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 primary cause of 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 the edges of a pore, which significantly speeds up the 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, mechanism responsible for the multiple connections was revealed. The splat surface before and after thermal treatments were characterized via atomic force microscopy. The roughening of the pore surface occurs during thermal exposure, along with grain growth inside the splats. Consequently, local surface height increases, which causes multiple connections and healing of interlamellar pores. Secondly, critical widths of interlamellar pores to avoid multiple connections during thermal exposure is established by correlating the extent of surface roughening with the growth of individual grains. The height increase of the splat surface and growth of grain size were found to increase with the exposure temperature and duration. A relationship linking height increase and grain size growth 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, increases in thermal conductivity and elastic modulus can be prevented to a large extent. Thus, sintering-resistant TBCs that maintain a high thermal insulation and strain tolerance, even after long thermal exposure, can be created.