Evaluation of in situ fracture toughness of ceramic coatings at elevated temperature by AE inverse analysis

Abstract

This paper describes acoustic emission (AE) measurement at elevated temperature by laser techniques. AE signals originated from microfracture of Al2O3/SUS304 plasma sprayed coatings were detected using a laser interferometer during thermal cycling. The radii of microcracks were evaluated by the inverse analysis of AE signals. Microcrack radii were also studied by the numerical analysis based on the delamination model for coating materials with various fracture toughness and an initial crack size at elevated temperature. In situ fracture toughness for microcracking was evaluated by combining the results of AE inverse analysis with those of numerical analysis. This approach revealed that the in situ toughness of the coatings is 40–50 J/m2, consistent with the results of a double cantilever beam test.