Reliability assessment and lifetime prediction of TBCs on gas turbine blades considering thermal mismatch and interfacial oxidation

Abstract

Thermal barrier coatings (TBCs) – as porous ceramic materials – have varying lifetimes because of their unstable mechanical properties and harsh working conditions. In this paper, a probabilistic approach to quantify the risk of interface spallation in TBCs by thermally grown oxide (TGO) growth and thermal mismatch, along with a lifetime prediction method based on the critical failure probability is proposed. First, a failure criterion for TBCs is set to determine a boundary between the failure and safe region. Second, parameters relating to failure, along with the stochastic characteristics of these parameters, are analysed thoroughly. Third, the failure probability is calculated. Finally, the lifetime of TBCs on turbine blades in a hot gas stream is predicted. Under furnace isothermal cycling, the predictive failure probabilities of TBCs are 0.1% (300 cycles), 1.5% (600 cycles), and 7.49% (1000 cycles). The experiment results for turbine blades are 1.03% (300 cycles), 1.73% (600 cycles), and 5.12% (1000 cycles). Under a hot gas stream, the maximum failure probabilities of TBCs after 200, 300, 500, and 1000 h are 40%, 45% 50%, and 70%, respectively. The lifetimes of TBCs are 273, 332, 406, and 523 h if the critical area ratio of the metal substrate exposed to the hot gas is 5%, 10%, 15%, and 20%, respectively.