A comparative study of the tribological performance of ferrofluids and magnetorheological fluids within steel-steel point contacts

The lubricating properties of two different magnetic colloids were evaluated both in the absence and presence of external magnetic fields under sliding friction using the ball-on-three-plates geometry and stainless steel-steel point contacts. Specifically, the magnetic colloids studied were commercially-available ferrofluids (i.e., low concentration dispersions of nanosized magnetic particles) and magnetorheological fluids (i.e., high concentration dispersions of microsized magnetic particles). To evaluate the wear damage, the wear scar on the steel plates was examined by optical microscopy and scanning electron microscopy. Experimental results demonstrate a clearly lower friction coefficient and wear damage under lubrication with the ferrofluid, indicating that the effect of particle concentration in the magnetic dispersions dominate over that of particle size.