Periodic Cracking of Thermal Barrier Coatings for Improved Interfactial Thermal Fracture Resistanace: Experiments and Analysis

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9908187KokiniCeramic thermal barrier coatings offer the potential for improved efficiency, fuel economy, durability and performance in high temperature applications such as aerospace and aircraft engines, gas turbines and diesel engines. In these applications, the coatings are subjected to varying high temperatures and temperature gradients, which can ultimately result in delamination and spalling of the coating. The presence of surface cracks in the coating has been shown to increase its life. Furthermore, recent experimental and analytical results have shown that changing the periodicity and length/thickness ratio of such cracks can decrease interfacial crack propagation in thick coatings which are subjected to high surface temperatures and large temperature gradients. These results suggest that by introducing a periodic crack system during manufacture it should be possible to reduce interface cracking in service. This opens up the possibility of using thick thermal barrier coatings produced by plasma spraying, which would provide significantly greater thermal protection and longer life under thermal loads and also give greater design flexibility and reduced cost of processing. Thus, the objectives of the proposed research are: (a) to develop an understanding of the response of interface cracks in thermal barrier coatings subjected to high heat fluxes in the presence of surface cracks introduced during the thermal spray process; (b) to use controlled experiments and analytical models to determine the effects of crack length, periodicity, thickness, combined with time-dependent material behavior of the coating under different thermal boundary conditions on the thermal fracture of the interface.***