Studying The Friction And Wear Behaviors Of Amorphous Carbon Films In Hydrochloric Acid

Tribo-corrosion could be occurred when the mechanical components are in service under corrosion environment.Tribo-corrosion not only causes surface damage and material consumption,but also leads to serious economic losses and unpredictable disasters.Diamond-like carbon film(DLC)is widely used as surface protection coating due to its high hardness,excellent friction-reducing ability,high wear-resistance,and outstanding chemical inertness.There are many researches on the tribological behavior of DLC film in corrosive solution,which provides feasibility for the application of DLC film in harsh environment.However,the tribological performances of DLC films in hydrochloric acid(HCl)receive much less attention,especially the influence of test conditions such as load,counter materials and solution concentration on the tribological properties of DLC film in HCl.Moreover,researchers mainly focused on the description of the tribological behavior process of DLC film in HCl,which lack the in-depth explanation of its wear mechanism.In response to the above questions,we systematically analyzed the influence of load(contact stress),counter materials and solution concentration on the tribological performances of DLC film in HCl,and explained the essential wear mechanism of DLC film according to the results,which providing theoretical guidance for the matching materials of Cr-DLC film in HCl.The main conclusions are as follows:(1)Cr-doped DLC films(Cr-DLC)were fabricated by an unbalanced magnetron sputtering(UBMS),and systematically studied the effect of applied load(contact stress)on the tribological behaviors of Cr-DLC film in 0.3M HCl.Results shows that friction coefficient(COF)of Cr-DLC films follow with the Hertzian elastic contact in HCl solution,that is,the COF gradually declines with increasing contact load except 2 N.The Cr-DLC film shows the best wear resistance at 5 N,which the wear rate is about 1.79×10^-7 mm³/Nm.The main wear mechanism of Cr-DLC film at low contact loads(2 N and 5 N)is attributed to the formation of graphite-like transfer film and tribo-chemical products on friction interfaces;And the wear mechanism at high contact loads(7 N and 10 N)is mainly affected by the synergistic effect of the high Hertzian contact stress and the corrosion function of chloride ion.Cr-DLC exhibits lower wear rate and friction coefficient in HCl at high contact stress,which indicates that the Cr-DLC film can obtain robust lubricity at high loading.(2)To further improve the tribological performances of Cr-DLC film,we systematically evaluated the tribological performances of Cr-DLC films against different mating materials(GCr15 steel ball,Si₃N₄ ceramic ball,ta-C,H62 brass ball)in 0.3M HCl.Result shows that the ta-C/Cr-DLC tribo-pair presents the most excellent tribological properties.When Cr-DLC film rubbed against the different mating materials,the rank of COF is?H62/Cr_-DLC>?GCr15/Cr_-DLC>?Si3N4/Cr_-DLC>?ta_-C/Cr_-DLC,which is mainly governed by the contact pressure,the sp³?sp² phase transition and the tribo-chemical reaction;The wear rate of Cr-DLC film from high to low is WSi3N4/Cr_-DLC>WH62/Cr_-DLC>Wta_-C/Cr_-DLC.The wear behavior is mainly depended on the generation of tribo-chemical products during the friction process in0.3M HCl.(3)The above researches indicate that the ta-C/Cr-DLC tribo-pair shows better tribological performance than other tribo-pairs in 0.3M HCl.However,the concentration of HCl will change in actual application conditions.Does ta-C/Cr-DLC tribo-pair still maintain low friction coefficient and high wear-resistance in different concentrations of HCl?This is great significance for the development of practical applications of carbon-based friction coatings.Therefore,we systematically studied the tribological behaviors of ta-C/Cr-DLC tribo-pair in different molar concentrations of HCl.It is found that the COF and wear rate of ta-C/Cr-DLC tribo-pair does not change significantly in the different molar concentrations of HCl,which indicates that the ta-C/Cr-DLC tribo-pair have great environmental adaptability.In different concentrations of HCl,the excellent tribological performance of ta-C/Cr-DLC is mainly derived from the passivation effect of-OH or-H groups on the surface dangling bonds of Cr-DLC and ta-C film,the formation of low-adhesion water layer and the graphitization transfer layer on the friction interfaces.