Fracture behavior under mixed-mode loading of ceramic plasma-sprayed thermal barrier coatings at ambient and elevated temperatures

The fracture behavior under modes I and II loading of ceramic plasma-sprayed thermal barrier coatings was determined in air at 25 and 1316 °C in asymmetric four-point flexure. The mode I fracture toughness was found to be KIc = 1.15 ± 0.07 and 0.98 ± 0.13 MPa m, respectively, at 25 and 1316 °C. The respective ‘nominal’ mode II fracture toughness values were KIIc = 0.73 ± 0.10 and 0.65 ± 0.04 MPa m. The empirical mixed-mode fracture criterion best described the coatings’ fracture behavior under mixed-mode loading. The angle of crack propagation was in reasonable agreement with the minimum strain energy density criterion.