Influence of Build Orientation and Heat Treatment on Mechanical, Tribological, and Corrosion Performance of LPBF Inconel 625

This study examines the influence of build orientation and post-processing heat treatments on the microstructure and properties of laser powder bed fused (LPBF) Inconel 625 (IN625), with conventionally manufactured material used as a reference. The as-built alloy exhibits a highly anisotropic microstructure composed of elongated columnar grains, a fine cellular/dendritic substructure, and high dislocation density. Vertically built specimens show greater columnar continuity than horizontally built ones, resulting in pronounced mechanical anisotropy. Stress-relief annealing at 870 °C reduces residual stresses through recovery, while preserving the solidification microstructure without recrystallisation. Solution annealing at 1050 °C promotes microstructural homogenisation by dissolving segregation-related phases and partial recrystallisation. Recrystallisation is orientation-dependent and more extensive in horizontally built specimens, leading to lower dislocation density and a more equiaxed grain structure, while vertically built material retains elements of the columnar architecture. These microstructural changes directly affect performance. Horizontally built specimens exhibit higher yield and tensile strengths, whereas vertically built specimens show superior ductility and impact toughness. Corrosion resistance improves progressively with heat-treatment temperature, with solution annealing achieving near-conventional performance due to enhanced chemical homogeneity. Although the as-built condition shows higher strength and hardness, it suffers from increased wear associated with brittle behaviour; heat treatments reduce wear anisotropy, with solution annealing providing the highest wear resistance. LPBF IN625 responds non-uniformly to conventional heat treatments, and build orientation plays a critical role in controlling recrystallisation kinetics and property anisotropy, providing guidance for optimised post-processing strategies.