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The microstructure of the ceramic topcoat has a great influence on the service performance of thermal barrier coatings (TBCs). In this study, conventional layered-structure TBCs, nanostructured TBCs, and novel-structured TBCs with a unique microstructure were fabricated by air plasma spraying. The relationship between the microstructure and properties of the three different TBCs was analysed. Their thermal insulation ability, sintering resistance, and durability were systematically evaluated. Additionally, their failure modes after being subjected to two kinds of thermal shock tests were analysed. The results revealed that the novel-structured TBCs had remarkably superior performances in all the examined aspects. The thermal conductivity of the novel-structured TBCs was significantly lower than those of the conventional and nanostructured TBCs both in the as-sprayed state and after thermal treatment for 500 h at 1100 °C. The macroscopic elastic modulus of the novel-structured TBCs after sintering at 1300 °C for 100 h was similar to those of the conventional and nanostructured TBCs in the as-sprayed state. During both a burner rig thermal shock test and a furnace cyclic oxidation test, the thermal shock lifetime of the novel-structured TBCs was much longer than those of the conventional and nanostructured TBCs. This study has demonstrated novel-structured plasma-sprayed TBCs with high thermal insulation ability and high durability.

The properties of coating materials can be improved via microstructural design. This study proposed a structure control strategy for plasma sprayed YSZ coatings. A non-conventional powder feeding method was used to controllably embed second-phase particles into a conventional coating matrix during plasma splaying, that is, two types of powder were fed at two specific locations into the plasma jet whereby producing a controlled composite thermal barrier coating (TBC) comprising a conventional coating matrix containing porous micro-agglomerated particles. Properties improvements can be attributed to this new structure. The thermal insulation ability, anti-sintering properties and thermal shock resistance of the novel TBC were superior to conventional TBCs. This structure control strategy provided a new approach to the design and development of advanced coatings and shows great promise for application in next generation thermal barrier coatings.