Effects of laser energy density on melting mode, microstructure, and anisotropy of mechanical properties of Ni-Cr-Fe-based superalloy fabricated by LPBF

Ni-Cr-Fe-based superalloy samples were fabricated by laser powder bed fusion (LPBF) under three representative melting modes governed by different laser energy densities. The effects of melting mode on molten pool thermodynamics, microstructural evolution, and mechanical properties were systematically investigated. Among the three modes, the shallow keyhole mode achieved the best overall forming quality and mechanical performance, exhibiting the lowest surface roughness (Sa = 8.183 μm) and porosity (0.41%). Marked anisotropy in microstructure and mechanical behavior was observed. The horizontal (XOY) plane was characterized by equiaxed grains and dense cellular structures, whereas the vertical (XOZ) plane consisted predominantly of coarse columnar grains. Accordingly, the XOY plane exhibited higher hardness, yield strength, and ultimate tensile strength, while the XOZ plane showed better elongation. To further reveal the underlying mechanisms, computational fluid dynamics (CFD) simulations were performed to analyze the temperature field and melt flow behavior under different melting modes. Based on the simulation results, a criterion for melting mode identification was proposed. The superior yield strength of the XOY plane was mainly attributed to its higher initial dislocation density and greater density of fine cellular boundaries.