Load bearing capacity of bronze, iron and iron-nickel powder composites containing fullerene-likeWS2 nanoparticles

In the past few years, inorganic fullerene-like (e.g. IF) supramolecules of metal dichalcogenide MX2 (M=Mo,W, etc.; X=S, Se), materials with structures closely related to (nested) carbon fullerenes and nanotubes have been synthesized. Recent experiments showed that IF possess lubricating properties superior to those of commercially available layered solid lubricant (2H-WS2 polytype) in a wide range of operating conditions. It was shown before that the impregnation of a small amount of such nanoparticles into porous bronze matrix largely improve the tribological properties of bronze-steel contact pairs. In the present work, the effect of the PV (pressure-velocity) parameter on the transition to seizure for powdered bronze-graphite, iron-graphite and iron-nickel-graphite composites impregnated 2H and IF lubricant has been studied. The tribological tests were performed using a ring-block tester at loads of 150-1200 N and sliding speeds from 0.5 to 1.7 m/s. It was found that impregnation of IF into the pores improves the tribological properties of the powdered composites in comparison to 2H-WS2 solid lubricant. Furthermore, it was established that the impregnation of oil together with the IF nanoparticles allows to provide very high load bearing capacity of the powdered materials. It is suggested that the transition to seizure occurs when the wear debrises accumulate in the pores on the surface. This process practically blocks the surface pores and limits the supply of the solid lubricant particles to the contact surface. The main advantage of the IF nanoparticles is attributed to: (a) slow release and supply of nanoparticles from the open pores to the surface; (b) sliding/rolling of the IF between the rubbing surfaces; and (c) prevention of the accumulation of the agglomerated wear particles in the pores. The model of third body was used in order to explain the effect of the wear particles, oil and solid lubricant particles on the friction and wear behavior of powdered composites. (C) 2002 Elsevier Science Ltd. All rights reserved.