Tribological performance of laser peened Ti–6Al–4V Dharmesh Kumar a , Syed Nadeem Akhtar b , Anup Kumar Patel c , J. Ramkumar b , Kantesh Balani c,n a Materials Science Programme, Indian Institute of Technology Kanpur, Kanpur 208016, India b Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India c Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India article info Article history: Received 10 September 2014 Received in revised form 15 November 2014 Accepted 17 November 2014 Available online 25 November 2014 Keywords: Fretting Other materials (Ti–6Al–4V) Laser processing Profilometry Residual stress Stick-slip. abstract Ti–6Al–4V is a well-known metallic biomaterial used for implants, but its use is limited by its inferior hardness and tribological resistance in vivo. Laser peening (LP) is one potential means to enhance its tribological properties. LP induces surface residual compressive stresses due to plastic deformation caused by the propagation of a shock wave. Further, performing laser peening under water can enhance a material's hardness and wear resistance because it confines shock waves to the surface of the material. In the current research, the influence of an excimer laser (Kr–F, 248 nm) with varying fluence on the fretting behavior of Ti–6Al–4V was carried out. An optimized laser fluence of 100 J/cm 2 resulted in an increase in hardness by 28% in air and 35% in water confining media, respectively, when compared to that of an untreated Ti–6Al–4V substrate. It was observed that the residual compressive stresses from LP increased from 540 MPa in air to 604 MPa in water. Fretting wear against bearing steel type AISI E52100 shows a major wear reduction on LP Ti–6Al–4V samples as wear volume decreased from 1.211  10 3 mm 3 to either 0.139  10 3 mm 3 or to 0.106  10 3 mm 3 in samples peened in air and water, respectively. Frictional hysteresis data show that the dissipation energy loss for Ti–6Al–4V substrate from 11.412  10 4 J is decreased to 3.284  10 4 J for LP sample at 20 N load. Moreover, a considerable fall in contact diameter is observed from the non-processed surface (0.29  10 3 μm) to the LP sample (0.176  10 3 μm). Friction log plots indicate that wear mechanisms are mostly adhesion, abrasion and delamination. Enhanced tribological performance of LP Ti–6Al–4V was observed using LP in a water medium, and indicates potential improvements when the alloy is used in joint replacements. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Ti–6Al–4V is used in a variety of engineering applications due to its high strength, low density and high corrosion resistance, thus, withstanding dynamic loads and relative sliding, especially in turbine blades, aerospace vehicles and automotive components [1,2]. However, its potential applications are much broader, encompassing surgical tools and bio-implants. The only downside is its poor tribological characteristics such as release of metal debris due to friction during mobility, and release of metal ion that is toxic to human body [3]. Fretting wear occurs due to recurrent rubbing and slipping (in order of few micrometers) between two articulating surfaces [4]. Thus, in order to prevent the surface from degradation, surface modification techniques are mandated. Sur- face treatments that alter the microstructure of a surface include case hardening, shot peening, low plasticity burnishing, water jet peening and laser peening. Laser peening (LP) is a proven surface treatment process to enhance the service life of engineering components operating under dynamic loads [5]. This process induces residual compres- sive stresses deep into the material surfaces, typically 5–10 times deeper than conventional metal shot peening. Thus, the generated residual compressive stresses (in order of several hundreds of MPa) prohibit the initiation and propagation of cracks and enhance its service life. Laser peening has been particularly efficient in enhancing the performance of components of aircraft engine and turbines [6]. Since mechanical fatigue generally occurs by the progressive growth of a surface crack under cyclic loading, then if the stress experienced at the crack tip is below that of critical stress intensity factor, then crack will cease to grow further and fatigue failure will not occur [7]. Laser peening process usually induces compressive stresses in the grains, increases the dislocation density, and also pins the crack propagation and dislocation movement, which is very beneficial in increasing the life of critical service com- ponents [8]. The concept of laser shock propagation for properties enhance- ment was first used in early 1960s by Fairand and Clauer [9], Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/wear Wear http://dx.doi.org/10.1016/j.wear.2014.11.016 0043-1648/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ91 512 259 6194. E-mail address: kbalani@iitk.ac.in (K. Balani). Wear 322-323 (2015) 203–217