Evolution of mechanical and corrosion properties of TiN/TiO2 nanocomposite multi-stage coating on AZ31 magnesium alloy using atomic layer deposition and in-situ oxidation

Abstract

TiN/TiO2 nanocomposite film has been deposited on AZ31 magnesium alloy by two-step preparation involving atomic layer deposition and in-situ oxidation. The compact single and multi-stage coatings uniformly cover the surface. Mechanical property evaluation indicates that the resulting coating has good adhesion strength, well wear resistance and compressive residual stress. Furthermore, neutral salt spray test shows a uniform corrosion mode. Hydrogen evolution and electrochemical tests indicate excellent corrosion resistance. For example, compared to AZ31 magnesium alloy, the hydrogen evolution rate of the two-stage sample decreases by a farceur to 1/2, and corrosion current density drops by a farceur to 10-3. The single stage sample has a crystalline/amorphous interlayer structure and ∼ 20 nm thickness, which could lead to a compressive residual stress for the single stage sample and even for the multi-stage coating. The compressive residual stress delays the germination of tiny defects. Furthermore, the multi-stage structure presents more interfaces that can impede longitudinal crack propagation and limit corrosion media diffusion, which contribute to the corrosion resistance. The work not only proposes a good protective coating for magnesium alloy but also presents a strategy for corrosion resistant coating design.