Mark Lvovsky

Superior tribological properties of powder materials with solid lubricant nanoparticles

Abstract Friction and wear of powder materials impregnated with commercially available layered (platelets) WS 2 (2H) and inorganic fullerene-like WS 2 nanoparticles (IF) were studied. Bronze–graphite, iron–graphite and iron–nickel–graphite samples were used in this experiment. The linear wear of powder materials (in situ) was measured. It was shown that the IF nanoparticles impregnated into the pores improve the tribological properties of powder materials in comparison to a reference sample or the sample impregnated with 2H solid lubricant particles. The mechanisms of friction and wear of the IF nanoparticles have been considered. The tribological role of the wear particles and nanoparticles of solid lubricants has been analyzed in the framework of a third body lubrication model. The state of the IF nanoparticles before and after the wear test was studied. It was found that the shape of the IF nanoparticles is preserved during the friction tests under high loads. Thin wear debris surrounded by spherical IF nanoparticles appear to be formed and provide easily sheared lubrication film (low friction coefficient) during friction experiments of powder materials containing IF nanoparticles.

Mechanism of friction of fullerenes

In the past few years, inorganic fullerene‐like (IF) supramolecules of metal dichalcogenide WS2 and MoS2 with structures closely related to (nested) carbon fullerenes and nanotubes have been synthesized. Recent experiments showed that IF added to oil and impregnated into the porous matrixes possess lubricating properties superior to those of layered WS2 and MoS2 (2H platelets). The main goal of this work was to analyze the mechanism of friction of fullerene‐like nanoparticles. Friction and wear behavior of IF in different contact conditions is studied. Third body model is considered. Sliding/rolling of the IF nanoparticles in the boundary of the first bodies and in between the wear particles (third body) is supposed to facilitate the shear of the lubrication film. Broken and oxidized 2H‐WS2 small pieces adhered to wear debris do not provide high tribological properties especially under high loads.

Friction and wear of powdered composites impregnated with WS2 inorganic fullerene-like nanoparticles

The impregnation of inorganic fullerene-like nanoparticles of WS2 (IF) allows to improve effectively the tribological properties of powdered materials in comparison to the impregnation of oil or commercially available layered WS2 (2H) particles. The main goal of this work was to determine the dominant lubrication regimes under friction of the bronze, iron, and iron–nickel porous matrixes impregnated with 2H and IF solid lubricants. The tribological tests were performed at laboratory atmosphere (humidity ∼50%) using a ring-on-block tester at the sliding speed of V = 1 m/s, and the loads of 150–1000 N. The wear of the metal bodies was measured by an eddy current probe system and by weighting of the samples before and after the test. In order to evaluate the radial clearance, the profiles of wear blocks were analyzed by profile projector. Than these data were used in the calculation of the Sommerfeld reciprocal values. Friction and wear results were presented as the Stribeck curves. The critical Sommerfeld reciprocals were evaluated from these curves. The Stribeck curves were compared with the Morgan’s curves for different ranges of non-dimensional permeability, Ψ . These results are used then in calculation of the permeability, Φ. Three lubrication regimes as: quasi-hydrodynamic, boundary or mixed, and dry friction were revealed under friction of porous samples in the load-range studied. It was found that the impregnation of IF nanoparticles provides the regime of quasi-hydrodynamic lubrication in the widest range of loads in comparison to the reference sample and the sample impregnated with 2H–WS2. Fe–Ni samples exhibited the highest wear resistance and provided the widest range of quasi-hydrodynamic lubrication in comparison to bronze and iron powdered composites. The effect of IF on the regimes of lubrication is explained on the base of the third-body model. It is expected that the sliding/rolling of the IF nanoparticles in the boundary of the first bodies and in between the wear particles (third-body) facilitate the shear of the lubrication film and thus provide the quasi-hydrodynamic regime of friction. It is supposed that the roll shape of IF nanoparticles allows to release the IF from the pores to contact surfaces.