Architecture of functionally graded ceramic coatings against surface fracture

An analytical study was performed to study the effect of architecture on the initiation of surface cracking in multilayer ceramic coatings. Two modes of crack initiation were considered: 1) tension resulting from stress relaxation, and 2) cyclic thermal fatigue. Transient temperature distributions were determined using a finite difference technique, and stress distributions were calculated using a multilayer beam theory. The results showed that as more layers were added and as the ceramic coating became thinner, lower maximum surface stresses resulted during cooling after stress relaxation. Also, a thick eight layer coating had similar thermal fatigue behavior to a thin single layer coating. It was determined that a thick multilayer coating adds a significant amount of thermal protection when compared to a thin single layered coating.