Effects of the combined vacuum pre-oxidation on the microcracks initiation and propagation of thermal barrier coatings deposited by means of plasma spraying

摘要

The chemical compositions and the residual stress of the thermally grown oxides (TGO) of thermal barrier coatings (TBCs) were characterized. Moreover, the relationship between the initiation and propagation of the microcracks in top coat and the evolution of TGO were systematically studied. The results indicate that the degradation mechanisms of TBCs prepared by atmospheric plasma spraying probably result from the weakened TGO area which is closely related to the change of the alumina phase transformation and the excessive presence of the spinel oxides as well as the propagation of the vertical surface cracks. Generally, the vertical surface cracks will propagate to the TGO area and subsequently meet with the horizontal cracks adjacent to the upper 50 mu m area from the TGO. However, the propagation of the vertical surface cracks will be markedly suppressed when the strengthened TGO area occurs; while the initiation and propagation of the horizontal cracks above the TGO area can be significantly suppressed because the specific cracks aggregation can be found in the top coat. Furthermore, the textured (Al, Cr)(2)O-3 formed at the bottom layer of TGO can strengthen the oxidation and corrosion resistance of TGO. The maximum magnitude of the steady state release rate G(ss) can be delayed in the top coat, which can prolong the lifetime of TBCs. (C) 2015 Elsevier Ltd. All rights reserved.