Tailoring sintering-resistant thermal barrier coatings by considering critical healing width of two-dimensional interlamellar pores

Large degradation in thermal insulation and strain tolerance is a main headache and a primary cause of the failure for plasma-sprayed thermal barrier coatings (TBCs) during service. One mechanism behind such degradation is the healing of interlamellar pores formed by multiple connections between edges of a pore, which significantly speeds up healing during thermal exposure. The objective of this study is to obtain sintering-resistant TBCs by tailoring the width of interlamellar pores to avoid multiple connections. Firstly, the mechanism responsible for the multiple connections was revealed. The splat surfaces before and after thermal treatments were characterized via an atomic force microscope (AFM). The roughening of the pore surface occurs during thermal exposure, along with the grain growth inside the splats. Consequently, the local surface height increases, which causes multiple connections and healing of the interlamellar pores. Secondly, critical widths of the interlamellar pores for avoiding the multiple connections during thermal exposure are established by correlating the extent of surface roughening with the growth of individual grains. The height increase of the splat surface and the growth of the grain size (D) were found to increase with the exposure temperature and duration. A relationship linking the height increase and the growth of the grain size induced by thermal exposure in plasma-sprayed ceramic splats was obtained. Finally, composite TBCs were prepared to form wide interlamellar pores in the coatings. Using this design, the increases in the thermal conductivity (λ) and the elastic modulus (E) can be prevented to a large extent. Thus, sintering-resistant TBCs that maintain high thermal insulation and strain tolerance, even after long thermal exposure, can be created.