Thermal fracture mechanisms in ceramic thermal barrier coatings

Ceramic thermal barrier coatings (TBCs) represent an attractive method of increasing the high-temperature limits for systems such as diesel engines, gas turbines, and aircraft engines, However, the dissimilarities between ceramics and metal, as well as the severe temperature gradients applied in such systems, cause thermal stresses that can lead to cracking and ultimately spalling of the coating, This paper reviews the research that has considered initiation of surface cracks, initiation of interfacial edge cracks, and the effect of a transient thermal load on interface cracks, The results of controlled experiments are presented together with analytical models, The implications of these findings to the differences between diesel engines and gas turbines are discussed, The importance of such work for determining the proper design criteria for TBCs is underlined.