Roles of compressive residual stress in enhancing the corrosion resistance of nano nitride composite coatings on steel

Nanocomposite coatings were synthesized, and subsequently annealed, in an attempt to understand the influence of residual stress upon their resistance to corrosion under acidic attack. Pitting corrosion, originating from microscopic coating defects, was commonly identified in the coatings subject to annealing. Finite element analysis was used to map the residual stress distribution adjacent to these defects and quantify resulting geometrical changes. The results show that with the presence of compressive residual stress in the coatings, corrosion-initiated cracking along weak interfaces was suppressed, and structural integrity maintained. Moreover, compressive residual stress helped constrict pre-existing structural defects in columnar-structured coatings and, in doing so, block the pathway of corrosive agents and limit corrosion damage to the coating–substrate interface and the substrate. The closure aspect ratio of the coating defects, defined as a new key indicator to the corrosion resistance, was numerically evaluated and quantitatively discussed for TiN coatings. Coating corrosion resistance may be improved by optimizing the residual stress in conjunction with coating thickness and the geometry of common defects.