Design And Study Of SiC Fiber Reinforced ZrO₂Thermal Barrier And Ablative Thick Composite Coating

Analytical model of the coating stress based on the composite beam model andLame equation is built for the air plasma spraying process, which is used to study theresidual stress of the coatings. The analysis results reveal that cylinder geometry is moresuitable for the thick thermal barrier coatings than the planar geometry. It is testedthat the thickness of the coatings with planar and cylinder geometry are1.8mm and2.5mm respectively.According to the analytical model, the radial compressive stress produced by thewrapped fibers stopped the extension of the cracks so that the bonding strength andthe maximum thickness limit are improved dramatically. Due to the toughening effectof the continuous fibers, the mechanical properties especially the cohesion strength ofthe coating will rise a lot.Continuous SiC fibers was used in the experiments based on the excellentmechanical properties and high-temperature behavior. According to the analyticalmodel of coating stress and fiber properties, the SiC fiber reinforced ZrO2thermalbarrier and ablative thick composite coating is designed as a fiber wrappedmulti-layer structure.Copper and POB as ablation materials in the air plasma spraying process, whichshows that they are not suitable for preparing the composite thick coatings. Thedeposition thickness of the n-ZrO2powders is only6.8μm while the bonding strengthof the coating is9.37MPa. In the mechanics performance testing the n-ZrO2coatingsfractured inside so that the cohesion strength is too bad for manufacturing compositethick coatings. The deposition thickness of the μ-ZrO2powders in the range of30μm-40μm is24.0μm while the bonding strength of the coating is19.5MPa. Thermal conductivity of the μ-ZrO2coating is as low as0.54W/m·K. Takingmechanical properties, deposition efficiency and heat-insulating capability intoconsideration, the μ-ZrO2powders are used to produce the composite thick coatingsin the experiments.10%SiO2/ZrO2composite powders are used to produce the fiber protectivelayers in the experiments. Adding SiO2into the composite powders raise the liquid content of the droplet which decreased the impact effect of the droplet to protect thefibers. At the same time, excellent film-forming properties of SiO2improved thecombination between fibers and protective layers to make sure toughening andreinforcing effects of the fibers.This paper designs an experiment method to study the SiC fiber reinforced ZrO2thermal barrier and ablative thick composite coating. A thermal cycling test and anablation test are carried out to evaluate the performance of the composite thickcoating. Experiment results reveal that the protective layers raise the antioxidantcapacities of the fibers while the phase transformation of SiO2takes away a lot of heatenergy to keep the coating and fibers in the safety temperature range. Because of theeffect of SiO2the ablative properties of the composite thick coating rise a lot.