Quantitative acoustic emission analysis of plasma sprayed thermal barrier coatings subjected to thermal shock tests

Thermal shock behavior of plasma sprayed thermal barrier coatings (TBCs) under cyclic laser thermal shock was studied by quantitative acoustic emission (AE) analysis. AEs from TBCs during cyclic heating/cooling were monitored as function of coating thickness, existence of bond coating and laser energy. Fracture dynamics (kinematics and fracture mode) were studied by waveform simulation of the AE signals monitored by displacement sensitive sensor. Vertical fracture (Mode-I) in the ceramic top layer was identified as the primary cracking in the first several cycles, and interfacial fracture (Mode-I and II) became predominant for thick top layers or specimens without a bond layer under high laser power irradiation. Progression and mechanisms of coating damages were revealed as a function of temperature and microstructure.