Thermal cycling behavior of La2Zr2O7 thermal barrier coatings by plasma spraying of an amorphous and crystalline precursors

Abstract

Single layer thermal barrier coatings (TBCs) of La2Zr2O7 (LZ) and double layer YSZ/LZ TBCs produced from amorphous (LZA) and crystalline (LZC) feedstock were deposited by atmospheric plasma spray (APS) technique. Thermal cycling behaviors, phase structures and cross-sectional morphologies before and after thermal cycling tests of these coatings were studied in detail. Microstructural properties of three different types of coatings affect thermal cycling lifetime of the coatings. The thermal cyclic test results indicate that the thermal cycling lifetime of LZC/YSZ double layer TBCs is longer than that of single layer LZA and LZC TBCs due to the fact that there are improvements in the sintering resistance ability, thermal expansion mismatch between the ceramic layer and the metallic substrate at high temperature, and thermal insulation effect of DLC (double layer coating) LZ/8YSZ TBCs. The thermal cycling tests indicated that the YSZ/LZC coating has a lifetime of 400 cycles which is longer than single layer LZA and LZC coating. The failure of LZC and LZA coatings mainly results from excessive growth of thermally grown oxide layer, the thermal expansion mismatch between ceramic top coatings and bond coat and thermal stresses accumulated during thermal cycling tests.