Research On The Forming And Lubricating Mechanism Of In-Situ Reaction Lubricating Film Containing B-O Compound

In this paper,the tribological properties of Si₃N₄-hBN ceramic composites sliding against austenitic stainless steel?ASS?were studied in dry and compound lubrication condition?pure water,seawater and epoxidized vegetable oils?.The formation process,conditions and lubricating substances of the friction chemical reaction film on the worn surface are mainly studied through the observation method of the grinding section.The purpose is to reveal the formation and lubrication mechanism of the in-situ lubrication film.The friction and wear tests were carried out on MMW-1 tester.The morphologies and phase compositions of the worn surfaces and wear debris were observed by scanning electron microscope,X-ray diffractometer and X-ray photoelectron spectrometer.Through the research,the conclusions are as follows:In dry condition,the friction coefficient of SN10/ASS pair at about 800m reached the lowest value?0.05?under a normal load 10N,speed 500r/min,and kept the low friction state all the time,which contribute to a black surface film containing SiO₂,Fe₂O₃,H₃BO₃ and metallic element was formed on the worn surface,the film lubricated and protected the worn surface.Through segmental test and investigation,we find that when the grinding process reaches about 200m,the worn surface begins to generate a lot of peeling pits.When the grinding process reaches about 500m,a lot of debris began to be filled in the peeling pits.When the grinding process reaches 800m,the friction products of the wear debris in peeling pits reacted with the water molecules in the air were produced and enriched in the peeling pits,at the same time the friction products in the peeling pits were dragged to form a film under the action of friction.When the friction test continues,the black oxide film on the worn surface of SN10/ASS pair was damaged when the grinding distance reaches 2000m or even 3000m,with the increase of the friction distance,the friction coefficient increases slowly eventually stabilized at about 0.5.The tribological properties of the Si₃N₄-hBN pin specimens of other hBN content sliding against ASS steel are worse than the SN10/ASS pair.In pure water,the tribological properties of SN10/ASS pair are better than SN0/ASS pair.The friction coefficient of SN10/ASS pair reaches 0.1 at finally stable state,and the worn surface was also smooth.This was mainly contributed to the debris flow away easily,thus avoiding abrasion in the water environment.The friction and chemical products of the wear debris in the peeling pits reacted with water containing SiO₂,B₂O₃ and Fe₂O₃ were dragged into a film under the action of friction and the film protect and lubricate the worn surface.In the same experimental conditions,the tribological properties of SN10/ASS pair were in seawater worse than in pure water condition.Although the tribochemical reaction film containing Si O₂ and Fe₂O₃ was formed on the worn surface,Ca²⁺and Mg²⁺ions were not conducive to the enrichment of lubricated B-containing compounds on the friction surfaces,and the chemical polishing in seawater condition was not obvious.In modified vegetable oil condition,the SN10/ASS pair obtained the best tribological properties in the lubricating oil of epoxidized rapeseed oil,and its stable friction coefficient reached 0.09,and the modified vegetable oil had better lubrication effect than mineral oil.For the modified vegetable oil,the addition of solid lubricant does not play the role of anti-friction,contrary increase the abrasive wear.Through the calculation of Gibbs free energy of tribological reaction,it is found that the Gibbs free energy of friction chemistry reaction is negative at room temperature,it is proved that tribological reaction can occur spontaneously at room temperature.By improving the Arrhenius formula,the rate V₁ of the tribological reaction is calculated.It is found that it has little relation with the temperature,and has a great relationship with the activation energy E_a.According to the Hertz contact theory,the formula of the friction coefficition?is calculated when the friction pair in the state of boundary lubrication.