Thick thermal barrier coatings with layer-graded bond coat systems were developed for diesel engine applications. In general, coating systems for diesel applications need to be designed to minimize thermal stresses at the component edge and corner regions while providing thermal insulation and oxidation resistance. The concept of low expansion and layer-graded bond coat systems was proposed because the novel coating systems can be easily tailored to meet the stringent performance requirements under severe cyclic loading during engine operation. In this study, thermal fatigue behavior of several coating systems was evaluated using burner rigs and high heat flux laser tests under thermal transients which simulate those in diesel engines. Thermomechanical fatigue tests were also carried out for the coating Systems under simultaneous thermal and mechanical fatigue conditions. Effects of the thermal-mechanical loading, interfacial temperature, and coating configuration on thermal barrier coating life were investigated. Experiments showed that the layer-graded bond coat system possesses lower interfacial stresses and excellent oxidation resistance as compared to conventional thick TBC coating systems, thus significantly improving the coating performance and durability.
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