Stress influence on high temperature oxide scale growth: Modeling and investigation on a thermal barrier coating system

In thermal barrier coating (TBC) systems, an oxide layer develops at high temperature below the ceramic coating, leading in the long term to the mechanical failure of the structure upon cooling. The mechanism of stress-affected oxidation likely to induce the growth of a non-uniform oxide scale detrimental to the TBC lifetime was investigated. A continuum thermodynamics formulation is derived accounting for the influence of the stress and strain situation at the sharp metal/oxide phase boundary on the local oxidation kinetics. It specially includes the contributions of the large volumetric strain and the mass consumption associated with metal oxidation. A continuum mechanics/mass diffusion framework is used along with the developed formulation for the interface evolution to study the growth of an oxide layer coupled with local stress development. The implementation of the model has required the development of a specific simulation tool, based on a finite element method completed with an external routine for the phase boundary propagation. Results on an electron-beam physical vapor deposited (EB-PVD) TBC case are presented. The processes resulting in a non-uniform oxide scale growth are analyzed and the main influences are discussed.