Computational parametric study for plastic strain localization and fracture in a polycrystalline material with a porous ceramic coating

Abstract

Polysilazane-based ceramic coatings have ever-increasing applications in critical and high-power engineering. This paper analyzes the effects of the substrate grain size, the curvature of the coating-substrate interface and the pore-free coating layer on the plastic strain localization and fracture of the porous ceramic coating–polycrystalline substrate structures under compressive loading applied to the coated surface. Models for generating pore and polycrystalline structures of the coating and substrate are developed, with the experimentally observed microstructures of the coated steel being taken into account in calculations explicitly as the initial data of the boundary-value problem. Numerical results obtained by the finite-difference method show that the crack-initiation strain depends on the substrate grain size exponentially. A comparison between the models with serrated and plane coating-substrate interfaces suggests that in the former case, coating cracking initiates near the humps of the interface concavities and the top and bottom pore surfaces, while in the latter case, two sites of cracking nucleation can be distinguished, namely, close to the pores – in the fine-grained substrate, and near the coating-substrate interface – in the case of coarse grains. The results indicate that it is preferable to use the coated specimens characterized by a serrated coating-substrate interface.