DLC Coatings for Manufacturing Applications: Effects of Coating Structure on Mechanical and Tribological Performance

Adhesion strength, toughness, and resistance to frictional heating are critical characteristics for suppressing premature coating delamination and protecting the substrate from plastic deformation. This study investigates the synergistic role of intermediate adhesion-promoting layers on the mechanical and tribological performance of diamond-like carbon (DLC) coatings deposited on tool steel substrates via high-power impulse magnetron sputtering (HiPIMS). Nanoindentation and micro-scratch testing were conducted to evaluate single-layer TiAlN, single-layer DLC, and multilayer DLC/TiAlN coating architectures. Owing to the TiAlN interlayer beneath the DLC topcoat, the multilayer DLC/TiAlN system demonstrated superior composite hardness and interfacial adhesion strength. Microstructural characterization via SEM-EDS and Raman spectroscopy confirmed that a dense, columnar TiAlN interlayer with a high aluminum concentration provided vital load-bearing capacity for the overlying DLC film. During dry CNC turning tests on aluminum and steel alloys, the multilayer DLC/TiAlN coating exhibited the lowest cutting forces, cutting temperatures, and surface roughness. The architecture effectively suppressed flank and crater wear, which reduced the chip compression ratio and mitigated plastic shear strain at the tool–chip interface. This synergistic interaction within the DLC/TiAlN coating system minimizes tribological degradation, demonstrating high potential for demanding machining applications.