On damage process of ceramic thermal barrier coatings subjected to high-temperature tensile loading

Abstract

Thermal barrier coatings (TBCs) have been deposited onto the blade surface in a land-based gas turbine according to increase of turbine inlet temperature (TIT). In service of those gas turbines, it has been known that cracking and delamination in TBC is one of the serious damages. Thus, it is very important issue to assure the reliability for TBCs or advanced protective coatings in service. The aim of this study is to clarify how micro damage progresses in TBC and porous TBC, which is called P-TBC here, under a tensile loading at a high-temperature environment. Here, P-TBC has been developed by Arai in order to reduce thermal conductivity and infiltrate coolant gas for achieving transpiration cooling technology. As a result, the surface cracks propagated in a direction perpendicular to the interface in both TBC and P-TBC samples. When a tip of those cracks reached the interface, the crack was curved along the interface between substrate and bond coat in case of TBC sample at room temperature especially. On the other hand, the surface crack propagated along the interface between top and bond coats in case of P-TBC sample. In the tensile test conducted at 1273K, the crack path was located at the interface between top and bond coats in both TBC and P-TBC samples. The quantitative evaluation revealed that critical strain up to crack initiation was almost the same at TBC and P-TBC, and number of cracks per length in TBC sample was higher than that of P-TBC. The J-integral-based adhesive strength of TBC sample was stronger than that of P-TBC.