Platinum Diffusion and Microstructure Change in a Single Crystal Superalloy and Nickel-based Model Alloys at 1000°C

Single crystal superalloy TMS82+ and model alloys of Ni-12Al and Ni-6Cr-8Co-12Al were electroplated with 5-6 mu m of platinum and heat treated at 1000 degrees C 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 gamma' phase. In TMS82+ superalloy inward diffusion of platinum resulted in loss of the gamma/gamma' microstructure and formation of new gamma and gamma' grains. The initial dissolution of the gamma' 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 gamma' layer being formed, however topologically close-packed (TCP) phase formation was not observed.