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

The paper reports on preparation of similar to 3000 nm thick a-C coatings containing Mo, interrelationships between their mechanical properties, a coefficient of friction mu 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 ((empty set) = 100 mm, 99.9% purity) fixed to the UM cathode with Mo ring of different inner diameter (empty set)(i). The content of Mo in the a-C coating was controlled by (empty set)(i). It is shown that mu and k of the coating strongly depend not only on its hardness H but also on its effective Young's modulus E*= E/(1 - nu(2)), the ratios H/E*, H-3/E*(2) and the elastic recovery W-e; here E is the Young's modulus and v is the Poisson ratio. The ratio H-3/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 mu approximate to 0.07 and k approximate to 10(-7) mm(3)/Nm measured with WC ball at the rotation speed v = 0.05 m/s, total sliding length 1 = 1000 m and the load L = 2 N. (C) 2010 Elsevier B.V. All rights reserved.