Damage evolution in EB-PVD thermal barrier coatings under coupled thermal shock and CMAS + sea salt corrosion: a real-time acoustic emission study

Thermal barrier coatings (TBCs) in marine environments face severe degradation from coupled thermal shock and CMAS + sea salt corrosion. This study utilizes real-time acoustic emission (AE) monitoring to investigate the damage evolution and failure of electron beam physical vapor deposited (EB-PVD) TBCs under these conditions. Using self-organizing map (SOM) neural networks, agglomerative hierarchical and K-means clustering, four characteristic AE damage modes are identified by peak frequency: substrate deformation (10–80 kHz), surface vertical cracks (90–235 kHz), sliding interface cracks (246–370 kHz), and opening interface cracks (378–500 kHz). AE signals concentrate in heating and cooling stages. Significant AE events from surface vertical cracks, opening and sliding interface cracks indicate their rapid propagation and dominance throughout the cooling stage, confirming that coating failure typically occurs during cooling. Sliding interface cracks are the dominant mode in TBCs, followed by surface vertical cracks and opening interface cracks during thermal cycles. The mechanism involves CMAS/sea salt permeation causing interfacial corrosion and damage, where residual stresses drive rapid propagation of sliding and opening interfacial cracks, leading to spallation.