Prediction of critical rupture of plasma-sprayed yttria stabilized zirconia thermal barrier coatings under burner rig test via finite element simulation and in-situ acoustic emission technique

Abstract

In the current work, the yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) have been fabricated by atmospheric plasma spraying. The failure mechanism of the TBCs during burner rig test (BRT) has been investigated via finite element modeling (FEM) and in-situ acoustic emission (AE) technique systematically. During the BRT, the oxygen-propane flame was heated onto the surface of the coating samples with the dwell time 3 min, then the surface and the backside of the coating samples were cooled by the compressed air simultaneously for 3 min. This can be viewed as one thermal cycle. Then repeat the same heating and cooling process. The history and distribution of the temperature along the through-thickness direction of the coating samples has been obtained via FEM, and the residual stress at different stages has been also calculated. The FEM results have indicated that large tensile stress and compressive stress existed at the heating stage and cooling stage of each thermal cycle, respectively. The crack propagation tends to occur at the initial period of heating stage in the BRT process. The in-situ acquisition of the AE signals during the BRT has also been adopted. The crack propagation patterns have been obtained based on the analysis of AE signals. The filtering technique has been used to exclude the disturbance of the noise in the process of BRT in order to capture the actual and effective AE signals which represent the crack propagation and the deformation of the coating systems. Based on the characteristic waveform of effective AE signals, the Fast Fourier Transformation (FFT) and wavelet transformation has been adopted to analyze the key distribution range of the amplitude and frequency. The investigation results indicate that the acquired AE signals during BRT mainly include signals which came from the plastic deformation of the substrate and creep of each layers, propagation of the vertical crack and propagation of the interfacial cracks (horizontal crack). The detailed failure mechanisms of the TBCs during BRT have been clarified in the current work.