Tribological properties of Mn–TiN films and formation of graphite-like layers in physiological solution

Abstract

TiN film and Mn–TiN films containing 2.2, 5.6, and 10.6 at% Mn were deposited on appropriate substrates using a four-target unbalanced magnetron sputtering system. The Mn contents of films were adjusted by controlling the number of Ti–Mn alloy rods embedded in the titanium target. The effects of Mn doping on the microstructure, mechanical properties, and wear properties of TiN films were systematically investigated. A relatively loose columnar structure is observed in the TiN film, which is refined and densified by the incorporation of Mn. Mn doping improves the hardness, toughness, and adhesion performance of TiN films. The Mn–TiN films containing 2.2 and 5.6 at% Mn, in particular, exhibit superior mechanical properties. Moreover, the presence of Mn has a promoting effect on the wear of TiN films in both phosphate buffer (PB) and bovine serum albumin (BSA) solutions. The Mn ions released from Mn–TiN films during friction in a BSA solution promote the formation of protein deposits. The structures of protein molecules in these deposits denature under the frictional shear force of SiC balls during sliding tests, forming graphite-like layers on the friction interfaces. These layers act as a solid lubricant and improve the wear resistance of films.