Tribological and Wear Properties of DLC Composite Coatings with Different Ratios of CrN/Cr2N

CrN/DLC composited coatings were deposited on 431 stainless steel, and their structure was analyzed, with particular emphasis on the influence of CrN content on the coating properties. X-ray photoelectron spectroscopy (XPS), nanoindentation testing, scratch testing, and reciprocating tribometry were employed to characterize the chemical composition, mechanical properties, adhesion strength, and tribological performance of the coatings, respectively. Structural analysis indicates that when the ratio of CrN/Cr2N is relatively low (<1), a high content of chromium dinitride (Cr2N) is formed in the interlayers, resulting in a porous and loose coating structure. When the ratio achieves 1:1, an optimal balance, with the CrN content reaching a maximum of 21.04% and the Cr2N content decreasing to a minimum of 20.68%, the densification degree of the coatings is increased, the coating adhesion strength is improved to 11.87 N. Meanwhile, the enhanced formation of the CrN phase improves the hardness to 12.27 GPa. Tribological test results demonstrate that when the ratio is approximately 1:1, the coating exhibits the lowest friction coefficients under dry sliding, deionized water, and artificial seawater conditions (0.0932, 0.1409, and 0.1021, respectively), as well as the minimum wear rates. With the decrease in CrN content of the coatings, the interfacial mismatch degree of the coatings is aggravated, which leads to not only more interfacial defects but also a relatively loose structure, as well as a decrease in the bonding strength (6.81 N), hardness (5.22 GPa), and deformation resistance. Therefore, an excessive Cr2N phase may degrade the hardness-to-elastic modulus ratio (H/E) of the coatings by increasing interfacial mismatch and reducing structural compactness.