Tribological and mechanical properties of Ti/V/N-containing graded DLC coatings

This study investigates the structural, mechanical, and tribological properties of two novel functionally graded diamond-like carbon (DLC) coatings—Ti–TiC–TiVC–a:C and Ti–TiC–TiVC–TiVCN–a:C—deposited on AISI M2 tool steel via closed-field unbalanced magnetron sputtering. The coatings, with thicknesses of 1.5 µm and 1.7 µm respectively, were engineered to overcome the intrinsic challenges of DLC coatings, such as high residual stress and poor adhesion. A significant enhancement in microhardness was achieved, with values reaching 1300 HK₀.₀₁ (0.1 N) for the Ti–TiC–TiVC–a:C coating and 1425 HK₀.₀₁ (0.1 N) for the Ti–TiC–TiVC–TiVCN–a:C coating, substantially exceeding the substrate hardness of 800–850 HK₀.₀₁. Scratch testing revealed excellent adhesion, with critical load (Lc) values of 24 N and 21 N, indicating only a minor trade-off for the nitrogen-enriched variant. Both coatings exhibited an exceptionally low and stable friction coefficient of 0.09. Crucially, the incorporation of a nitrogen-rich TiVCN interlayer led to a remarkable 33% improvement in wear resistance, reducing the wear rate from 1.0 × 10 − 5 mm 3 /N·m to 6.7 × 10 − 6 mm 3 /N·m. These findings demonstrate that vanadium-based graded DLC systems, particularly those utilizing carbonitride phases, offer a superior balance of high hardness, exceptional wear resistance, and excellent lubricity, making them prime candidates for advanced tribological applications.