The properties of a-C:H(Al, W) films prepared by medium frequency magnetron sputtering

A series of W and Al co-doped hydrogenated amorphous carbon flms (a-C:H(Al, W) films) were deposited on n(100) Si substrates by medium frequency magnetron sputtering W-Al composite target (area ratio 1:1) in argon and methane gas mixture atmosphere. The effect of CH₄ flow rate on the composition, structure and surface morphology of films were analyzed, and the mechanical and tribological properties of films were also characterized. The results demonstrate that with the increase of CH₄ flow rate, the contents of carbon of films increased while the contents of W and Al decreased gradually, and the metallic target could be poisoned due to the overhigh CH₄ flow rate. The contents of sp²C and sp³C could be controlled by the W, Al and H implantation. The surfaces of all films were rather smooth, with the Root Mean Square surface roughness between 0.386 nm and 0.480 nm. The nano-hardness (H) and elastic modulus (E) of films were between 9.98 GPa and 11.37 GPa, 71GPa and 93.36 GPa, respectively. And all samples exhibited elastic recovery rate higher than 70%. The film containing 3.74% of W and 2.37% of Al showed favorable antifriction and wear-resistant properties in ambient air with a H/E ratio of 0.141 and a H³/E² ratio of 0.198. The good tribological property of film can be attributed to moderate ratio of sp³C/sp²C, excellent elastic deformation property and the transfer layer on counter body.