The Effect of Microstructure and Composition of Molybdenum and Tungsten-Doped Vacuum Ion-Plasma Carbon Coatings on Their Tribotechnical Properties under Dry Friction and Boundary Lubrication

The paper presents the results of a study of the chemical and phase composition, structure, physicomechanical, and tribological characteristics of two types of vacuum ion-plasma antifriction carbon coatings alloyed with molybdenum and tungsten, respectively. The first of these types of coatings has a highly oriented linear-chain structure; the second type is an amorphous hydrogenated carbon. The tribotechnical characteristics of the studied coatings were evaluated on a four-ball machine with a modernized friction unit and were carried out both under dry friction and under friction in the boundary lubrication mode in inactive (polyalphaolefin oil PAO-4), surface-active (PAO-4 + 1% by weight of oleic acid) and chemically active (the same oil + 2% by weight of DF-11 additive) lubricating environments. It was found that the coating with both “monocrystal” carbon and diamond-like carbon, both alloyed and unalloyed, significantly reduced friction losses and wear of the steel samples to which the coatings were applied, and alloying of these coatings reduced friction almost as much as the studied lubricants. Thus, under dry friction of a ball made of ShKh-15 steel on the cylindrical surfaces of rollers made of the same steel, the friction coefficient obtained was ~0.8; when a ball rubs against rollers coated with a molybdenum-doped “monocrystalline carbon” coating, the dry friction coefficient is ~0.7; additionally, in an inactive oil environment, this friction pair provides a friction coefficient of 0.12–0.14; and in a chemically active sulfur-containing oil environment, the friction coefficient decreases to 0.05. For a friction pair of steel –molybdenum-doped diamond-like coating, with boundary lubrication by a surface-active composition, the minimum friction coefficient is 0.09. Taking into account the results of the proposed study will allow optimizing the process of creating highly effective lubricants for heavily loaded friction units.