Effects Of Temperature On Tribological Properties Of Hard Coatings Under MoDTC Lubrication

The combinations of hard coatings and favorable lubrication conditions were effective ways to improve the tribological properties of mechanical parts.However,the tribological mechanism researches of the composite effect between lubricating oil including additives and hard coatings were not deep enough at present.In this paper,the effects of temperature on the friction and wear properties of CrN,TiN and W-doped diamond-like carbon?W-DLC?coatings were examined under synthetic oil polyalphaolefin?PAO?without and with molybdenum dialkyldithiocarbamate?MoDTC?lubrications,and the friction reduction and antiwear mechanisms were also analyzed.This research had important theoretical significance and application value.The results are as follows:?1?Under PAO lubrication,the coefficients of friction?COFs?of CrN/GCr15 friction pairs,the wear rates of Cr N coatings and worn scar diameters of counter balls gradually increased with the increase of temperature.The addition of MoDTC reduced the COFs,and decreased the wear rates of CrN coatings and worn scar diameters of counter balls to a certain extent.Under MoDTC lubrication,the COFs and wear rates of CrN coatings showed a variation tendency of decreasing first and then increasing with the increase of temperature,while the worn scar diameters of counter balls given the opposite change tend.The tribological performance of CrN coating was relatively better at 75 ?,which is attributed to the larger MoS₂/MoO3 ratio from the tribofilm formed on the worn surface of friction pair.The microstructure analysis of the worn surfaces shown that the wear mechanisms of CrN coatings included abrasive wear,fatigue wear,oxidation wear and slight adhesion wear.?2?Under PAO lubrication,the COFs of TiN/GCr15 friction pairs and the wear rates of TiN coatings gradually increased with the increase of temperature,while worn scar diameters of counter balls showed a variation tendency of decreasing first and then increasing slowly after 50 ?.The addition of MoDTC reduced the COFs,and improved the wear resistance of TiN coatings and their counter balls.The COFs decreased first and then increased,the wear rates of TiN coatings increased gradually,and the worn scar diameters of counter balls showed a whole variation tendency of decreasing with the increase of temperature.The tribological performance of TiN coating shown relatively better at 50 ?,which is attributed to the larger MoS₂/MoO3 ratio and the more contents of TiO₂ and FeSx with the friction reduction effect from the tribofilms.The wear mechanisms of TiN coatings were abrasive wear,oxidation wear and slight adhesion wear at a higher temperature.?3?Under PAO lubrication,the temperature had little influence on the COFs of W-DLC/GCr15 friction pairs.The wear rates of W-DLC coatings and the worn scar diameters of counter balls decreased with the increase of temperature,which is obvious at 125 ?.The addition of MoDTC also reduced the COFs and improved the wear resistance of W-DLC coatings,while increased the wear of their counter balls.The COFs,the wear rates of W-DLC coatings and the worn scar diameters of counter balls all decreased first and then increased with the increase of temperature,and also decreased to a certain extent at 125 ?.The tribological performance of W-DLC coating was relatively excellent at 75 ?,which is also attributed to the more contents of MoS₂ and FeSx.The difference was that the tribological behaviors of W-DLC coatings were relevant with the degree of graphitization of the worn surfaces as well as at different temperatures.The wear mechanisms were abrasive wear,oxidation wear and slight adhesion wear.