Abstract
In order to make the test standard for thermal shock resistance of ceramic coatings, both fracture mechanisms of the coating and main factors for the fracture have to be clarified. In this study, cyclic thermal shock testings were carried out on the ZrO2/NiCrAlY plasma sprayed coatings, and unsteady thermal stress analyses by FEM were also conducted on these testings. The results obtained are summarized as follows.(1) ZrO2 coatings were suddenly spalled off completely during or just after the cooling process, after some cycles of thermal shock.(2) Fracture took place at the interface of ZrO2 sprayed particles about 10μm away from the ZrO2/NiCrAlY interface.(3) From the results of unsteady FEM analyses, large compressive stress was recognized in the ZrO2 coating during the cooling process.(4) From the results of both SEM observations and FEM analyses, it was revealed that the fracture of the coating was caused by unstable propagation of internal crack which was generated at the inside of the coating layer near the ZrO2/NiCrAIY interface.
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