Microstructural stability of a Ni–Pt–Al coating on CMSX-10 alloy at 950 and 1100°C

Abstract

Specimens of CMSX-10 alloy have been platinum aluminised to give a two phase PtAl2–(Ni, Pt)Al coating. Specimens of the coated alloy were exposed in an oxidising environment for 188, 350 and 750 hours at temperatures of 950 and 1100°C. At 950°C the two phase coating equilibrates with the substrate and this results in the development of a single phase (Ni, Pt)Al coating. After 750 hours, β–γ’ transformation effects are observed but there is significant Ta present in the γ’ grains. At 1100°C more rapid outward diffusion of nickel and countercurrent diffusion of aluminium facilitates more extensive β–γ’ transformation and Ta substituted γ’ grains are clearly visible after 188 hours. At both temperatures, refractory element rich phases form in a secondary equilibration zone adjacent to the substrate as a result of nickel depletion. The development of these phases at 1100°C is significant, such that they extend to a depth of 0.2mm beneath the diffusion layer