Ratchet Increasing Temperature Induced Stiffening and Intra-column Fracture of PS-PVD TBCs

Plasma spray-physical vapor deposition (PS-PVD) can prepare unique columnar thermal barrier coatings with both high thermal insulation and long lifetime. However, under solid dust erosion in aeroengines, delamination failure often occurs within the column bottom at 30 ~ 70 μm away from the interface rather than at the heterogeneous top coat/bond coat (TC/BC) interface. To elucidate the fracture mechanism, the in-situ deposit surface temperature evolution was investigated together with mechanical properties based on heat transfer model and experiments. The results show that the in-situ deposit surface temperature experiences ratchet increasing behavior, i.e., periodic increase and decrease, because of repeated scanning. Moreover, the overall rising trend of the in-situ deposit surface temperature due to thermal accumulation gradually slows with increasing scanning passes. Consequently, the mechanical properties of the coating, including hardness and Young’s modulus, increase along the growth direction following a similar trend of the overall change in the in-situ deposit surface temperature. In addition, stress simulation suggests that a stress concentration region appears at the column bottom, and the region of maximum stress is well consistent with the fracture at 30 - 70 μm from the TC/BC interface. This provides theoretical guidance to improve the erosion resistance of the PS-PVD coating by suppressing near-interface fracture.