Applied Surface Science 270 (2013) 58–63 Contents lists available at SciVerse ScienceDirect Applied Surface Science jou rn al hom epa g e: www.elsevier.com/locate/apsusc The effect of multi-scale laser textured surface on lubrication regime Dawit Zenebe Segu a , Si Geun Choi a , Jae hyouk Choi b , Seock Sam Kim a,∗ a Department of Mechanical Engineering, Graduate School, Kyungpook National University, Daegu 702-701, South Korea b Department of Architectural Engineering, Graduate School, Chosun University, Gwangju 501-759, South Korea a r t i c l e i n f o Article history: Received 25 August 2012 Received in revised form 19 November 2012 Accepted 12 December 2012 Available online 7 January 2013 Keywords: Laser surface texture AISI 52100 steel multi-scale texturing Friction Lubrication regime a b s t r a c t Laser surface texturing (LST) is a surface engineering process used to improve tribological characteristics of materials by creating patterned microstructures on the mechanical contact surface. In LST technology, a pulsated laser beam is used to create arranged dimples on surface by a material ablation process, which can improve load capacity, wear resistances, lubrication lifetime, and reduce friction coefficients. In the present study, the effect of multi-scale LST on lubricant regime was investigated. A pulsed Nd:YAG laser was applied on steel (AISI 52100) to create arranged dimples. To optimize the surface texturing effect on friction, multi-scale texture dimples with some specific formula arrays were fabricated by laser ablation process by combining circles and ellipses. The tribological testing of multi-scale textured surface was performed by a flat-on-flat unidirectional tribometer under lubrication, and the results compared with that of untextured surface. Through an increase in sliding speed and dimple depth the beneficial effect of multi-scale LST performance was achieved. The multi-scale textured surface had lower friction coefficient performance than the untextured surface due to hydrodynamic lubrication effect. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The complexity of the tribological properties of materials and the economic aspects of friction and wear justify an increasing research effort [1]. There is an increasing demand to reduce and control friction and wear in order to extend the lifetime of mechan- ical systems, to improve their efficiency and reliability, to conserve scarce material resources and energy, and to improve safety [1,2]. This enhanced the efforts to investigate new or advanced materi- als and surface topography and texture design that improve the tribological performance of friction surface. The laser surface texturing (LST) is a process used to improve tribological characteristics of materials by creating patterned microstructures on the mechanical contact surface. In LST tech- nology, a pulsated laser beam is used to create patterned microstructures on surface by a material ablation process, which can improve anti-seizing ability by reserving lubricant, trapping wear debris to prevent further abrasive wear, decreasing the contact area to reduce adhesion, and generating hydrodynamic pressure to improve additional lift. The first use of surface irreg- ularities to improve tribological properties was discussed in the 1960s and implemented in several manufacturing techniques [3]. Since then, various design and texture fabrication techniques have been employed, such as ion beam texturing, etching techniques ∗ Corresponding author. Tel.: +82 53 950 5577; fax: +82 53 950 6588. E-mail address: sskim@knu.ac.kr (S.S. Kim). and machining and laser texture. The LST technique seems to be the most advanced of all known methods of surface textur- ing for tribological application. Different patterns have also been used; the common microstructures being linear grooves, crossed grooves, and circular dimple-like depressions [4]. These patterns are useful for effective lubrication between contact surfaces by providing micro-hydrodynamic bearing, lubricant reservoirs and traps for wear debris in both lubricated and non-lubricated appli- cation, which protect the surface from scratching. In cases of mixed lubrication, micro-scale asperities can create an asymmetric oil pressure distribution that results in hydrodynamic lift that can change the balance between hydrodynamic and boundary lubri- cation, reducing the amount of asperity contact that takes place, and thus reducing both friction and wear. Also, when contact does not occur (hydrodynamic lubrication), dimples may increase the oil film thickness, thus reducing shear within the oil and hydro- dynamic friction. In recent years, surface texturing has been successfully used in many applications to improve the tribological properties of slid- ing surfaces, such as golf ball, engine cylinder, modern magnetic storage device, sliding bearing and mechanical seal, and slider and disc of hard disc driver [5]. A report by Etsion [6] on mechani- cal seals with regular micro-surface texture showed that the seal performance was substantially improved when evenly distributed hemispherical micro-dimples are present on one of the mating seal faces. On the other hand, the effect of partial LST on piston rings was evaluated for friction reduction, and the results indicated that the friction coefficient was reduced up to 25% with partial LST 0169-4332/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2012.12.068