Either to obtain desirable microstructures by adjusting processing parameters or to predict the properties of a thermal barrier coating (TBC) according to its microstructure, fast and reliable quantitation of the microstructure is imperative. In this research, a machine-learning-based approach—a deep convolution neural network (DCNN)—was established to accurately quantify the microstructure of air-plasma-sprayed (APS) TBCs based on 2D images. Four scanning electron microscopy (SEM) images (view field: 150 μm × 150 μm, image size: 3072 pixel × 3072 pixel) were taken and labeled to train the DCNN. After training, the DCNN could recognize correctly 98.5% of the pixels in the SEM images of typical APS TBCs. This study demonstrated that a small dataset of SEM images could be enough to train a DCNN, making it a powerful and feasible method for quantitively characterizing the microstructure osf APS TBCs.

The failure mechanism of a thermal barrier coatings (TBCs) system is investigated using cyclic thermo-mechanical loading with a thermal gradient. Hollow circular cylindrical specimens are employed, consisting of a nickel-based single-crystal alloy DD6 coated with a NiCoCrAlYHf bond coat via arc-ion plating and a surface electron beam physical vapor deposited (EB-PVD) yttria-stabilized zirconia topcoat. The experimental setup allows for a surface temperature of 1130 °C and a substrate temperature of 1070 °C, while a tensile mechanical load of 200 MPa is employed to simulate the centrifugal stress in the middle of the high-pressure turbine blade. The comparison between TBCs with and without mechanical loading implies that the coupled thermo-mechanical load significantly promotes coating spallation since the superposition of mechanical strain enhances the local tensile stress at the peak region of the topcoat/thermally grown oxides (TGOs) interface. A subsequent interfacial morphology analysis demonstrates that the topcoat/TGO interface exhibited a degradation in the direction parallel to the mechanical loading axis. For all the specimens, TGO comprises a duplex structure, consisting of outer spinel and inner α-Al₂O₃.

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.

To simulate the erosion damage behavior of thermal barrier coatings (TBCs) under actual service conditions in an aircraft engine environment, this study developed a multi-factor coupled test setup capable of simulating combined loading under high-temperature (1150 °C), high-speed (0.4 Mach), and solid-particle erosion conditions. Yttria-stabilized zirconia (YSZ) TBCs were prepared using electron beam physical vapor deposition (EB-PVD). For different erosion durations (2 h, 5 h, 8 h, 12 h), the evolution of macroscopic and microscopic morphologies as well as the development of residual stresses in the thermally grown oxide (TGO) layer were systematically investigated. The results indicate that the erosion process of the YSZ coating can be divided into three stages. During the initial high-erosion-rate stage (8.17 g/kg), erosion damage was confined to the grain tips of the columnar crystals, primarily caused by brittle fracture at the grain tips, and the TGO stress was relatively low (−0.6 GPa). During the intermediate stage, the erosion rate was lower (2.74 g/kg). Impact stresses induced microcracks within the columnar grains, which gradually connected to form intergranular fractures. This led to the expansion of localized spalling pits. The interface began to wrinkle, and the stress rose to −2.2 GPa. In the final accelerated failure stage (5.88 g/kg), horizontal cracks fully propagated, leading to large-scale peeling of the coating. The stress was released to −0.9 GPa. The coating failure mechanism evolves from surface damage to interfacial peeling, which is closely related to the coating structure, stress evolution, and interfacial state.