Improved corrosion resistance of TiMgN coating through filling grain boundaries and forming passive layer by Mg-containing oxides

Abstract

Transgranular corrosion is widely considered to be the main reason for the premature failure of coatings prepared by magnetron sputtering technology in salt spray environment. Considering the high chemical reactivity of Mg, so that Mg is incorporated into the TiN coating as a sacrificial anode component to improve the salt spray corrosion resistance. Specifically, part of the doped Mg is dissolved into the TiN lattice to form (Ti, Mg) N solid solution by replacing Ti atoms, and the other part forms amorphous Mg₃N₂ phase. After 336 h in salt spray environment, the surface of TiMgN coating containing 35 at% Mg has no cracks that can accelerate localized corrosion and promote dissolution beneath the substrate. In the early stage of corrosion, O₂ and corrosive medium mainly penetrate the coating along the grain boundaries. The high chemical reactivity of Mg can promote formation of oxides (MgO, TiO₂). MgO and TiO₂ aggregating at the grain boundaries can seal structural discontinuities to enhance coating densification and hinder the further penetration of corrosion medium. With the increase of corrosion time, the formation of continuous and dense surface passive layer (MgO, TiO₂ and Mg(OH)₂) reduces corrosion rate. The MgO/Mg(OH)₂ acts as a physical barrier against Cl^- penetration and the inherent corrosion resistance of TiO₂ enhances passivation stability and reduces the dissolution of the passive layer.