SURFACE THERMAL FRACTURE OF FUNCTIONALLY GRADED CERAMIC COATINGS - EFFECT OF ARCHITECTURE AND MATERIALS

An analytical study was performed in order to investigate the effect o f architecture and material properties on the initiation of surface cr acking in functionally graded ceramic coatings. The mode of crack init iation considered was tension resulting from stress relaxation. The th ermal stress distributions were calculated using a multilayer beam the ory. The results obtained showed that the functional grading of the co ating, as well as decreasing its thermal expansion coefficient and mod ulus of elasticity, decreases the transient surface stresses during co oling after stress relaxation. Changing the thermal expansion coeffici ent and modulus of elasticity of the substrate has a small effect on t he surface stresses.