Enhanced Corrosion Resistance of PVD-CrN Coatings by ALD Sealing Layers

Multilayered hard coatings with a CrN matrix and an Al₂O₃, TiO₂, or nanolaminate-Al₂O₃/TiO₂ sealing layer were designed by a hybrid deposition process combined with physical vapor deposition (PVD) and atomic layer deposition (ALD). The strategy was to utilize ALD thin films as pinhole-free barriers to seal the intrinsic defects to protect the CrN matrix. The influences of the different sealing layers added in the coatings on the microstructure, surface roughness, and corrosion behaviors were investigated. The results indicated that the sealing layer added by ALD significantly decreased the average grain size and improved the corrosion resistance of the CrN coatings. The insertion of the nanolaminate-Al₂O₃/TiO₂ sealing layers resulted in a further increase in corrosion resistance, which was attributed to the synergistic effect of Al₂O₃ and TiO₂, both acting as excellent passivation barriers to the diffusion of corrosive substances.