Effect of soft substrate topography on tribological behavior of multifunctional DLC coatings

In this study, the influence of soft substrate surface finishing (5 distinct conditions) on tribological properties of hydrogenated amorphous carbon (a-C:H) films is investigated. Low carbon steel substrates were plasma-nitrided and DLC-coated in a single PECVD batch. Topographical evolution was investigated through white light interferometry (WLI) and scanning electron microscopy (SEM). The substrate topography leads to a negligible impact on bonding structure and mechanical properties of a-C:H films, which were analyzed by Raman spectroscopy (RS) and nano-indentation. The nitriding and deposition process resulted in two groups of samples regarding the topographic features: (A) Rough—Sq coated ≈ 0.17–0.23 µm; (B) Smooth—Sq coated ≈ 0.08–0.11 µm. Tribological performance of multifunctional coatings under incremental normal load reciprocating dry sliding tests in ambient air revealed friction coefficients of 0.09 (Rough) and 0.05 (Smooth). Wear scars were analyzed by WLI, SEM and RS. The results suggest that rougher substrates inhibit tribolayer formation and stability, leading to higher friction coefficients.