The Study Of Dense Vertically Cracked TBCs Prepared By High Energy Plasma Spraying

Against the early failure of TBCs during service, it’s expected to prepare densevertically cracked TBCs to extend the lifetime of TBCs. In this paper, influences of thedeposition, temperature of the substrate, and the roughness on the preparation of densevertically cracked (DVC) TBCs were studied, and then the failure mechanisms of TBCswith or without vertical cracks during thermal shock test were discussed.It was found that vertical cracks can be achieved by controlling the deposition, thesubstrate temperature and the roughness. It was beneficial for preparing vertical crackswhen the deposition was20μm, the substrate temperature was between650℃to800℃and the roughness was about4μm. When the deposition increased to40μm, the horizontalcracks appeared; when the substrate temperature increased from650-725℃to725-800℃,the density of vertical cracks increased from1strip/μm to2strips/μm; when theroughness increased from4μm to6μm, vertical cracks vanished. Compared withTBCs without vertical cracks, the lifetime of DVC TBCs was not improved obviously dueto the oxidation of bond coatings during spraying. Failure mechanisms of TBCs withoutvertical cracks mainly included:(1) initiation of vertical and horizontal cracks;(2) thespalling of surface particles;(3) formation of different forms of TGO: single layer TGOmade up of Al2O3, double layers TGO made up of Al2O3and spinals and roundaboutstructure. Failure mechanisms of DVC TBCs mainly included:(1) propagation of verticalcracks;(2) initiation of horizontal cracks around vertical cracks;(3) formation of TGOsimilar to TBCs without vertical cracks.