Surface Segregation and Oxidation Behavior of Superalloy Powders Fabricated by Argon Atomization

Abstract

Particle surface component and valence state of nickel-based superalloy FGH96 powders fabricated by argon gas atomization have been measured by X-ray phoelectron spectrometer (XPS) to recognize the effect of powder size, surface segregation and heat treating on the oxidation behavior of powders. Type and phase structure of prior particle boundaries (PPBs) precipitated in HIPed superalloy have been studied also. The results showed that prior particle surface segregation and oxidation happened during the powder collection and storage with the C, O, Ti elements enrichment and Ti, Cr, Al, Zr elements oxidation in the surface respectively. During the heat treating of 1150/2h, normal segregation element Ti and Zr enriched more apparently in the particle surface, on the contrary, negative segregation elements Ni, Al and Co diffused into the particle inner. Furthermore, the higher oxygen level on particle surface enhanced to form much more oxides such as ZrO2, TiO2and Cr2O3. During HIP process of 1150/2h/150MPa, the oxide ZrO2as the nuclei accelerated the preferential precipitation of MC-type carbides which forms the continuous harmful PPBs. Definitely, PPB precipitation depended on the prior particle surface segregation and oxidation, surface elements Ti, Cr and Nb enrichment and oxidation reaction enhancement in high temperature such as 1150. Small powders always had little segregation in the surface and thin oxidation layer, but had more oxygen content per weight for its higher specific surface. So using some powders with optimum particle size and lower oxygen content can help to reduce the PPB precipitation.