Laser beam surface modification of additively manufactured Ni-based superalloy: Correlations of microstructure and tribological/corrosion properties

A Ni-based superalloy (with reduced Ni, Cr, and Nb contents compared to Inconel 718) was fabricated via Laser Powder Bed Fusion (LPBF) and subsequently laser surface-modified. Characterization included optical and scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe microanalysis (EPMA), electron backscatter diffraction (EBSD), nanoindentation, reverse potentiodynamic polarization, and sliding wear testing in a highly ionic electrolyte. The as-built alloy (2.2% porosity) exhibited a fine cellular “fish-scale” structure free of Laves phases. Laser processing (400 W, 5 mm/s, optimized via computer simulation) melted the surface to a depth of 600-650 μm depth, forming a porosity-free zone with coarse columnar grains and a polyhedral transition zone. The modified layer contained (Ti,Al) oxides, (Ti,Nb)N, a near-continuous intergranular network of eutectic Laves phase (Ni,Fe,Cr) 2 (Nb,Ti,Si,Mo), along with silicides MSi 2 (M: Nb,Cr,Fe), (Nb,Ti)C, Cr 7 C 3 , and TiO 2 . Laser modification reduced hardness from 4.3 GPa to 3.3 GPa due to microstructural coarsening. Despite this hardness reduction, the wear performance was maintained due to densification, lubricating oxides, and hard intermetallic phases. However, resistance to localized and general corrosion deteriorated due to microstructural coarsening and secondary phases that disrupted the passive film or acted as cathodic sites.