Reliability Assessment On Interfacial Failure Of Thermal Barrier Coatings By JC Method

Thermal barrier coatings (TBCs) have been widely used in aircraft and industrial gas-turbineengine due to their excellent high temperature resistance, corrosion resistance, thermal shockresistance and fuel-consumption reduction. However, because of the complexity of thermalbarrier coatings in geometry, microstructure and operation circumstance, the fracture andspallation of coating cannot be predicted, which is greatly limited the application of thermalbarrier coatings to aircraft engine. Therefore, the study of the TBCs failure and reliabilityevaluation, which effectively prevent the failure of coating, is a key to aerospace. In this paper,according to two different TBCs made by air plasma spraying (APS) and electron beam physicalvapor deposition (EB-PVD), the reliability of interfacial failure are evaluated based on equivalentnormal random variable of the method of reliability analysis(recommended by JCSS, so-called JCmethod). The main contents of this thesis are listed as follows:Firstly, the interfacial buckling failure of APS-TBCs under axial compression and theinterfacial shear failure of APS-TBCs under shear load were evaluated. Combined thecompression experiment with acoustic emission technique (AE), critical stress of interfacialfailure in TBCs was achieved. It was found that the critical stress obeys the Weibull distribution.Based on the failure criterion, the limit state equation was established and we predicted the failureprobability of interfacial buckling under different compression loads. The interface shear strengthwas obtained by shear experiments. The failure probability of TBCs interfacial shear failure waspredicted under different shear loads. Considering both compression and shear loads, the failureprobability of TBCs is also calculated.Secondly, the delamination of APS-TBCs considering the crack propagation and theinterfacial oxidation failure of EB-PVD TBCs were estimated. On the basis of the failure criterion,the limit state equation was established. Random statistical nature of different parameterscontributed to failure was analyzed. By means of JC method, the failure probability ofdelamination and interfacial oxidation under different conditions were calculated. Takingadvantages of the sensitivity analysis method, the sensibility factors of different parameters wereobtained, which were used to analyze the effect on the interfacial oxidation.Thirdly, the parameters, which were correlateed with the failure of TBCs, such as thedelamination of APS-TBCs considering the crack propagation and the interfacial oxidation failureof EB-PVD TBCs, were reduced by the method of dimensional analysis. The non-dimensionalparameters were simple classified, then they were used to sensitivity analysis. In general, on the view of probability statistics, the thesis analyzed the reliability assessmentof interfacial failure of TBCs by applying the MATLAB program, which is based on thereliability assessment of JC method. The research results of the thesis can provide the importantbasis and reference for the further research on reliability assessment of TBCs and widen theapplication of reliability assessment analysis method.