EFFECTS OF LUBRICANTS ON FRICTION AND WEAR OF Si_3N_4 CERAMIC

The friction and wear properties of Si3N4/steel rubbing pairs were investigated by using a Pin-on-disk tribometer. Water, liquid paraffin and a commercial cutting fluid were uSed resistively as lubricants. The selected speed and load ranges for the tests were 0.8 to 3.2m / s and 58.8 to 235.2N. The effects of lubricants on the friction and wear of Si3N4/steel pairs showed great difference. The boundary lubricity of water in the t6sts was very POor, which could not well prevent the steel from transfering onto the Si3N4 surface in rubbing process. Liquid paraffin could form stronger lubicating film compared with water, but its boundary lubricity was not good enough for the lubrication of Si3N4/steel pair under relatively high load condition. The friction and wear increased gradually with the load when liquid paraffin was used for lubrication. The commerical cutting fluid GMY, in which some fat acid salt and surfactants were contained,showed excellent boundary lubricating characteristics. The POlar molecules of the compounds in the fluid could be adsorbed strongly on the rubbing surfaces by physical or chemical adsorption. In addition, some of the adsorbed molecules might react with the sliding surfaces to form tribolchemical reaction film. Both of the two films could decrease the friction and wear of the Si3N4/steel rubbing pairs under boundary lubrication conditions. It was also found that the boundary lubircity of the GMY fluid could be improved further when its concentration was increased.