Tribology Online, 7, 2 (2012) 87-95. ISSN 1881-2198 DOI 10.2474/trol.7.87 Copyright © 2012 Japanese Society of Tribologists 87 Article Dry Sliding Friction and Wear Behaviour of Titanium Alloy (Ti-6Al-4V) Mukund Dutt Sharma and Rakesh Sehgal* Department of Mechanical Engineering, National Institute of Technology Hamirpur 177005 (H.P.), India *Corresponding author: rakeshsehgal.nitham@gmail.com ( Manuscript received 13 September 2011; accepted 26 March 2012; published 30 May 2012 ) Friction and wear are the most commonly encountered industrial problems leading to the replacement of components and assemblies in engineering. There have been great advances in the development of aerospace technology because of the use of titanium alloys. Titanium alloys have wide range of applications for which they have received considerable interest recently because they show an astonishing range of mechanical properties. The present investigation covers the study of dry sliding friction and wear of the Ti6Al4V alloy, which alone covers about 50% of the total world production of titanium alloys. The main objective of this study is to investigate the dry sliding friction and wear behaviour of titanium alloy (Ti-6Al-4V) sliding against EN31 steel. The results show that the wear rate of the Ti6Al4V alloy decreases with increasing sliding velocity and decreasing normal load with few exceptions thus showing typical transition characteristics. The average coefficient of friction decreases as the normal load increases with few exceptions. Also the average coefficient of friction increases as the sliding distance increases for all loads and sliding velocities. The average length of biggest, medium and smallest wear debris was found to be 1.026 µm, 0.711 µm and 0.401 µm respectively. Keywords: friction, wear, Ti-6Al-4V alloy, dry sliding 1. Introduction The primary attributes that make titanium an attractive material include high specific strength, easy formability, fatigue resistance and excellent corrosion resistance. This also explains their preferential use in the aerospace applications (like rocket engine parts, fuel tank, gas bottles), the chemical industry, medical engineering etc. It is also used in the airframe structures, such as landing-gear beams, hydraulic tubing, wing boxes, spacers, bolts, etc. Titanium alloys are used in fan-jet engines for which large front fans are required. An excellent strength-to-weight ratio of titanium along with the metallurgical stability at high temperatures and low creep rates make it favourable for jet engine components like blades and discs in the low and intermediate sections of compressors. Another important area of application of titanium alloys is chemical and general engineering. The outstanding corrosion resistance of titanium in many environments is the prime reason for its use in these industries. For low-stress applications, commercially pure (CP) titanium is generally used, and for high strength applications Ti-6Al-4V or Ti-13Nb-13Zr alloys are used [1]. Sliding wear processes of ductile materials are often accompanied by severe plastic deformation [2]. A characteristic feature of the sliding wear of metals is the occurrence of transitions in the rate of material loss as a function of sliding velocity, applied load, and ambient temperature. In the mild (oxidational) wear regime, the sliding metals are separated by thin oxide films and direct metallic contact occurs only occasionally. Wear rates are low and the debris formed by the wear process is typically finely divided and consists of a mixture of metallic oxides. Mild wear is generally associated with the low loads and sliding velocities, although a severe form of oxidational wear can occur at high sliding velocities and low loads where high interfacial temperatures result in rapid oxide film growth [3]. A brief literature review related to dry sliding friction and wear characteristics of titanium alloys and their worn surface analysis is presented as follows: Bare titanium galls and seizes readily when in sliding contact with itself and most other metals [4]. Titanium, although a hexagonal metal, exhibits relatively high friction. The coefficient of friction for titanium sliding on titanium and on 440-C stainless steel decreased with increasing sliding velocity or interface temperature apparently because of an increase in the c/a lattice ratio as well as