Influence of Interstitial Oxygen on the Tribology of Ti6Al4V
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ORIGINAL PAPER
Influence of Interstitial Oxygen on the Tribology of Ti6Al4V Daniel Kümmel1,3 · Johannes Schneider1,3 · Peter Gumbsch1,2,3 Received: 24 April 2020 / Accepted: 4 August 2020 © The Author(s) 2020
Abstract Titanium alloys are used for their good mechanical and corrosion properties, but generally experience poor wear behavior. This can effectively be counteracted by a thermal oxidation treatment, reducing wear significantly. Employing a special sample preparation, we study the transition of tribological properties between thermally oxidized and bulk Ti6Al4V on a single sample. While oxygen signal intensity and hardness followed an exponential decay from the surface to bulk material, tribological results showed a step-like transition from low to high friction and wear with increasing distance from the surface. Low wear was associated with minor abrasive marks, whereas high wear showed as severe adhesive material transfer onto the steel counter body. Besides the mechanical property of hardness, also a change in fracture behavior by interstitial oxygen could influence the observed tribological behavior. Keywords Adhesive wear · Aviation · Boundary lubrication · EDS · Surface modification · Titanium
1 Introduction Titanium alloys are heavily used for their high specific strength and good corrosion resistance. Their high strengthto-weight ratio makes them desirable materials especially in aerospace industry [1]. Their excellent corrosion resistance yields good biocompatibility which, together with high strength, makes them appicable in biomedical industry [2]. The α/β-alloy Ti6Al4V is by far the most commonly used titanium alloy [3]. A major drawback of titanium alloys are the notoriously poor tribological properties like high, unsteady friction [4] and low wear resistance [5]. In most cases, distinct signs of adhesive wear are observed, like deep craters and material transfer to the counter body, which result in high wear rates [6, 7]. In many applications, the use of titanium alloys is therefore considered to be restricted to non-tribological parts [8]. In order to overcome this limitation, many different methods of surface engineering have been used on titanium alloys in order to improve their * Johannes Schneider [email protected] 1
Institute for Applied Materials IAM, Karlsruhe Institute of Technology KIT, Karlsruhe, Germany
2
Fraunhofer Institute for Mechanics of Materials IWM, Freiburg, Germany
3
MicroTribology Center μTC, Karlsruhe, Germany
tribological properties. For instance, mechanical treatments like shot peening, burnishing, laser peening have been used in order to induce residual compressive stresses or nanocrystalline surface layers [9–12]. Furthermore, different types of hard coatings like Cr, CrN, NiP, TiN or DLC [5, 9, 13–15] or soft coatings like solid lubricants [5, 16] have been applied in order to reduce wear on titanium alloys. Several methods of introducing interstitial atoms were successful in reducing wear on titanium alloys, such as ion implantation [1
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