Oxidation Behaviors of the NiCrAlY Bond Coats in the Thermal Barrier Coatings under External Loads

To understand the oxidation behaviors of the NiCrAlY bond coats in the thermal barrier coatings (TBCs) under external loads, uniaxial tensile and compressive experiments of the TBCs in air at 900 degrees C for 100 h were investigated. Then, the experimental results were explained by first-principles simulation. The results showed that the oxidation rate of the NiCrAlY bond coat was accelerated by external stresses. A 0.9 mu m thickness, a thermally grown oxide (TGO) layer was found in the NiCrAlY bond coat without stress after oxidation, while a 1.2 mu m thickness TGO layer was obtained in the NiCrAlY bond coat under tensile stress after oxidation. The main composition of the TGO layer was Al2O3 because Al was more easily oxidized without stress and under tensile stress. The thickest TGO layer with a thickness of 1.5 mu m was formed in the NiCrAlY bond coat under compressive stress after oxidation, consisting of the oxide of Al, Ni, and Cr. The first-principles results showed that the oxidation of Ni and Cr under compressive stress was easier than that under tensile stress due to the role of the 3d orbital.