2008 Volume 72 Issue 5 Pages 317-322
In order to clarify different manners of failure behavior for plasma sprayed thermal barrier coating (TBC) systems under the complicated modes of thermal-mechanical-chemical loadings, the stress rupture properties was evaluated in air and in high-temperature corrosive environment with relation to the failure analysis for two kinds of TBC systems produced by different bond-coat (BC) processing. CoNiCrAlY-BC was manufactured by a vacuum plasma spraying (VPS) or high velocity oxy-fuel (HVOF), and then the Y2O3-stabilized ZrO2 top-coat (TC) was made by an atmospheric plasma spraying (APS). After then, heat-treatment was adopted for the sprayed TBC specimens in pure argon atmosphere.
TBC system with HVOF-BC was found to result in the almost equivalent rupture life to that of VPS-BC, because the compositional and microstructural modification; equalization, of the HVOF-BC was attained by the heat-treatment. Furthermore, it was found that the strength properties of both TBC systems depend strongly on the loading condition. Namely, the static creep loading was found to cause the almost similar rupture life to the no-coated substrate superalloy for both TBC systems regardless of the environmental condition. On the contrary, the dynamic fatigue and creep-fatigue loadings tend to bring about a significant rupture life reduction, since the penetration crack induced by the heat-treatment in the TC provides directly the nucleation site of the fatigue main crack.
