A bimodal-structured coating with columnar/lamellar trans-scale features for strain-tolerant and thermal insulative performances

Long lifespan is a basic support for thermal insulation function of thermal barrier coatings (TBCs). However, it is difficult to simultaneously achieve these two performances in conventional lamellar or columnar TBCs, which often have to sacrifice one performance due to the limitation of the mono-featured structure. In this work, a bimodal-structured coating with columnar/lamellar trans-scale features was designed to meet multiple requirements. The micro-lamellar structure was deposited to effectively prevent heat flux, and the macro-columnar structure was tailored to tolerate strain. Firstly, a method to prepare and tailor the bimodal-structured coating was proposed. From the view of thermal insulation, thermal conductivity of the bimodal-structured coating was comparable to the typical lamellar structure, which is only about 60 % of the typical columnar structure. From the view of durability, thermal cyclic lifespan of the bimodal-structured coating can be extended by 3–7 times compared to the typical lamellar structure. Secondly, the substrate constraint-related mechanism responsible for the failure of lamellar structure is investigated. A decrease in strain tolerance (ST) of 40 %–80 % was observed due to exposure to high temperatures. Additionally, the sintering-induced healing of the two-dimensional (2D) pores was found to be correlated with changes in the mechanical properties of the coatings, and this was found to be a primary cause for the decrease in ST. Finally, the macro-columnar structures were optimized based on tailoring the distance between neighboring vertical cracks, L, and coating thickness, h, and a finite element model was developed to investigate the optimization of the geometry of such coatings. The critical value for L/h is found to be approximately 10; below this value, the crack driving force was seen to be significantly reduced. Overall, the bimodal-structured coating is expected to co-enhance thermal insulation and thermal cyclic performances, which represents a fundamental step toward the development of advanced TBCs for future applications.