Simple formulas for thermoelastic stresses in TBC coatings

Thin coatings on metallic substrates are extensively used in mechanical, aerospace, microelectronic, optical, and medical applications. Coatings affect the surface properties of the system, while bulk properties and strength primarily depend on the substrate. In coated components subjected to thermal cycling, differences in physical properties and chemical nature between constituent parts of coating and substrate can cause thermal stresses, atomic diffusion, and chemical interactions, which decrease high-temperature stability and actual strength of the system. In this article, the microstructure of a thermal barrier coating is briefly described; then, the temperature field inside the coating is calculated from a transient or a steady periodic state analysis; hence, thermomechanical stresses are analytically determined for a double-layer system with planar or axisymmetric geometry. The present analysis leads to new formulas with which temperature and stress fields can be calculated.