The Effect of Microstructure and Surface Finish on the High Temperature Oxidation of Laser Powder Bed Fused IN625

Abstract Isothermal oxidation of Laser Powder Bed-Fused (L-PBF) IN625 was investigated in air at 950 ℃ for 1000 h, across multiple heat-treated and surface conditions. Surface finish was the dominant factor influencing oxidation kinetics, with microstructure exerting a measurable secondary effect. Ground L-PBF IN625 exhibited oxidation behaviour comparable to wrought Ni-based superalloys, regardless of microstructural anisotropy. Additive surface roughness and Centrifugal High Energy Finished surfaces exhibited accelerated kinetics and a departure from sub-parabolic to cubic behaviour, showing spallation, severe void formation and intergranular oxidation. Segmented kinetic analysis revealed that additive surfaces exhibited an oxidation rate index ( n > 2) during early exposure, followed by a transition to slower growth. Mn-spinel was detected throughout the external scale, but its mechanistic contribution to this transition remains uncertain. Growth of the near-continuous Ni 3 (Nb, Mo) δ -phase varied by condition and is proposed to improve the adherence of chromia by increasing the critical temperature change for spallation. Graphical Abstract