Structures, electrochemical properties and corrosion mechanisms of TiAlCr(C)N/TiAlN/TiN coatings by DFT calculations

Element additions in ceramic coatings played a positive role in electrochemical corrosion process, and Cr and C were doped into TiAlN coating by cathode arc ion plating. The effects of Cr and C additions on the structures and electrochemical properties of TiAlN coatings in 3.5% NaCl solution were comparatively investigated, and the corrosion mechanisms were discussed with the density functional theory calculation. The results show that the particle size of TiAlCrN/ and TiAlCN/TiAlN/TiN coatings are 31.6 and 25.7 nm, respectively, and the corresponding bonding strength is 16.18 and 37.93 N, respectively. The corrosion resistance of TiAlCrN/TiAlN/TiN coating is higher compared with the TiAlCN/TiAlN/TiN coating, which is attributed to the stronger oxidation reactions of TiAlCrN/TiAlN/TiN coating. The donor density of passive film on the TiAlCrN/TiAlN/TiN coating is lower than that on the TiAlCN/TiAlN/TiN coating, showing the minor susceptibility of TiAlCrN/TiAlN/TiN coating to corrosion. Moreover, the band gap and DOS of Cr2N and Cr2O3 on the TiAlCrN/TiAlN/TiN coating are larger than those of Al3C4 on the TiAlCN/TiAlN/TiN coating, presenting the stronger corrosion resistance.