Thermal and mechanical properties of nano-YSZ–Alumina functionally graded coatings deposited by nano-agglomerated powder plasma spraying

Abstract YSZ, layered YSZ–Alumina and functionally graded YSZ–Alumina TBC coatings were deposited by atmospheric plasma spraying using nano-agglomerated powder. FE-SEM images of coatings showed formation of nanostructure. The thickness of TGO for layered YSZ–Alumina and FG YSZ–Alumina coatings was lower than that found in the case of YSZ coating. This demonstrates the beneficial effect of Alumina as a diffusion barrier for oxygen during high temperature exposure. In layered YSZ–Alumina coatings because of difference in thermal expansion coefficients of YSZ and Alumina and stresses developed at the interface, the tensile strength and thermal shock resistance are lower than FG coatings and Failure of coatings occurred at YSZ–Alumina interface. In FG coatings distribution of stresses in the graded layers provided higher tensile strength and thermal shock resistance and also higher resistance to spallation in oxidation test which is caused by TGO growth.