Wear 258 (2005) 1348–1356 Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces  Jun Qu a,∗ , Peter J. Blau a , Thomas R. Watkins a , Odis B. Cavin b , Nagraj S. Kulkarni a a Metals and Ceramics Division, Oak Ridge National Laboratory, P. O. Box 2008, MS 6063, Oak Ridge, USA b University of Tennessee, Knoxville, USA Received 11 July 2003; received in revised form 21 September 2004; accepted 23 September 2004 Available online 11 November 2004 Abstract Recent advances in lower-cost processing of titanium, coupled with its potential use as a light weight material in engines and brakes has renewed interest in the tribological behavior of titanium alloys. To help establish a baseline for further studies on the tribology of titanium against various classes of counterface materials, pin-on-disk sliding friction and wear experiments were conducted on two different titanium alloys (Ti–6Al–4V and Ti–6Al–2Sn–4Zr–2Mo). Disks of these alloys were slid against fixed bearing balls composed of 440C stainless steel, silicon nitride, alumina, and polytetrafluoroethylene (PTFE) at two speeds: 0.3 and 1.0 m/s. The friction coefficient and wear rate were lower at the higher sliding speed. Ceramic sliders suffered unexpectedly higher wear than the steel slider. The wear rates, ranked from the highest to the lowest, were alumina, silicon nitride, and steel, respectively. This trend is inversely related to their hardness, but corresponds to their relative fracture toughness. Comparative tests on a Type 304 stainless steel disk supported the fracture toughness dependency. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses confirmed the tendency of Ti alloys to transfer material to their counterfaces and suggested possible tribochemical reactions between the ceramic sliders and Ti alloy disks. These reaction products, which adhere to the ceramic sliders, may degrade the mechanical properties of the contact areas and result in high wear. The tribochemical reactions along with the fracture toughness dependency helped explain the high wear on the ceramic sliders. © 2004 Elsevier B.V. All rights reserved. Keywords: Titanium; Ceramics; Material transfer; Tribochemical reaction 1. Introduction In comparison to light weight alloys based on aluminum and magnesium, titanium alloys present interesting possibil- ities as tribomaterials, but they have not been widely inves- tigated as bearing materials. They are harder and stiffer than Mg and Al alloys, and they resist exposure to heat and aque- ous corrosion much better. Like Al and Mg, their high affinity  Research sponsored by the U.S. Department of Energy, Assistant Secre- tary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies, as part of the High Strength Weight Reduction Materials Program, under contract DE-AC05-00OR22725 with UT-Battelle, LLC. ∗ Corresponding author. Tel.: +1 865 574 4560; fax: +1 865 574 6918. E-mail address: qujn@ornl.gov (J. Qu). for oxygen results in the formation of an adherent surface ox- ide, but sub-stoichiometric TiO 2 can act as a solid lubricant. A great deal is known about the physical metallurgy, heat treatment, and mechanical properties of titanium alloys, thanks to extensive aerospace-related research and develop- ment. Tribological concerns for Ti in aerospace components have focused mainly on their fretting behavior, leading to re- search on surface treatments like ion implantation and solid film lubrication [1,2]. Needs in the chemical process industry motivated a 1991 study of the galling and sliding wear be- havior of commercial-purity Ti and alloy Ti–6Al–4V [3]. In that investigation, the best wear and friction results for Ti al- loys were obtained for anodized counter-surfaces coated with MoS 2 solid-film or with polytetrafluoroethylene (PTFE), but the abrasion resistance was poor. Relatively few additional 0043-1648/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2004.09.062