Properties evaluation and failure behaviour of plasma sprayed Y4Hf3O12 for thermal barrier coating applications

In this study, thermal barrier coating (TBC) of Y4Hf3O12 compound was produced by the plasma spray method. Phase composition, microstructure, thermophysical properties, high temperature stability, as well as CaO-MgO-Al2O3-SiO2 (CMAS) corrosion behaviour were investigated for Y4Hf3O12 coating. Results reveal Y4Hf3O12 coating of defective fluorite structure, as a result of high concentration of Y cation, to exhibit low thermal conductivity, outstanding structure stability up to 1300 degrees C and super good protectiveness against CMAS, but with relative low TEC. Preliminary findings support that Y4Hf3O12 ceramic can be top-layer materials on YSZ to form a double-ceramic-layer (DCL) TBC system. Thus, by adding a YSZ buffer layer, the Y4Hf3O12/YSZ DCL TBC was further developed on Ni-based superalloy and its thermal cycling durability was evaluated. It indicates that this DCL TBC system could undertake a cyclic lifetime longest to similar to 459 cycles. The failure behaviour in thermal shock test is related to the crack evolution induced by a combination of TEC mismatch, TGO growth and sintering of top-layer Y4Hf3O12.