Surface thermal fracture of functionally graded ceramic coatings: Effect of architecture and materials

Abstract

An analytical study was performed in order to investigate the effect of architecture and material properties on the initiation of surface cracking in functionally graded ceramic coatings. The mode of crack initiation considered was tension resulting from stress relaxation. The thermal stress distributions were calculated using a multilayer beam theory. The results obtained showed that the functional grading of the coating, as well as decreasing its thermal expansion coefficient and modulus of elasticity, decreases the transient surface stresses during cooling after stress relaxation. Changing the thermal expansion coefficient and modulus of elasticity of the substrate has a small effect on the surface stresses.