A parametric study of the Double-Ceramic-Layer Thermal Barrier Coating Part II: Optimization selection of mechanical parameters of the inside ceramic layer based on the effect on the stress distribution

• The TC2 layer has the stress buffer effect to reduce the stress of the TC1.
• The ρ of TC2 should be neither too high nor too low.
• The “general safety region of E–ρ” is concluded.
• 47.796 GPa–10.8029/°C(× 10− 6) is the best point of E–ρ.
• The rationality of selecting the 8YSZ as TC2 has been confirmed.

The Double-Ceramic-Layer Thermal Barrier Coating (DCL-TBC) consists of a top ceramic layer, an inside ceramic layer, bond coat (BC) and alloy substrate. The introduction of TC2 has the effect of stress buffer to TC1, which causes the stress of TC1 decreased. In this situation, the typical material parameters ρ and E of the inside ceramic layer will have great influence on the stress distribution and ultimate life of the DCL-TBC. Based on this, the first part of the present paper is to investigate the effect of the typical material parameters ρ and E of the TC2 on stress distribution in the DCL-TBC with the thickness ratio of TC1 and TC2 as 150 μm–150 μm, using the finite element method. From mass calculation, the influences of the material parameters ρ and E upon the stresses of TC1 and TGO are presented in the paper.Secondly, the typical material parameters ρ and E of the TC2 is optimized and selected based on the optimization criteria which are “the stress of the TC1 is in safe state” and “the TGO has the lowest stress level”. Aiming at the criterion based on the safety of the TC1, “general safety region of E–ρ” and “E–ρ general safety boundary” are concluded in the stress map of E–ρ. Based on the criterion of the lowest stress level in TGO, it has been concluded that the point of 47.796–10.8029 is the best point of E–ρ, i.e. the DCL-TBC has the best life if the modulus E and thermal expansion coefficient ρ of the inside ceramic layer are 47.796 GPa and 10.8029/°C(× 10− 6).