Influence of carbon concentration on the electrochemical behavior of CrCN coatings in simulated body fluid

• CrCN coatings with diverse carbon concentrations were deposited on 316 L disks.
• All coated 316 L performed better corrosion resistance than uncoated 316 L in SBF.
• CrCN coating (15.4 at.% C) with N–C bond alone was a favorable candidate.
• Protective effect of CrCN (52.6 and 75.0 at.% C) was degraded by unstable NC bond.

CrCN coatings with various carbon contents were deposited on 316 L stainless steel disks by unbalanced magnetron sputtering via adjusting carbon target current, and their relevant microstructure was characterized by Raman spectrum and X-ray photoelectron spectroscopy, respectively. The influence of carbon content on the electrochemical properties of CrCN coatings in simulated body fluid (SBF) was investigated using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. It turned out that the CrCN-coated 316 L disks performed better electrochemical properties than uncoated 316 L disk. All CrCN coatings contained a-CNx, but the bonding structure converted from N–C bonds to NC bonds as carbon content increased. As a result, the CrCN coatings (52.6–75.0 at.% C) with NC bonds were prone to be easily degraded by breakage of π bond. In contrast, the CrCN coatings (15.4 at.% C) with N–C bond alone exhibited relatively higher charge transfer resistance (Rct), and was able to prolong the longevity of prosthesis.