynamics in the different melt pools, obtained microstructural features, and tensile properties were characterized and investigated. The results reveal a higher likelihood of keyhole mode melt pool formation than the conduction mode due to the peak temperature exceeding 3005 K. The larger size and slower cooling rate of the keyhole mode melt pool facilitate the formation of cellular subgrains in the central zone and the overall grain coarsening. Compared to the conduction mode, the microstructure in the keyhole mode exhibits a higher dislocation density and a distinct distribution pattern for each type of dislocation. Unlike the L-PBF of commercial Ni alloys, where alloy element distribution significantly impacts tensile performance, the tensile performance of L-PBF Ni is governed by the interaction between grain morphology, dislocation density and distribution.