A mechanistic study of oxidation-induced degradation in a plasma-sprayed thermal barrier coating system. Part II: Life prediction model

A parametric study is conducted to quantify the effects of different micros tructural variables and service conditions on the local stresses induced by oxidation, sintering processes and thermal cycling in a typical plasma spr ayed thermal barrier coating (PS-TBC) system. The study relies on the numer ical results obtained from a continuum mechanics-based mechanistic study of the oxidation-induced degradation of the PS-TBC system. Analytical express ions are presented for the peak out-of-plane stress component which promote s the nucleation and growth of mesoscopic cracks within the top zirconia-ba sed ceramic coating in terms of thermal cycle parameters, and accumulated o xidation time. Based on the results of the parametric study, a damage mecha nics-based life prediction methodology for the failure of the PS-TBC under thermal fatigue loading conditions is proposed. The model assumes that PS-T BC failure occurs by a cleavage-type mechanism within the top zirconia coat ing, in agreement with experimental evidence, and that the accumulation of damage with thermal cycling is linked to the gradual degradation of the int rinsic cleavage strength of the zirconia. The model is shown to be capable of predicting consistently a broad range of thermal fatigue data. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved .