Wear 259 (2005) 703–707 Behavior of fullerene-like WS 2 nanoparticles under severe contact conditions L. Rapoport a, ∗ , O. Nepomnyashchy a , I. Lapsker a , A. Verdyan a , A. Moshkovich a , Y. Feldman b , R. Tenne a, b a Department of Science, Holon Academic Institute of Technology, 52 Golomb St., P.O. Box 305, Holon 58102, Israel b Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel Received 15 July 2004; received in revised form 2 January 2005; accepted 7 January 2005 Available online 5 February 2005 Abstract Fullerene-like WS 2 (MoS 2 ) nanoparticles (IF) have been studied in the past. It was shown that the IF nanopaticles appear to form a protective film allowing increased load capacity of the rubbed pairs under mixed lubrication. The main objective of the present work is to evaluate the behavior of the IF nanoparticles under severe contact conditions—the transition to seizure. The effect of the IF nanoparticles burnished to porous alumina matrix on friction and wear of alumina-Si 3 N 4 pair under high contact pressure is also considered. It was shown that when the gap between the contact surfaces is smaller than the size of the IF nanoparticles, there is no effect of the nanopaprticles on the friction force. With load increasing, the IF nanoparticles penetrate into the interface, protecting the rubbed surfaces from a direct contact and thus increase the critical point of transition to seizure. Burnishing of the porous alumina surfaces by the IF solid lubricant nanoparticles provides very low friction coefficient and wear loss under high contact pressure. The IF-WS 2 nanoparticles are found to be preserved in the rough summits, fill the valleys, and the pores of the sintered alumina and thus limit the straight contact between the ceramic surfaces. Although the external sheets of the outermost layers of the IF-WS 2 nanoparticles were peeled-off, the pristine IF nanoparticles remain in the valleys and pores of the alumina supplying the solid lubricant sheets to the contact area during a long-term test. © 2005 Elsevier B.V. All rights reserved. Keywords: Friction and wear; Solid lubricant; Seizure; Nanoparticle 1. Introduction Fullerene-like WS 2 (MoS 2 ) nanoparticles (IF) have been studied in the past [1–3]. Their efficacy as additives for lubri- cation fluids was demonstrated in a series of tests [4]. These experiments showed that the IF added to oil possess lubricat- ing properties superior to those of 2H platelets in a definite range of operating conditions [5]. The tribological properties of IF in the concentrated contact have been evaluated [6]. It was shown that the IF nanopaticles appear to form a pro- tective film allowing increased load capacity of the rubbed pairs under mixed lubrication. The improved tribological be- ∗ Corresponding author. Tel.: +972 3 5026616; fax: +972 3 5026619. E-mail address: rapoport@hait.ac.il (L. Rapoport). havior with IF-WS 2 was attributed to the decreasing fraction of straight asperity contact in the mixed lubrication regime. It was established that supplying pristine IF nanoparticles through the porous system of the powder materials endows a very high load bearing capacity for the powdered composites [7–9]. Recent experiments demonstrated the high efficacy of the IF nanoparticles under severe contact conditions. How- ever, the friction and wear properties of the IF nanoparticles under severe contact conditions are currently not well under- stood, especially in the critical point of transition to seizure. It is expected that the preservation of pristine IF nanopar- ticles in the clearance between the rubbed surfaces allows to improve remarkably the friction and wear properties of the contact pairs under severe contact conditions. The main objective of the present work is to evaluate the behavior of 0043-1648/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2005.01.009