Spray power-governed microstructure and composition, and their effects on properties of lanthanum-cerium-tantalum-oxide thermal barrier coating

Lanthanum-cerium-tantalum-oxide (LCT) thermal barrier coatings (TBCs) were prepared by air plasma spraying at three different spray powers. Then, the effects of spray power on the microstructure, composition, thermo-physical properties, mechanical performances, and thermal cycling behaviors of the coatings were investigated in detail. The results indicated that when the spray power was increased from 30 kW to 42 kW in 6 kW steps, the coating became denser, the La/(Ce + Ta) ratio of the as-sprayed coating first increased slowly and then sharply, and the thermal conductivity and thermal expansion coefficient of the coating gradually increased and decreased, respectively. In addition, the Vickers hardness, Young's modulus, and fracture toughness of the coating first increased and then decreased. The spray power had a significant impact on the thermal cycling performance of LCT coating. The LCT coating prepared at low power showed better thermal shock resistance. The thermal expansion mismatch stress and the low fracture toughness of a ceramic top coat are the main reasons for the premature failure of the TBCs.