Sintering induced the failure behavior of dense vertically crack and lamellar structured TBCs with equivalent thermal insulation performance

Both thermal cyclic lifetime and thermal barrier performance are essentially important to the application of thermal barrier coatings (TBCs). In this study, equivalent thermal insulation conception is introduced to the design of TBCs to fairly compare different structured TBCs. Dense vertically crack (DVC) structured TBCs and the lamellar structured TBCs with same top coat thickness of 1000 µm (D1000 and L1000), and lamellar structured TBCs with 570 µm (L570, equivalent thermal insulation performance with D1000) top coat were prepared. Their lifetimes were evaluated under gradient thermal cyclic test. D1000 TBC shows a rather longer lifetime than L1000 TBC because of the alleviation of vertically cracks, but D1000 TBC possesses a much lower thermal barrier performance than L1000 TBC due to the dense structure of D1000 TBC. However, for the TBCs with the same equivalent thermal insulation performance, L570 TBC presents a more than two times longer lifetime than D1000 TBC. TGO thickening and phase transformation were proved not responsible for the failure of L1000 and D1000 TBCs in the present condition. The in-plane elastic modulus and Vickers hardness across top coat thickness were examined, and the results proved that the mechanical evolution of the top coat after high temperature exposure resulting in the competition between driving force and cracking resistance dominates the failure behavior of TBCs. This study is beneficial for the comprehensively understanding of the failure behavior of DVC and lamellar structured TBCs, and thereby shed light to further coating structure optimization and design innovation.