Influence of crack features on heat transfer characteristic and cracking behaviour of APS-YSZ coating: A numerical simulation study

Abstract

Spallation of air plasma sprayed (APS) thermal barrier coatings (TBCs) is a decisive factor that dominates the lifetime of APS-TBCs. It is noticeable that coating spallation is correlated with the crack initiation and propagation. The cracks will influence the temperature field and other characteristics of the coating. It is of great importance to sufficiently comprehend and specify these characteristic indexes (such as temperature gradient, thermal conductivity and elastic modulus) of coating changes that the crack evolution brings. In this study, the numerical reconstruction models of TBCs with different major crack lengths and openings were obtained. By using the thermal lattice Boltzmann method (TLBM) and finite element model, the precise temperature field and heat flux distribution of coatings were obtained. The thermal and mechanical properties of coatings were also investigated. The results showed that, the effective thermal conductivity and Young’ modulus of the top coat decrease with the increase of major crack length and opening. At the same time, the energy release rate shows a faster increase for small cracks and its increase trend slows with crack growth. Crack opening further increases the growth of energy release rate. Although the horizontal crack can reduce the thermal conductivity and modulus of the coating, the crack can induce coatings failure. In addition, the extension and expansion of crack will lead to more non-uniform distributed heat flux and larger temperature gradient in the top coat. These results can provide an informed basis for reliable assessment of performance integrity of APS-TBCs. The structural reconstruction and properties analysis models can also be applicable to the field of porous media.