Investigation of surface treatments for galling protection of titanium alloys

A galling test has been developed in which two nominally identical crossed cylinders are slid over each other under a steadily increasing contact load . The test has been applied to samples of the titanium alloy Ti6Al4V with m odified surfaces. Loads up to 200 N were applied to cylinders of 6.35 nun i n diameter. Six different treatments were applied: (1-2) two variants of a novel commercial vapour phase treatment (IonSlip); (3) a PACVD diamond-like carbon (DLC) coating; (4-5) two different forms of PVD TiN coatings, one a rc-evaporated and the other electron beam-evaporated; and (6) a thermal oxi dation treatment which produced a rutile (TiO2) surface layer. Specimens of the un-coated titanium alloy were also examined as controls. The carbon-ba sed coatings, (DLC and standard IonSlip), provided the best performance, wi th both giving low friction coefficients and galling protection at very hig h contact loads. Thermal oxidation also provided excellent protection again st galling but with a friction coefficient not so low as the carbon-based c oatings. Electron-beam evaporated TiN provided low friction and adequate ga lling protection at low loads but failed to protect at high contact loads. (C) 2001 Elsevier Science B.V. All tights reserved.