Determination of Interface Fracture Toughness in Thermal Barrier Coating System by Blister Tests

The theoretical model for the blister test method was used to analyze the interface fracture toughness of zirconia coating deposited on an SUS304 stainless steel substrate by a plasma-spraying method. The elastic parameters of the debonded coating were determined by testing the oil pressure q and maximum deflection w(0). SEM observation, compliance method and ultrasonic detection were used to determine the radius of the debonded coating. The three methods gave the same results for the debonded coating radius. Micro-observations showed that the interfacial crack propagates by the growth of voids or microcracks ahead of the main crack and coalescence with the main crack. The energy release rate G 0 with phase angle ψ=0 for type A coating and type B coating was, respectively, 14.54∼25.88 J/m 2 and 11.88∼16.21 J/m 2 . The corresponding interface fracture toughness for type A TBC coating and for type B TBC coating is, respectively, 0.77∼1.02 MPa.m 1/2 and 0.52∼0.61 MPa.m 1/2 . The stable phase angle was approximately -31.5° and -30.2° for coating A and coating B. respectively.