Influence of individual Cr–C layer thickness on structural and tribological properties of multilayered Cr–C/a-C:Cr thin films

Multilayered Cr–C/a-C:Cr thin films were prepared by using a hybrid technique of combined vacuum cathodic arc/magnetron sputtering/ion beam deposition. The multilayered films consisted of a dense gradient base layer and 10 bi-layers of Cr–C (chromium matrix containing some carbon) and a-C:Cr (amorphous carbon matrix containing a small amount of chromium). The thickness of individual a-C:Cr layer was kept constant at about 18.5 nm, while that of individual Cr–C layer varied from 11.1 to 55.1 nm. It was found that an increase of the individual Cr–C layer thickness from 11.1 to 40 nm resulted in increase in material nanohardness from 7.6 to 13.6 GPa and Young's modulus from 107 to 164.8 GPa. However, a further increase in the individual Cr–C layer thickness to 55.1 nm led to decrease in nanohardness to 9.5 GPa and Young's modulus to 142.4 GPa. The scratch tests indicate that the adhesion strengths between the films and substrates are dramatically improved through the multilayered structure, acquiring critical loads exceeding 80 N. The results of pin-on-disk tests show that the lowest wear rate 1.35 × 10− 6 mm3/Nm was achieved from the coated sample with the individual Cr–C layer thickness of about 40 nm.