Microstructure, mechanical and tribological properties of multilayer Ti-DLC thick films on Al alloys by filtered cathodic vacuum arc technology

Low hardness and poor wear resistance are major limitations of Al alloys, which hinder their application in several fields, especially automotive moving parts. DLC can effectively improve hardness and wear resistance of Al alloys, but high residual stress and poor adhesion limit the film thickness. Multilayer thick films (~10 μm) composed of alternating Ti and Ti-DLC layers were successfully deposited on Al alloys. The influence of Ti content on the microstructure, mechanical and tribological properties of the film was emphasized. As the Ti content decreased from 10.42 to 1.35 at.%, the microstructure evolved from a polycrystalline composite film to a nanocrystalline composite film, and then to an amorphous film. The mechanical and tribological properties of the film depended on the microstructure. The amorphous composite film (Ti >6.06 at.%) exhibited better wear resistance than the polycrystalline composite film (Ti <6.06 at.%) due to the higher H/E^⁎ (>0.1), H³/E^⁎2 (>0.2) and elastic recovery (>60%). When the doped Ti content was 6.06 at.%, the nanocrystalline composite multilayer film showed superior comprehensive performance of high hardness (~23 GPa), high elastic recovery (~69%), low friction coefficient (~0.13) and low wear rate (1.0 × 10⁻⁷ mm³/Nm).