Stress evolution in ceramic top coat of air plasma-sprayed thermal barrier coatings due to CMAS penetration under thermal cycle loading

Abstract

Failure in the top coat (TC) induced by CaO-MgO-Al2O3-SiO2 (CMAS) penetration is one of the most serious threats to the performance of air plasma-sprayed thermal barrier coatings (APS TBCs) under thermal cycle loading. Thus, understanding the evolution of CMAS penetration induced stress in TCs under such loading is crucial to prolong the life of APS TBCs. In this study, a multi-layer model of an APS TBCs system incorporating the microstructures of the TC is established to numerically investigate the cyclic stress behavior in the TC during 10 thermal cycles under CMAS attack. The results show that thermal cycle loading aggravates the stress state around the microstructure in the TC during cooling and may further initiate mixed crack types here. Prolonging the holding time of thermal cycles also aggravates the stress state in the TC due to the accumulated unrecoverable creep deformation around the microstructure. The cyclic stress behavior in the TC under different depths of CMAS penetration demonstrates that the TC/bottom coat (BC) interface has a significant influence on the stress level of the CMAS-penetrated interface, especially as the latter approaches the TC/BC interface.