A new double-layer sol-gel coating to improve the corrosion resistance of a medical-grade stainless steel in a simulated body fluid

One of the effective ways to overcome some of the drawbacks of oxide coatings for corrosion protection of metal surfaces is the incorporation of an organic component into the inorganic network, although, commonly, film adhesion is disadvantageously affected. In this work, for the first time, by exploiting both inorganic and organic-inorganic coatings, a new double-layer thin film, which comprises ZrTiO₄ as the bottom layer and ZrTiO₄-PMMA as the top layer, was deposited on a medical-grade stainless steel substrate via a sol-gel spin coating method. According to potentiodynamic polarization experiments in a simulated body fluid, the substrate coated with this film exhibited superior corrosion resistance, compared with the same steel coated with purely inorganic ZrTiO₄ and hybrid ZrTiO₄-PMMA films. The superior corrosion resistance of the newly developed coating was found to be due to simultaneously the good adhesion of the lower, inorganic film and the low defect density of the upper, hybrid film.