Factors in the degradation of ceramic coatings for turbine alloys

Internal stresses introduced during the processing of ceramic coatings for turbine components can lead to coating failure. The sources of such stresses include not only the thermal expansion mismatch between ceramics and metals but also elastic anisotropy and thermal gradients introduced within the ceramic during plasma spraying or phase transformations (e.g. in ZrO₂). However, the ceramic coatings can be made more resistant to fracture (or spalling) by control of their microstructure. The ability of ceramic coatings both to resist corrosion and to protect the metallic components presents additional challenges to the development of coatings.