Tribology and Interfaces

3-5026619(972)	:Fax	rapoport@hit.ac.il	:Email
3-5026636(972)	:Tel	3-5026616 (972)	:Tel

We deal with the interdisciplinary research and developments in the field of the tribology design. The mainstream of the laboratory activity lies currently in the study of friction and wear behavior of nano-materials, coatings and thin films. Deformation and fracture of surface layers under friction is analyzed. New and standard experimental-research methods are used in the study of deformation and fracture of surface layers in different contact conditions.

 

Current Research Themes

 

 

Laboratory Facilities o Different Friction and Wear Testers

 

Staff

Prof. Lev Rapoport - Head of Laboratory
Dr. Alexey Moshkovich – Friction and wear of solid lubricant
Dr. Vladislav Perfilyev – Development of solid lubricant films
Dr. Klara Yutudjan – Chemistry of friction surfaces
Dr. Igor Lapsker - Scanning Microscopy
Eng. Oleg Foigel – Design of mechanical parts

 

Services

 

 

Inorganic fullerene-like materials (IF) have been identified as being of potentially utmost importance for many industrial applications, as a consequence of their unique mechanical and electronic properties. In analogy to carbon fullerenes (C60, etc), fullerene-like materials are made of two-dimensional lamellar structure, like BN, CNx, MoS2, CdCl2, etc, with closed and curved morphologies, grown into three-dimensional networks or architectures and displaying a wide range of shapes. As a consequence of their atomic-scale structure involving strong covalent bonds and non-compact space filling, these materials have been identified as strong candidates for tribological applications such as solid lubricants. The analysis of the IF nanoparticles showed that most of all pristine nanoparticles were closed and hollow, having nearly spherical shape. The average size of the IF-WS2 particles was close to 120 nm.

 

Fig.1. IF- WS2 nanoparticles with close to roll shape show excellent tribological properties

 

 

The hydrostatic powder compression experiments were carried out using quasi-hydrostatic polyurethane bag tooling. It was found that these nanoparticles are capable of withstanding a severe hydrostatic pressure, caused by compression. Detailed structural studies revealed a deformation of the IF nanoparticles and breakage of their outer shells under compression. The exfoliation of only the external layers of the IF nanoparticles, preservation of their shape and their lattice parameter allude to the very high stiffness of fullerene-like nanoparticles. Mainly, only the outermost layers of the IF-WS2 medium are damaged, which affect on the tribological behavior of this material.

 

Fig. 2. HR-TEM image of delamination of external thin sheets of fullerene-like WS2 nanoparticles under compression.

 

 

Incorporation of solid lubricant into micro-reservoirs produced by Laser Surface Texturing (LST) and its effect on the tribological properties of surfaces under dry friction is studied. The density of the dimple reservoirs and the height of the bulges around them are investigated in terms of the longevity of solid lubricant films burnished on LST steel surfaces. Friction tests were performed using a ball-on-flat device. Optimum density (40-50%) of the dimples is revealed (Fig. 3). It is shown that the adhesion of solid lubricant in the space between the dimples is provided by mechanical engagement of particles in the rough surface and by smearing the solid lubricant around the dimples. Best results are obtained with surfaces that were lapped to half of the height of bulges. Long wear life of burnished film on LST steel surfaces is apparently provided by preservation of thin MoS2 film around the bulges and by supply of solid lubricant from the dimple

 

(b)

(a)

Fig. 3. MoS2 particles burnished into the dimples of laser textured surface (a). Single dimple burnished with MoS2 particles (b)

 

 

The nanoindentation and nanoscratching procedures were used for measuring mechanical characteristics of the thin coatings. Both procedures were performed with DI Dimension 3100 equipped with a diamond tip mounted to the end of the metal cantilever. This test was performed in order to evaluate the relative wearability of thin films in comparison to polymer substrates. Fig. 4 shows the scratches on the surface of SnO2 at different loads. Good adhesion is observed for all thin films studied. The cracks or delamination were not observed around the scratch tracks of films from the substrate. The wearability of SnO2 films is 50-80 times higher than for the polymer substrates.

 

Fig. 4. Nanoscratching of SnO2 thin film on the surface of polymer

 

 

 

Some micro-electro-mechanical systems have to provide very precise translation during motion after pauses. Increasing a time of the pauses (waiting time) usually raises the static friction overshoot, limiting thus the precision of these systems. The goal of this work was to study the effect of testing and waiting time; loading and unloading on static and kinetic friction for real contact microsystems.The testing rig is shown in Fig. 5.

Fig. 5. Set-up of glass samples in the friction device.

 

Fig. 6 Overshoot of the static friction force during first half of the cycle after stopping the test. Waiting time is 16 hours.

 

The effect of some types of silicone fluids on static friction was studied. The stick-slip phenomena with silicone fluids between glass surfaces was evaluated. The silicone fluids with viscosity of 100 cSt; 450 cSt, and 5000 cSt were studied. The effect of waiting time on the static friction was analyzed. The value of the static force overshoot increased with a waiting time. The change of the friction force in the first half of the cycle after long waiting time (16 hours) is shown in Fig. 6. The minimal value of the critical shear force observed for silicone fluid with viscosity of 450 cSt can be attributed to small number of the molecular "bonds" and little interdigitation of the chains in comparison to PDMS and DPSDMS liquids.

 

 

Our Investigations in the field of the Tribological Properties of inorganic fullerene like nanomaterials has been approved for support by the Binational Science Foundation (BSF) in 1998 year and by the Israeli Ministry of Science (1999). The investigation in the field of improvement of tribological properties of laser textured surfaces by filling the dimples with solid lubricant nanoparticles has been supported by the Israeli Ministry of Science (2005).

 

Some of last important results (2002-2008) are published in :

L. Rapoport, V. Leshchinsky, M. Lvovsky, I. Lapsker, Yu. Volovik, R. Tenne, Load bearing
capacity of bronze, iron and iron-nickel powder composites containing fullerene-like WS2
nanoparticles, "Tribology Int'l”, 35 (2002) 47-53.

L. Rapoport, V. Leshchinsky, M. Lvovsky, O. Nepomnyashchy, Yu. Volovik, R. Tenne, Friction
and wear of powdered composites impregnated with WS2 inorganic fullerene-like nanoparticles,
Wear, 252 (2002) 518-527.

V. Leshchinsky, E. Aloyshina, M. Lvovsky, Y. Volovik, I. Lapsker, R. Tenne, L. Rapoport,
Inorganic nanoparticle impregnation of self lubricated materials, Int'l. J. of Powder Metallurgy,
38(5) (2002) 50-57.

L. Cizaire, B. Vacher, T. Le Mogne, J.M. Martin, L. Rapoport, A. Margolin, R. Tenne, Mechanisms of ultra-low friction by hollow inorganic fullerene-like MoS2 nanoparticles, Surface and Coatings Technology, 160 (2002) 282-287.

L. Rapoport, V. Leshchinsky, Yu. Volovik, M. Lvovsky, O. Nepomnyashchy, Y. Feldman, R. Popovitz-Biro, R. Tenne, Modification of contact surfaces by fullerene-like solid lubricant nanoparticles, Surface and Coatings Technology, 163-164 (2003) 405-412.

L. Rapoport, N. Fleischer, R. Tenne, Fullerene-like WS2 nanoparticles: Superior lubricants for harsh conditions, Advanced Materials, 15(7-8) (2003) 1-5.

L. Rapoport, V. Leshchinsky, I. Lapsker, Yu. Volovik, O. Nepomnyashchy, M. Lvovsky,
R. Popovitz-Biro, Y. Feldman, R. Tenne, Tribological properties of WS2 nanoparticles under mixed lubrication, Wear, 255 (2003) 785-793.

L. Rapoport, V. Leshchinsky, M. Lvovsky, I. Lapsker, Yu. Volovik, Y. Feldman, R. Popovitz-Biro, R. Tenne , Superior tribological properties of powder materials with solid lubricant nanoparticles,
Wear, 255 (2003) 794-800.

V. Leshchinsky, R. Popovitz-Biro, K. Gartsman, R. Rosengveig, Yu. Rosenberg, R. Tenne, L. Rapoport, Behavior of solid lubricant nanoparticles under compression, J. Materials Science, 39,
( 2004) 4119-4129.

L. Rapoport, O. Nepomnyashchy, A. Verdyan, R. Popovitz-Biro, Volovik, B. Ittah, R. Tenne,
Polymer nanocomposites with fullerene-like solid lubricant, Advanced Engineering Materials, 6(1/2), (2004) 44-48.

L. Rapoport, O. Nepomnyashchy, I. Lapsker, A. Verdyan, A. Moshkovich, Y. Feldman, R. Tenne,
Behaviour of fullerene-like WS2 nanoparticles under severe contact conditions, Wear, 259
(2005) 703-707.

L. Rapoport, N. Fleischer, R. Tenne, Applications of WS2 (MoS2) inorganic nanotubes and
fullerene-like nanoparticles for solid lubrication and for structural nanocomposites, J. of Materials Chemistry, 15 (2005) 1782-1788.

L. Rapoport, O. Nepomnyashchy, I. Lapsker, A. Verdyan, Y. Soifer, R. Popovitz-Biro, R. Tenne,
Friction and wear of fullerene-like WS2 under severe contact conditions: Friction of ceramic materials, Tribology Letters, 19(2) (2005) 143-149.

A. Margolin, R. Popovitz-Biro, A. Albu-Yaron, L. Rapoport, R. Tenne, Inorganic fullerene-like nanoparticles of TiS2, Chemical Physics Letters, 411 (2005) 162-166.

V.N. Zhitomirsky, T. David, R.L. Boxman, S. Goldsmith, A. Verdyan, Ya. M. Soifer, L. Rapoport,
Properties of SnO2 coatings fabricated on polymer substrates using filtered vacuum arc deposition,
Thin Solid Films, 492 (2005) 187-194.

A. Katz, M. Redlich, L. Rapoport, H.D. Wagner, R. Tenne, Self-lubricating coatings containing fullerene-like WS2 nanoparticles for orthodontic wires and other possible medical applications, Tribology Letters, 21(2), (2006) 135-139.

V. Perfiliev, A. Moshkovith, A. Verdyan, R. Tenne, L. Rapoport, A new way to feed nanoparticles to friction interfaces, Tribology Letters, 21(2) (2006) 89-93.

A. Moshkovith, V. Perfiliev, A. Verdyan, I. Lapsker, R. Popovitz-Bro, R. Tenne, L. Rapoport,
Sedimentation of IF-WS2 aggregates and a reproducibility of the tribological data, Tribology
International, 40 (2006) 117-124.

A Moshkovith, V. Perfiliev, I. Lapsker, N. Fleisher, R. Tenne, L. Rapoport, Friction of fullerene-
like WS2 nanoparticles: effect of agglomeration, Tribology Letters, 24(3) (2006) 225-228.

S. Arad, L. Rapoport, A. Moshkovich, D. van Moppes, M. Karpasas, R. Golan, Y. Golan, A
superior biolubricant extracted from a species of red microalga, Langmuir, 22 (2006) 7313-7317.

H. Friedman, O. Eidelman, Y. Feldman, A. Moshkovich, V. Perfiliev, L. Rapoport, H. Cohen, A. Yoffe, R. Tenne, Fabrication of self-lubricating cobalt coatings on metal surfaces, Nanotechnology, 18, 2007 (8 pages) [appearing on Nanotechnology website, not yet in the printed issue].

L. Rapoport , A. Moshkovich , V. Perfilyev, R. Tenne, On the Efficacy of IF–WS2 Nanoparticles as Solid Lubricant: The Effect of the Loading Scheme, Tribology Letters, 28 (2007) 81-87.

A. Moshkovich, V. Perfilyev, K. Yutujyan, L. Rapoport, Friction and wear of solid lubricant films deposited by different types of burnishing, Wear, 263 (2007) 1324-1327.

A. Moshkovith , V. Perfiliev, D. Gindin, N. Parkansky, R. Boxman, L. Rapoport, Surface texturing using pulsed air arc treatment, Wear, 263 (2007) 1467-1469.

L. Rapoport, A. Moshkovich, V. Perfilyev, I. Lapsker, G. Halperin , Y. Itovich, I. Etsion, Friction and wear of MoS2 films on laser textured steel surfaces, Surf. Coat. Technol, 202 (2008) 3332-3340.

B. Sp?th, F. Kopnov, H. Cohen, A. Zak, A. Moshkovich, L. Rapoport, W. J?germann, and R. Tenne, X-ray photoelectron spectroscopy and tribology studies of annealed fullerene-like WS2 nanoparticles, phys. stat. sol. (b) (2008) 1– 6.