Plasma Sprayed 8YSZ Thermal Barrier Coatings Failure Mechanism And Microstructure

Thermal barrier coatings (TBCs) are used to thermally protect metallic in gas-turbine engines used for propulsion. Air plasma sprayed is an effective way to prepare TBCs, due to its advantage of low cost, TBCs with low thermal-conductivity at high temperature, etc. Despite the increased use of thermal barrier coatings, premature spallation failure during service is still a concern. The initiation and propagation of cracks were simulated using long heat treatment processes, and the failure mechanisms related to coating's microstructure were investigated using Scanning electron microscopy (SEM), Electron backscatter diffraction (EBSD) and Focused ion beam (FIB), it has made important progress particularly in the following areas:(1) The phase transformation in the bond coat layer after long heat treatment is clear, by using EBSD and XRD;(2) Cracks propagation along the grain boundaries of the TGO was confirmed by EBSD mapping, local-misorientation mapping indicating that the strain at the grain boundaries, especially in the crack path, is greater than in intra-crystalline TGO;(3) First to give three dimensional evidence that crack propagation in top coat, and explains the phenomena as well as its results of crack growth;(4) This suggested that the growth of TGO is controlled by the diffusion of Al and Ni.lt was confirmed that Ni and A1 diffused along the GBs of YSZ, promoting the further growth of TGO towards the YSZ layer. A method has been developed to accurately determine TGO thickness.