Effect of Y2O3 Content on the Microstructure and Thermal Shock Resistance of Al2O3–Y2O3 Composite Coatings

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Abstract
Thermal shock resistance is a critical parameter for evaluating the long-term service reliability of protective coatings in high-temperature molten-salt environments. In this study, Al2O3–Y2O3 composite coatings containing 0, 2, 5, and 8 wt.% Y2O3 were fabricated on 316L stainless-steel substrates by atmospheric plasma spraying (APS). Their phase constitution, microstructure, mechanical properties, and thermal shock resistance were systematically investigated. The results showed that, with increasing Y2O3 content, the relative content of α-Al2O3 gradually increased, whereas the coating densification, microhardness, and fracture toughness first increased and then decreased. After 200 thermal shock cycles, the thermal shock resistance of the Al2O3–Y2O3 composite coatings followed the order of 5 wt.% Y2O3 > 2 wt.% Y2O3 > 8 wt.% Y2O3 > 0 wt.% Y2O3, indicating that the addition of an appropriate amount of Y2O3 significantly improves the thermal shock resistance of the coatings. Analysis of the failure mechanism further revealed that the addition of an appropriate amount of Y2O3 enhanced phase stability and optimized the coating microstructure, thereby improving the crack-propagation resistance and ultimately enhancing the thermal shock resistance. In contrast, excessive Y2O3 weakens this beneficial effect because of increased microstructural heterogeneity and a higher defect density.
Funding Information
  • Fourth Batch of Gansu Provincial Outstanding Leading Talent Fund Project (ZZ2023G50100013)
  • Gansu Provincial Major R&D Program (24ZDWA008)
  • Gansu Provincial Higher Education Faculty Innovation Fund Project (2026B-454)
  • Doctoral Scientific Research Foundation of Hubei University of Automotive Technology (BK202468)
  • National Natural Science Foundation of China (52462010)
  • Gansu Academy of Sciences (25JRRA055)

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