Microstructure and Nanoindentation Evolution of (Ni,Pt)Al Coating on IC21 Substrate at 1100 °C

In this study, a ~20 μm (Ni,Pt)Al coating was applied to an IC21 substrate via electroplating followed by aluminizing. A thermal exposure test at 1100 °C in air was used to investigate the microstructure evolution and nanoindentation behavior of samples with and without coating. The experimental results show that the (Ni,Pt)Al coating caused a phase change from β-(Ni,Pt)Al to Ni3Al, and the Topologically Close-Packed (TCP) phase at the interdiffusion zone grew larger after thermal exposure for 200 h at 1100 °C, while a layer of γ’ phase was formed on the surface of the IC21 substrate. The nanoindentation test indicated that the elastic modulus was reduced in both annealed samples (with and without coating), and after annealing the sample with coating had higher elastic modulus than the sample without coating. This result reveals that the coating effectively prevented the precipitation of refractory metal elements and the coarsening of the microstructure in the substrate, and thus shows that the coating had advantages not only in terms of improving the high-temperature oxidation properties of the substrate, but also played a significant role in improving the mechanical properties of the substrate.