Electrochemical performance and corrosion mechanism of Cr-DLC coating on nitrided Ti6Al4V alloy by magnetron sputtering

A Cr-DLC coating was deposited on nitrided Ti6Al4V alloy (TA) by magnetron sputtering (MS) using CrN as an interlayer. The characterization processes of obtained coating were performed on scanning electron microscopy (SEM), energy dispersive spectroscope (EDS), X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM), and the hardness and bonding strength were also measured by nanoindentation and scratch testers. The electrochemical corrosion performances of TA, nitrided TA and Cr-DLC coating in 3.5% NaCl solution were systematically investigated using an electrochemical workstation, and the corrosion mechanisms were discussed in detail. The results show that the amorphous carbon atoms are uniformly distributed on the in-situ grown Cr-DLC coating, and the CrN interlayer plays an important connection role between the Cr-DLC coating and the nitrided TA. After the electrochemical corrosion test, the O mass fraction on the Cr-DLC coating is lower than those on the TA and nitrided TA, and the nitrided TA is effectively protected from electrochemical corrosion. The Cr-DLC coating presents the smallest corrosion current density icorr and the largest polarization resistance Rp among the TA, nitrided TA and Cr-DLC coating, showing the outstanding electrochemical corrosion resistance. Meanwhile, the capacitive arc radius, impedance |Z| and phase angle of Cr-DLC coating are also the maximum, exhibiting that its electrochemical corrosion resistance is higher than the TA and nitrided TA.