Rolling contact properties of ta-C coated low alloy steel

Their high hardness and good thermal and chemical stability together with low friction and high sliding wear resistance make diamond-like carbon (DLC) coatings one of the best candidates for improving the tribological properties and durability of machine components. However, when applied on soft materials like low alloy steels, very thin and brittle DLC coatings have very little to offer. On the other hand, surface engineering combining thermo-chemical treatment of the steel substrate and deposition of a hard wear resistant coating has been found to greatly improve the sliding wear properties of contact surfaces. However, in the majority of machine element applications appropriate rolling and sliding properties are required simultaneously. The aim of the present work was to determine the load-carrying capacity and durability of tetrahedral amorphous carbon (ta-C) coated low alloy steel under rolling conditions. Samples made of AISI 4140 steel were first plasma nitrided and then coated with a hydrogen-free hard carbon coating. Results of the rolling tests, performed under various conditions, show that by proper treatment of the substrate material not only the sliding but also the rolling properties of ta-C coated low alloy steel can be greatly improved.