Effects of laser surface melting on the high temperature oxidation behaviour of Inconel 625

This paper investigates the microstructure and high-temperature oxidation characteristics of laser-remelted IN625. A 400 W continuous laser was used for laser surface remelting at different scanning speeds. Isothermal oxidation experiments were conducted in air at 900°C for 2, 10, 25, 50, and 100 hours. The evolution of the microstructure was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron backscattering diffraction (EBSD). The results show that after laser surface remelting, the large Nb-rich precipitates were refined and uniformly distributed in the γ-matrix. A mixed oxide composed of Cr2O3 and (Ni, Fe)Cr2O4 spinel oxides was formed in the as-cast IN625, while a dense Cr2O3 oxide layer was formed in the laser-remelted IN625. The study found that semi-continuous Nb2O5 bands formed in the laser-remelted IN625 after oxidation. Further research indicates that grain growth occurred after laser surface remelting, forming a coarse-grained region near the surface. The coarse grains restrict grain boundary diffusion, thus a corresponding reduction in oxide layer thickness is observed in IN625 that has undergone laser surface remelting.