Effects of Al2O3 Particle Size on Multi-Mode Erosion Failure Mechanisms of EB-PVD YSZ Thermal Barrier Coatings Under Simulated Aero-Engine Conditions

To investigate the influence of particle size on the erosion damage behavior and failure mechanisms of thermal barrier coatings (TBCs) in a simulated aero-engine erosion environment, erosion tests were conducted using Al2O3 particles of different sizes (65 μm, 120 μm, and 175 μm) under a nominal gas-flow condition of Mach 0.4 at 1150 °C with custom-built multi-factor coupled erosion test equipment. TBCs were prepared using electron beam physical vapor deposition (EB-PVD). By combining macroscopic/microscopic morphology, composition, white-light interferometry, and Raman residual stress testing, the damage evolution and failure behavior of TBCs under different particle size conditions were analyzed. The results indicate that particle size has a significant effect on the erosion behavior of thermal barrier coatings. Under erosion conditions involving 65, 120, and 175 μm particles, the erosion rates were 10.83, 4.19, and 2.05 g/kg, with corresponding coating lifetimes of approximately 3, 12, and 22 h. As particle size increases, the erosion rate decreases and the coating lifetime increases. Under small 65 μm particles, the coating exhibits high-frequency continuous micro-cutting. The ceramic layer rapidly thins, leading to localized penetration. Under erosion by 120 μm particles, the coating exhibits a composite damage mechanism involving cutting, compaction, and brittle fracture. Under large-particle impacts of 175 μm, the damage mechanism is dominated by localized brittle fracture and spalling induced by high-energy impacts. Although the single-impact energy of large-particle impacts is higher, the lower particle number density results in a discrete distribution of damage zones, leading to a lower material removal rate. The Raman test results further indicate that, after 2 h of erosion, the differences in residual stress in the TGO layer were relatively small across different particle size conditions, suggesting that the early degradation process of the coating is primarily controlled by the mechanical removal of the ceramic surface layer rather than by the evolution of TGO stress. No statistically significant difference in TGO residual stress was observed among different particle sizes after 2 h of erosion (p > 0.05). Not only is the erosion life of EB-PVD YSZ TBCs is influenced by the impact energy of individual particles, but more importantly, it is also closely related to particle number density, impact frequency, and the spatial distribution of damage.