Effect of high temperature oxidation on the surface state of FGH96 superalloy powders

The effect of high temperature oxidation on the surface state of FGH96 superalloy powders was studied by simulating the high temperature heating process during hot isostatic pressing (HIP) consolidation. The results indicate that the surface morphology, surface element distribution, and precipitate composition of the FGH96 superalloy powders are significantly changed by high temperature oxidation at near HIP temperature. With the increase of heating temperature and the extension of holding time, the surface solidification structure of cell crystals and dendritic crystals are covered by oxide/carbide layers. The high temperature oxidation process promotes the diffusion of Ni, Ti, Zr, Nb, Al, and C atoms inside the powder matrix to the powder surface. The pre-existing oxides (ZrO₂) on the powder surface provide the structural conditions for the nucleation of MC carbides (Ti, Nb)C. Controlling the formation of oxides on the powder surface can effectively limit the formation of prior particle boundaries (PPBs) defects in the alloys.