Determining the fracture toughness of ceramic coatings by relative method

The fracture toughness of a ceramic coating is an important parameter for the application of coated components, but it is hard to be measured because the coating is usually too thin to be stripped directly from the substrate and tested as a block material. In this study, an effective technique to determine the fracture toughness of coating was proposed. An analytical relationship among the fracture toughness of the coating, substrate sample, and coated sample were derived, so that the fracture toughness of the coating can be calculated from the measured toughness of the substrate and coated samples. This indirect test is called relative method. By this simple method, the fracture toughness of SiC coatings on graphite substrate and on C/C composite substrate were evaluated respectively based on tests of single edge V-notched beam method (SEVNB). The results indicate that the relative method is convenient and feasible for evaluating the fracture toughness of ceramic coatings.