MaterialsScience and Engineering, A 115 (1989) 285-290 285 Friction Behavior and Debris Formation of Titanium-implanted 52100 Steel* S. FAYEULLEt Geo-Centers, Inc., 10903 Indian HeadHwy, Ft. Washington,MD 20744(U.S.A.) I. L. SINGER Code 6170. U.S. NavalResearch Laboratory, Washington DC 20375(U.S.A.) (Received September 16, 1988) Abstract The friction and wear behavior of titanium- implanted bearing steel (AIS1-52100) has been shown to depend critically on the near-surface composition, as determined by the implantation conditions. Friction, in turn, is believed to be con- trolled by wear debris, which have been found to consist mainly of oxides. In order to investigate the role of oxides, transfer films formed on non- implanted, titanium-implanted and oxidized sub- strates have been characterized by transmission electron microscopy and by Auger spectroscopy. Wear debris" contained mainly iron oxides and tita- nium oxides" and, occasionally, metallic iron. A mixture of Fe20~ + Ti203 was obtained from a Ti +- implanted surface. Fe~O 4 debris also developed in non-implanted substrates, but not in titanium- implanted substrates. The morphology of wear debris was highly dependent on the implantation conditions. Very thin flake debris were seen after Ti + and (Ti + + C +) implantation (and on TiC- coated steel) and are associated with low friction coefficients. Spherical debris were formed from non-implanted substrates and oxidized implanted substrates. Friction coefficients and wear behavior will be discussed in terms of chemistry of debris, adhesion between surface and debris, and the tribomechanical behavior of superficial layers. 1. Introduction Titanium implantation into steels, under special processing conditions, can produce an *Paper presented at the Sixth International Conference on Surface Modification of Metals by Ion Beams, Riva del Garda, Italy, September 12-16, 1988. tVisiting Scientist at NRL from Laboratoire de Metal- lurgie UA CNRS 447; Ecole Centrale de Lyon BP 63,69131 Ecully Cedex (France). unusually low friction surface with very low wear [1-5]. Singer has shown that the low friction on these optimally processed surfaces of type 52100 steel correlates with the presence of a high carbon concentration at the oxide-metal interface [6, 7], brought about by vacuum carburization during implantation [8]. Earlier studies revealed that insufficient carbon at the surface led to adhesive- type wear and high friction [2]. Recent studies have indicated that oxidation of these low friction surfaces leads to higher friction, without loss of the titanium-implanted layer [9]. In this paper we attempt to explain the role of the vacuum-carburized layer in the origins of low friction. We do this by determining the composi- tion and structure of debris formed during low and high friction sliding contact and identifying the wear modes that produce the debris. 2. Experimental details Disks of hardened 52100 steel were polished and implanted in NRL's modified Varian Extrion implanter. During implantation, disks were kept near room temperature owing to a water-cooled holder. The target chamber was cryogenically pumped to a base pressure of 5 × 10 -7 Torr. Samples were implanted with a 4STi+ beam (at current densities of 10-20 ~A cm 2) to a fluence of 5 × 1017 Ti cm -2 at an energy of 190 keV. One Ti+-implanted sample was also implanted with carbon (3 × 1017 C cm -2 at 50 keV) and another was oxidized at 300 °C for 1 h. Friction measurements were carried out in air (30% relative humidity, room temperature) on a Bowden-Leben type tester (sliding speed, 0.1 mm s -1) or on a pin-on-disk machine (sliding speed 8 mm s-l). Bowden-Leben tests con- sisted of repeated, unidirectional sliding on a 0921-5093/89/$3.50 © Elsevier Sequoia/Printed in The Netherlands