Microstructure, thermophysical properties and thermal shock resistance of toughened hafnia-based thermal barrier coating fabricated by plasma spray

Abstract

Yttria fully stabilized cubic hafnia (YFSH) is a highly promising thermal barrier coating (TBC) material for high-temperature aero-engine applications owing to its high melting point and phase stability. However, its relatively low fracture toughness impedes its broader application. To overcome this limitation, a T’-YSZ@Al₂O₃ core-shell structured powder (with Al₂O₃ constituting 20 vol% of the YSZ) was introduced. Coatings designated as CSYSH24, comprising YSH24 (Hf_0.76Y_0.24O_1.88) toughened with 30 vol% T’-YSZ@Al₂O₃, were fabricated via atmospheric plasma spraying (APS). The phase composition, microstructure, mechanical properties, high-temperature phase stability, and thermal shock resistance at 1300 °C were systematically investigated. The results demonstrate that the CSYSH24 coating retains flattened T’-YSZ@Al₂O₃ core-shell particles, while the matrix preserves a single C phase. Notably, the fracture toughness of the CSYSH24 coating (2.00 MPa·m^1/2) is significantly enhanced compared to the baseline YSH24 coating (1.77 MPa·m^1/2). Moreover, the CSYSH24 coating exhibits exceptional phase stability, with no phase transformation observed after thermal aging at 1300 °C for 96 h. Crucially, the core-shell architecture effectively inhibits the interdiffusion of Hf and Zr elements, thereby preserving the toughening effect of YSZ. Thermal shock cycling tests demonstrated that the average failure lifetime of the CSYSH24 coating (208 cycles) is more than double that of the YSH24 coating (90 cycles). Consequently, the incorporation of the T’-YSZ@Al₂O₃ core-shell structure, which improves fracture toughness, yields a 131 % increase in the service life of the CSYSH24 coating compared to YSH24. These findings demonstrate the strong potential of the CSYSH24 coating for long-term stable service under ultra-high temperature conditions of 1300 °C.