Platinum Diffusion and Microstructure Change in a Single Crystal Superalloy and Nickel-Based Model Alloys at 1000ºC

Single crystal superalloy TMS82+ and model alloys of Ni-12Al and Ni-6Cr-8Co-12Al were electroplated with 5-6μm of platinum and heat treated at 1000ºC for up to 100hrs. In the model alloys the platinum concentration gradient in the interdiffusion region caused uphill diffusion of aluminium. The subsequent surface enrichment led to formation of aluminium-rich γ′ phase. In TMS82+ superalloy inward diffusion of platinum resulted in loss of the γ/γ′ microstructure and formation of new γ and γ′ grains. The initial dissolution of the γ′ cubes was due to the outward diffusion of aluminium. Again, the presence of a platinum gradient in the interdiffusion region resulted in uphill diffusion of aluminium and a net increase in aluminium content at the alloy surface, leading to a near-surface single-phase γ′ layer being formed, however topologically close-packed (TCP) phase formation was not observed.