Evaluation Method of High Temperature Nonlinear Constitutive Equation of Top Coat Using Resonant Young’s Modulus of TBC System

Thermal barrier coating (TBC) system consists of top coat (TC), bond coat, and substrate. High temperature nonlinear stress-strain constitutive equation of TC is one of the most important mechanical properties for stress analysis of TBC system. Using a coating system specimen, the substrate prevents the specimen from rapid fracture, hence constitutive equation up to high strain is obtainable. In this study, new evaluation method for high temperature nonlinear constitutive equation of TC using the thermal stress of TC in TBC system was proposed. Changing the substrate thickness, several thermal stresses of TC under constant temperature occurred, so that we were able to obtain the stress dependent Young’s modulus which gave the nonlinear constitutive equation under constant temperature. Simultaneously, the initial residual stress at room temperature (RT) was obtainable by the proposed method. Flexural resonance method was adopted for the evaluation of Young’s modulus. Experimental data showed significant thermal stress dependent Young’s modulus for both as-sprayed TC and heat treated TC. The residual stress at RT and high temperature constitutive equation were successfully obtained by the proposed method. It was confirmed that the obtained nonlinear constitutive equation was reasonable based on the deformation mechanism of porous thermal sprayed ceramics coating.