Real-time detection of damage evolution and fracture of EB-PVD thermal barrier coatings under thermal shock: An acoustic emission combined with digital image correlation method

Abstract

Thermal shock failure is the most common type occurring in service. The thermal shock life is overestimated and the failure process of thermal barrier coatings (TBCs) is still not clear due to lack of environmental simulator and the real-time detection methods. In this work, the damage evolution and failure mechanism of EB-PVD TBCs coated on a turbine vane under thermal shock is studied by acoustic emission combined with digital image correlation (DIC) method. Four damage modes are discriminated by spectrum of the acoustic emission signals, which are surface vertical cracks (200–220 kHz), sliding interfacial cracks (300–325 kHz), opening interfacial cracks (400–450 kHz) and substrate deformation (90–110 kHz). The principal strain of TBCs surface varies from compressive strain to tensile strain with increasing the thermal shock cycles. Furthermore, the thermal shock life is 710 cycles, and the exfoliation area is located in the middle of the leading edge. The failure mechanism is the propagation and coalescence of surface and interfacial cracks during the cooling stage due to the huge thermal gradient and stress concentration around the film holes.