ULTRA LOW-FRICTION CHARACTERISTICS OF NANOSTRUCTURED SURFACES ON SILICON NITRIDE IN AQUEOUS MEDIUM

Even though studies have shown unequivocally that the coefficient of friction of self-mated silicon nitride can be quite low in water, the basic phenomena responsible for such a low friction is still controversial. in this investigation the effects of load, speed, and surface roughness on the duration of the run-in period for self-mated silicon nitride in water was studied. although the results are consistent with proposed mechanisms involving mixed hydrodynamic lubrication by water and boundary lubrication by colloidal silica, an alternate mechanism is suggested. the friction and wear tests were conducted using a pin-on-disk tribometer. the surface roughness of the disks was measured with an atomic force microscope (afm) scanning several areas 50x50 μm in dimensions. for a test on a lapped surface at 5 n and 120 mm/s, the coefficient of friction is seen to decrease from an average of 0.45–0.01 after 600 min. it is proposed that the low friction could be also related to fundamental interactions between two hard and elastically deforming surfaces covered with hydrogen-terminated oxide films.