Research On The Evolution Behavior Of Third-body Layer On The Surface Of SiCp/A356 Composites Under Service Environment

SiC particles reinforced aluminum matrix has been used as an advanced urban rail brake disc material,which friction and wear properties impact on the security,reliability and comfort of trains.The third body formed on the friction surface determined the contact status of friction pairs,such influenced the tribological behavior.Therefore,it's very important to take research on the evolution of third body under different conditions.In this paper,tests based on cons speed experiment methods under conditions of load<300 N,velocity ?1000 rpm,time ?10 min in dry,wet environment or different temperature sections between 30?300 ? have been carried out.The main contents and conclusions of this paper are as follows:(1)The evolution of third body under dry and wet conditions has been demonstrated.The third body has formed on the friction surface of aluminum matrix during sliding tests with semimetallic pad material.The surface and subsurface characteristic of the layer were studied by optical morphology microscope,scanning electron microscope and Energy-dispersive X-ray spectroscopy,and the evolution process has been divided into three stages to summarize the mechanism for formation and destruction of the layers.(2)The different evolution mechanism of third body under dry and wet conditions has been expounded.The formation of the third body is inhibited under the wet condition,and there are large number of micro defects in the layer,which made the damage occurred easily,resulting in the fluctuation of friction coefficient and increase in wear rate of SiCp/A356.(3)The difference of formation and evolution of the third body under effect of temperatures has been studied to give the reason of the decrease of friction properties and wear resistance under high temperature.The mechanism of prefabricated third body to improve tribological behavior at high temperature has been proposed.The paper has a clear engineering background.The research result has not only enriched the tribological theory of SiCp/A356 composites,but also has provided scientific support for the application of SiCp/A356 composites in the brake disc of urban railway trains.What the paper mentioned will be of great value to the application of SiCp/A356 in engineering.