Understanding the lubrication mechanism between the polyhydroxyl group lubricants and metal surfaces

Abstract

This paper presents the comparative studies to clarify the tribochemical reactions and disclose the tribochemical mechanisms of the polyhydroxyl group lubricants with different molecular structures and the lubrication performances of the friction pair of Nitinol alloy pin/high speed steel disc using pin-on-disc tribometer. The tribotest results show that all polyhydroxyl group lubricants can improve the lubrication performances of the friction pair and only castor oil exhibits super low friction of 0.005. It is shown that there is first the dissociation of castor oil in the presence of ester groups and then castor oil and the hydrolysis products of castor oil are easily oxidized by oxygen due to the double bonds and hydroxyl groups under the friction heating and high pressure. The sole results of the dissociations of castor oil and tribological oxidations are the provisions of the chemical reaction pathways to form the OH-terminated surfaces. Super low friction of the friction pair under castor oil lubrication can be attributed to occurring between the triboinduced degradations and oxidations, tribochemical reactions and triboformed OH-terminated surfaces resulting in the strong repulsive forces. These experimental results and analyses will support strongly and elucidate the super low friction mechanism from both scientific and application viewpoints.