Thermal cycling behaviors of thermal barrier coatings on intermetallic Ni₃Al based superalloy

Ni₃Al based alloy IC6, a high performance cast alloy with approximately 14 wt.% Mo addition, has been developed for turbine blades and vanes of advanced aero-engines and other high temperature structural components. However, because of the high Mo content, during high temperature use, Mo will diffuse into the protective coating layer, which will affect the thermal cycling performance directly. In order to block the diffusion and improve the thermal cycling behavior of thermal barrier coatings (TBCs), a Si chemical gradient MCrAlY-Si bond coat was prepared by changing the Si content from 0.35 wt.% at the interface of substrate and bond coat to almost 0 near to the surface of the bond coat. For comparison, conventional two-layered structural TBCs with MCrAlY as bond coat were also prepared. The fabricated coatings were evaluated for the microstructures and the composition distribution properties, such as thermal stability and resistance to oxidation. For the bond coat without Si addition, Mo content near the surface was higher than 7 wt.% after isothermal oxidation at 1373 K for 60 h and 12.5 wt.% after thermal cycling tested at 1373 K for 300 h (600 cycles). However, in the Si chemical gradient bond coat, only 0.4 wt.% Mo was detectable after isothermal oxidation at 1373 K for 100 h and approximately 0.66 wt.% after thermal cycling tested at 1373 K for 340 h (680 cycles).