Optimization of DLC coating structure for fatigue resistance improvement

Diamond-like carbon (DLC) coatings are extensively employed across diverse industrial sectors due to their excellent tribological performance, combining low friction and high wear resistance. However, their long-term mechanical reliability, particularly in terms of fatigue resistance, remains a critical challenge. The endurance of DLC-based films under cyclic loadings, very often in association with high-speed sliding or impacts, depends upon multiple factors, including coating architecture and layer chemical composition, thickness and other physical properties. Assessing fatigue resistance in thin films is inherently complex, with traditional laboratory testing methods offering limited insight. Moreover, the mechanical characteristics of the substrate, especially hardness and surface finish, significantly influence coating dynamic performance. The aim of this work is to investigate interactions playing a role in fatigue behaviour for different DLC-based coating solutions, resulting in a benchmark useful as a starting point for an improved design of high-performance film for mechanical components. Various substrate materials, commonly used in engineering applications, were selected: 1.3343 tool steel (both hardened and plasma-nitrided), 17-4 PH stainless steel, and Ti6Al4V titanium alloy. A range of DLC-based coatings, both established industrial solutions and novel experimental formulations, were deposited on these materials samples with different coating techniques, including conventional PACVD, microwave-enhanced deposition and UBM sputtering. The deposition parameters were systematically varied to investigate their influence on structural integrity and fatigue performance. Comprehensive laboratory analyses, supported by extensive nano-impact testing, revealed key insights into the behaviour of each coating-substrate system. The results lead to the identification of an optimized DLC coating architecture, capable of significantly enhancing fatigue resistance through tailored multilayer design and process refinement.