Acoustic Emission and Associated Damage Mechanism Analysis in 8YSZ Thermal Barrier Coatings Under Instrumented Indentation

Acoustic emission (AE) monitoring was used during indentation tests on the cross section of plasma-sprayed 8 wt.% yttria-stabilized zirconia (8YSZ) thermal barrier coatings to investigate the relationship between AE signals and the associated deformation or single cracking events. The damage evolution in 8YSZ was studied by examining signal characteristics with the aid of AE parameter analysis and wavelet packet decomposition. The results show that the coatings were firstly elasto-plastically deformed, and microcracks gradually developed around the indentation. Then, delamination occurred and the fracture was made up of some longer cracks and dozens of microcracks. AE signals originating from coating deformation, formation of microcracks and longer cracks show different amplitudes and frequencies. The results indicate that the features of AE parameters differ depending on the mechanical failure mechanism, and AE responses are closely related to the fracture behavior and are dependent on splat microstructure of the coatings.