TRIBOCHEMICAL MECHANISMS OF SI3N4 WITH ADDITIVES

The effects of several extreme pressure additives on the wear behaviou r of silicon nitride (Si3N4) were investigate using a reciprocating we ar tester; the tribochemical reaction mechanisms of Si3N4 with these a dditives were studied by means of scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The wear tests show that the additives have different antiwear functions compared with n-t etradecane in the order tridodecyl borate almost-equal-to tributyl pho sphate (TBP) < chlorinated paraffin < sulphurized olefin almost-equal- to zinc dialkyldithiophosphate (ZDDP). The analytical results of profi les and compositions of worn surfaces indicate that, under various lub ricated conditions, Si3N4 oxidizes and forms crystalline SiO2. ZDDP, s ulphurized olefin and chlorinated paraffin are effective in antiwear a ction, because of the formation of tribochemical reaction products obt ained from the reaction with SiO2, while TBP and tridodecyl borate hav e little antiwear function because of their physical adsorption on the rubbing surfaces.