Crack Initiation Strength of Thermal Barrier Coating Layer under Thermal Shock

In this study, temperature differences in crack initiation of thermal barrier coating layer were examined by the thermal shock tests which is conducted by what the pencil-type specimen is dropped into the water. Crack initiation strengths of thermal barrier coating were estimated based on both of the temperature differences and the thermal stress distribution which is obtained from the closed form of thermal stress solution. Obtained results are summarized as follow. (1) It was found to be able to conduct the good thermal shock test without a gas on the specimen surface by using the pencil-type specimen with a tip angle 30°. Resistance of crack initiation in thermal barrier coating layer with a thin thickness was very high. (2) Crack initiation strength normalized by volume of the coating layer was defined newly for removing the effect of the volume on the strength. The normalized crack initiation strength corresponded to the strength of the coating materials. These results show us to be able to estimate a crack initiation strength of thermal barrier coating with a various coating thickness under a thermal shock by using the normalized crack initiation strength.