Stress-induced roughness development during oxide scale growth on a metallic alloy for SOFC interconnects

The metallic alloys employed in solid oxide fuel cell (SOFC) interconnects rely on the growth of a protective oxide scale to sustain the aggressive functioning environment at high temperature. The morphology of the oxide/metal interface is critical to the mechanical resistance of the material system upon cooling and therefore to the component lifetime. This work investigates the development of a roughness at the oxide/metal interface, under the influence of a non-uniform stress field along the phase boundary. A small initial roughness is assumed along with a mechanism of growth stress generation with time, and a previously derived formulation accounts for the influence of the stress and strain situation at the sharp metal/oxide phase boundary on the local oxidation kinetics. A continuum mechanics/diffusion framework is formed to complete the model, and a specifically developed simulation tool is used, based on a finite element method coupled with an external routine for the phase boundary propagation. The non-uniform growth of a chromia scale over a ferritic stainless steel used in a SOFC interconnect is simulated, and coupled stress and roughness developments are investigated. The consequences regarding mechanical failure and the influence of the main parameters are discussed.