Mechanical and tribological properties of a-C/a-C:Ti multilayer films with various bilayer periods

• a-C/a-C:Ti multilayers with various bilayer periods were prepared.
• Nanocrystalline TiCs were confirmed in the a-C:Ti layer and at the interface.
• These multilayers show fine ability to comply with substrate deformation.
• The multilayer with a bilayer period of 12 nm exhibits the best properties.

Thick a-C/a-C:Ti multilayer films with bilayer periods of 12–70 nm were deposited on Ti6Al4V alloy substrate by means of closed field unbalance magnetron sputtering. The morphology and microstructure of the multilayer films were investigated by scanning electron microscopy, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Nanocrystalline TiC was distributed in the a-C:Ti layer and at the interface between the two adjacent layers. The mechanical and tribological properties were evaluated by Rockwell and scratch tests, a nanoindentor and a ball-on-disk tribometer. The multilayer film with a bilayer period of 12 nm showed the highest adhesion strength, hardness (26 GPa) and elastic modulus (232 GPa); it also had the lowest average coefficient of friction (0.09) and a wear rate of 8.06 × 10− 17 m3 N− 1 m− 1.