Computational design and optimization of multilayered and functionally graded corrosion coatings

This paper describes a computational approach to analysis and optimization of compositionally graded coatings for cathodic protection. Time-dependent galvanic corrosion is simulated by coupling a finite element electrochemical model with calculated rates of metal dissolution. A simulated annealing optimization algorithm is applied to the time-dependent corrosion model to determine coating structures that maximize desired protective qualities. This computational approach to coating design is applied to a hypothetical graded zinc-alloy coating with a circular defect on an iron substrate, in an aerated NaCl electrolyte. A linear compositional gradient increases the predicted duration of cathodic protection by 84% over an equivalent monolithic coating, while the optimized coating structure further improves protection time to a total increase of 112%. The optimized coating structure consists of a thin barrier layer adjacent to the substrate, with a thicker sacrificial layer on the exterior and a short region of graded composition in between. The overall approach to optimization of coating structure is shown to be robust, efficient, and produce non-obvious designs with significant improvement in coating performance, and thus has potential to be of significant utility in practical corrosion coating design.