Estimation of thermal cracking stress during spraying of thermal barrier coatings by laser AE method

Abstract

Thermal barrier coatings (TBCs) system is deposited by plasma spray method usually contain a number of cracks. These cracks can be classified into vertical and horizontal cracks and certainly affect the performance of TBCs. A monitoring method to detect the crack generation and propagation during plasma spraying is significantly required. In this study, a laser AE technique which enables in-situ and non-contact monitoring during spring process was developed to study the cracking phenomena in TBC. A new scanning pattern of the plasma torch was successfully applied to introduce only vertical cracks into the top coat. More number of AE events could be obtained by applying an improved noise filtering and multiple-threshold event detection procedures. A temperature history during spraying was also measured and used for thermal stress simulation by FEM analyses. A relationship between cracking and thermal stress in the top coat was established based on the results of AE monitoring and FEM simulation.