Coefficient of friction and wear of sputtered a-C thin coatings containing Mo

The paper reports on preparation of ~ 3000 nm thick a-C coatings containing Mo, interrelationships between their mechanical properties, a coefficient of friction μ and wear rate k and the effect of Mo content in the a-C coating on these interrelationships. The Mo-C coatings were prepared by sputtering using an unbalanced magnetron (UM) equipped with a graphite targets (∅ = 100 mm, 99.9% purity) fixed to the UM cathode with Mo ring of different inner diameter ∅_i. The content of Mo in the a-C coating was controlled by ∅_i. It is shown that μ and k of the coating strongly depend not only on its hardness H but also on its effective Young's modulus E^? = E/ (1 − ν²), the ratios H/E^?, H³/E^?2 and the elastic recovery W_e; here E is the Young's modulus and ν is the Poisson ratio. The ratio H³/E^?2 characterizes the resistance of coating to plastic deformation. Coatings with a low amount of Mo composed of nanograins of carbides dispersed in a-C matrix exhibit low values of μ ≈ 0.07 and k ≈ 10^− 7 mm³/Nm measured with WC ball at the rotation speed v = 0.05 m/s, total sliding length l = 1000 m and the load L = 2 N.