Investigation of crack propagation behavior of thermal barrier coatings fabricated by atmospheric plasma spraying in the process of uniaxial tension using acoustic emission technique

摘要

To characterize the adhesive strength of the plasma sprayed thermal barrier coatings (TBCs) via uniaxial tension is a common technique. In this paper, the crack initiation, grow and propagation behavior in the atmospheric plasma sprayed (APS) TBCs in the process of uniaxial tension test has been investigated using the acoustic emission (AE) technique, X-ray diffraction (XRD), scanning electron microscope (SEM) and finite element method (FEM). The experimental results indicated that the position of the crack initiation is usually located in the inner of the ceramic layer, and the crack tend to propagate along the tension direction and some key horizontal cracks reach to the metallic layer/ceramic layer interface, then the vertical cracks which initiate at the lower middle of the horizontal cracks propagate along the interface. When some big enough cracks was formed at the interface and a series assembled splats separated from the coating, the coating totally failure. The AE signal can be divided into three typical stages which correspond to the three stages of the stress-stain curve of the tension. The detailed analysis of the AE signal has been performed. The dynamic propagation patterns of the key cracks in the ceramic layer during the tension process have been simulated using FEM. The finite element simulation results have further proved our conclusions drawn from the experimental results.