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. Firstly, mechanism responsible for the multiple connections was revealed. 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. 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. Secondly, sintering-resistant TBCs were obtained by tailoring the width of interlamellar pores to avoid multiple connections. Composite TBCs were prepared to form wide interlamellar pores in the coatings. The increases in thermal conductivity and elastic modulus can be prevented to a large extent. Finally, TBCs with different contents of sintering-resistant pores were prepared. The thermal-insulation performance was found to be positively correlated with the contents of sintering-resistant pores. However, in thermal cyclic tests, the lifespan increased as the pore content increased from 0 vol.% to 20 vol.% but drastically decreased as the pore content increased further above 20 vol.%. A matching design on the sintering-resistant coatings were achieved to co-enhance the thermal insulation and thermal cycling span by 50% and 40%, respectively, from those of conventional TBCs. Therefore, the sintering-resistant structure is expected to considerably contribute to next-generation applications of TBCs.
 

thermal barrier coatings, sintering, failure mechanism, sintering-resistant design, long lifetime