 A key feature of all TBC components is well matched thermal expansion coefficients between all layers.Thermal barrier coatings expand and contract at different rates upon heating and cooling of the environment, so materials when the different layers have poorly matched thermal expansion coefficients, a strain is introduced which can lead to cracking and ultimately failure of the coating.Cracking at the thermally-grown oxide (TGO) layer between the top-coat and bond-coat is the most common failure mode for gas turbine blade coatings.