Study of the performance of TBC under thermal cycling conditions using an acoustic emission rig

An experimental rig based on the use of infrared quartz lamps has been developed to monitor the degradation mechanisms causing failure of thermal barrier coatings (TBC) under thermal-cycling conditions. An acoustic emission (AE) technique monitored these degradation mechanisms, and advanced signals processing identified the key parameters that classify the AE signals according to the long-term behavior of the TBC. The AE technique enabled the localization of degradation sources inside the TBC with a linear resolution of ∼5 mm by the use of two transducers fixed at both ends of the sample. Furthermore, sample zones of high AE activity showed typical vertical cracks at the surface and delaminations at the interface between the ceramic and the bond-coat layer. Vertical cracks were induced preferentially during the heating period of the thermal cycles when the ceramic coating was in a tensile-stress state, while delaminations were induced during the cooling period when the TBC was in a compressive-stress state.