Effect Of Si Content In Si-DLC Film On The Growth Of ZDDP Tribofilm

Silicon doped diamond-like carbon(Si-DLC)film is considered as an unique candidate material for engine parts in recent years due to its excellent wear resistance,low friction,thermal stability and chemical inertness.It is often used in poor working conditions such as piston rings.However,the different content of Si greatly affects the physical and chemical properties of Si-DLC films,such as hardness,internal stress,thermal expansion coefficient,etc,which makes the films have different properties.Zinc dialkyl dithiophosphate(ZDDP),because of its excellent anti-wear performance,it has been used as anti-wear additive in automobile engine piston rings for many years.Based on the macroscopic study,ZDDP molecules would decompose at the friction interface due to pressure,heat,or other effects,forming glassy phosphate,and gradually develop from plaque to continuous friction film to protect the surface,so as to reduce wear,adhesion,and direct contact between metal and other materials.It is very important to know whether the traditional anti-wear additive can form lasting film with Si-DLC and work effectively.The existing macro characterization technology can?t enter the sliding interface,which hinders the study of the tribological process.In this experiment,Si-DLC samples with different silicon content are used to design different sliding cycles,temperature and contact stress.The in-situ friction experiment is carried out by using atomic force microscope(AFM),and the growth and properties of the tribofilm are analyzed in situ to explore the influence of Si element content on the lubrication performance of Si-DLC film in ZDDP.The results are as follows:1)The increase of contact stress could promote the decomposition of ZDDP,which was conducive to the formation of tribofilm,and the forming rate of tribofilm increased with the increase of contact stress.The tribofilm first grew linearly,and then grew exponentially with the increase of sliding cycles.2)The decomposition rate of ZDDP and the growth rate of reaction membrane increased with the increase of temperature.On the surface of a-C:H:Si-35.6 at.%,the temperature increased from 80 ? to 100 ?,the height of ZDDP tribofilm increased3)The results showed that the growth of tribofilm on a-C:H:Si-35.6 at% was better than that of a-C:H:Si-8.9 at.% Moreover,contact stress and surface effect had synergistic effect on the growth of ZDDP tribofilm.Therefore,the growth of tribofilm on the surface of a-C:H:Si-35.6 at.% sample was obviously better than that on the surface of a-C:H:Si-8.9 at.%.