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On the aero-engine combustor liner, a phenomenon of overheating resembling a hot spot exists, accompanied by a preferential peeling of the YSZ thermal barrier coating that will negatively affect the service life of the component. The temperature gradient of the hot spot may affect the YSZ fracture pattern.In this paper, the morphological and property changes of YSZ sintering is investigated experimentally, and a coupled analysis of the YSZ Crack Propagation Mode under the hot spot is performed using ABAQUS. The results show that the pore fractal size D of YSZ increases by 15%. Inside the hot spot region, the coating has a shear stress of 75MPa. By inserting Cohesive units globally in the model to simulate the random crack initiation and propagation, unlike the thinning of YSZ layered peeling caused by uniform superheating, hot spot will cause the crack initiation at the tip of the pores inside the coating and the oblique propagation, eventually forming an oblique crack connection through the pores. When the temperature gradient reaches 30K/mm, the crack propagation is 40% greater than in a uniform temperature field; consequently, the YSZ in the hot spot boundary region with a greater temperature gradient results in more severe bulk peeling.

The efficiency of a gas turbine engine is highly dependent upon the clearance between blades and engine case. To control the over-tip leakage, an abradable coating system is sprayed on the case surface. In the high temperature section, a ZrO2-8 wt%Y2O3 (YSZ) coating is usually applied. Pores in the coating enhance its abradability. In this study, poly-p-hydroxybenzoate (PHB) powder mixed in the YSZ powder was used as pore-forming material. To avoid burning loss of PHB during the spraying process, a sol-gel method was used to clad a TiO2 shell on the PHB powder surface. The porous YSZ coating was deposited by plasma spraying. The characteristics of the coatings were investigated in this work, such as morphology, porosity, hardness, corrosion resistance and abradability. The results show that the coated PHB increases the porosity of the YSZ coating, and then decreases the coating hardness. Finally, a rotated invading test indicates the incursion depth increases with the increase of coating porosity, suggesting the coating abradability is improved.

High velocity oxy-fuel (HVOF) spray technique has been employed to fabricate WC-17Co coatings. To achieve a high performance of mechanical properties and abrasive wear resistance, four types of WC-17Co powders with different feedstock particle sizes were investigated. The results show that the feedstock powder with finer particle size has higher velocity and temperature during the spraying process, resulting in a denser coating and a stronger splat-splat bonding. The micro-hardness of WC-17Co coating increases with the decreasing of feedstock size. The coating deposited by finer feedstock powder has superior abrasive wear resistance, due to the smaller porosity and boundary flaws on coating surface. However, coating fracture toughness could be affected by feedstock size if it is too small. Among all those investigated coatings, the one with medium particle size and narrow size distribution exhibits both excellent mechanical properties and wear resistance.

An Inconel 718 alloy was coated by WC-17Co using a high-velocity oxygen fuel (HVOF) thermal spray process. The residual stress of WC-17Co coating under different heat-treatment conditions was investigated. The effect of residual stress on bending fatigue life of the coated alloy was discussed. Results show that fatigue cracks are initiated at the WC-17Co coating and propagated to the alloy substrate. The compressive residual stress generated during HVOF process could restrict the initiation and propagation of cracks. The absolute value of the compressive residual stress in WC-17Co coating decreases after annealing treatment, resulting in a lower fatigue life of the coated specimens.

WC-17Co cermet coatings were deposited on Ni718 alloys using the high-velocity oxygen fuel (HVOF) technique. These coatings were then heat treated by different processes (150 °C, 10 h; 300 °C, 10 h; 450 °C, 10 h). The effects of heat treatment on microhardness, elasticity modulus, and fracture toughness were studied by an indentation method. The residual stresses of the coated specimens were evaluated by the Almen strip method. The results show that the phase constitution and the structure of the WC-17Co coatings exhibit no obvious change in 150, 300, and 450 °C heat-treatment. The microhardness, elasticity modulus, and fracture toughness of the WC-17Co coatings decrease with the increase of heat treatment temperature. The descent tendency of the mechanical properties is attributed to the decline in compressive residual stresses after isothermal heat treatment.