Quantitative characterization of the interfacial failure of metallic coatings on epoxy substrates in salty atmospheres

Abstract

Although a multilayered metallic coatings on epoxy surfaces can enhance material performance, under acidic and salty conditions, such as sweat, the coatings usually delaminate from polymer surfaces. Therefore, we investigated the interfacial failure of a Ni/Ag/Ni coating on an epoxy surface after long-term exposure to salt spray air or artificial sweat containing abundant Cl− ions. Cross-sectional atomic force microscopy and X-ray photoelectron spectroscopy were used to probe the changes in the interfacial morphologies and depth profiles of the chemical composition, respectively, to elucidate the mechanism by which Ni/Ag/Ni trilayered coatings delaminate from epoxy substrates in Cl−-containing atmospheres. The results revealed that Cl− ions penetrated through the epoxy, diffused into the metal–polymer interface, and dissolved the Ni layer at the epoxy surface, detaching the metallic layer from the polymer surface. In response to the failure mechanism mentioned above, we propose that by partially replacing the Ni primer layer with Ni2O3, which is inert in acidic Cl− atmospheres, the Ni2O3/Ni/Ag/Ni coating strongly resists corrosion in salt spray air and possesses good long-term interfacial bonding under acidic Cl− atmospheres. The mechanism of interfacial failure of Ni/Ag/Ni coating on epoxy surface after long-term treatment in air of artificial sweat were evaluated by cross-section AFM and XPS depth profiling. It was revealed that Cl ions penetrate the epoxy substrate, diffuse into metal-polymer interface and dissolve the primer Ni layer, resulting a delamination of metal coating from epoxy substrate. A Ni₂O₃ layer was introduced to construct the Ni₂O₃/Ni/Ag/Ni structure, which exhibits superior interfacial bonding performance in acidic Cl− atmosphere.