石墨烯对聚脲脂高温流变和摩擦学性能的影响OA北大核心CSTPCD

With the development of machinery industry,the bearing is required to work under elevated operating temperature and it is of great significance to study the tribological and rheological properties of the bearing grease at various working temperature in order to ensure the safety and reliability of the bearing system.Additives are critical to improve performance of lubricating grease.Herein,the graphene prepared by mechanical exfoliation method was used as the lubricating additive of polyurea lubricating grease,and its effect on the tribological and rheological properties of the polyurea lubricating grease at different working temperature was investigated by a four-ball tribometer and rotational rheometer.The morphology and structure of the wear spot were observed through a three-dimension optical profilometer,scanning electron microscopy and Raman spectroscopy.Findings indicated that,graphene sheets were filled and covered in the three-dimensional network structure of the polyurea thickener,which was beneficial to maintain the structural stability of the thickener.After ageing for 48 h at 150℃,the cone penetration(1/4)of the grease increased by 7.3 mm,while that of the grease with 1.0%graphene sheets additives retained almost constant(1.2 mm).The results of rheological tests showed that the structural strength of blank grease decreased at high temperature,while graphene sheets could effectively improve the shear stability resistance.The three-dimensional network structure formed by thickener fibers was easily deformed or even flowed and tended to be oriented under shear stress,while the directional arrangement of thickener fibers of the grease with graphene additives was blocked,so that the strain value of the flow point increased.As compared with blank polyurea lubricating grease,the same grease containing 1.0%(mass fraction)of graphene could reduce the coefficient of friction and wear spot diameter of bearing steel sliding pair working at 75℃and 150℃by 49%and 20%as well as 10%and 20%,respectively.There were many pits and furrows on the worn surface of steel balls lubricated by blank grease at the temperature of 75℃,when the temperature rose to 150℃,the worn surface became serious peeled off and showed typical adhesive wear characteristics.However,at the temperature of 75℃and 150℃,the worn surface of steel ball lubricated with 1.0wt.%graphene-polyurea grease was smooth,which was attributed to the large surface energy of graphene eventually contributing to adsorb on the surface of metal friction pair and form a deposition film composed with carbon and oxygen elements.With the increase of working temperature,the proportion of the ordered structural carbon in the deposited film of graphene-containing polyurea lubricating grease slightly decreases,but the proportion of ordered structural carbon in its deposited film is much higher than that of the blank grease.The formation of the ordered structural carbon plays a key role in improving the friction-reducing and antiwear abilities of the base grease,while the graphene as the lubricating additive also contributes to effectively improving the hardening behavior and colloidal stability of the polyurea grease as well as the structural stability of the thickeners.