Microstructure And Tribological Properties Of Co-doped Diamond-like Carbon Films

Titanium alloy,with the characteristics of low relative density,high thermal strength and good biocompatibility,has extremely important application value in aviation,aerospace,navigation,biomedicine and other fields.However,low hardness and poor anti-friction as well as wear resistance have always been the bottleneck of its popularization and application.Diamond like carbon(DLC)film is a new kind of film material similar to diamond,which has low friction coefficient,high hardness and high chemical stability.With the advantages of simple equipment,mild reaction conditions and easy to realize industrial production,liquid-phase electrochemical deposition technology has broad development prospects.The purpose of this project is to prepare diamond-like carbon(DLC)films on titanium alloy by liquid-phase electrochemical deposition.The appropriate co-doping elements were discussed,the deposition parameters were optimized,and then the microstructure and friction and wear behavior of the films were studied,so as to improve the wear resistance and friction reduction performance of titanium alloy and expand its application field.The main research contents and conclusions are as follows:(1)Ni/N-DLC films were prepared on TC4 titanium alloy by liquid-phase electrodeposition under mild environment(45 V,60℃)with anhydrous ethanol as carbon source and carboamide and nickel chloride as dopants.The effect of carboamide addition on the microstructure and properties of Ni/N-DLC films was evaluated,and the mechanism of electrochemical deposition for Ni/N-DLC films was explored.Results revealed that when the carboamide addition was 0.04 g/350mL,the particles of the matrix clusters were uniform and fine,and the average size was about 150-300 nm.Meanwhile,the relative content of sp3 hybrid carbon(70.59%)was significantly higher than that of sp2 hybrid carbon(6.28%).The micro Vickers hardness of Ni/N-DLC film was the highest,and the friction coefficient and wear loss were the lowest,which were 461.50 HV,0.179 and 3.33×10-5 kg/m,respectively.The CN groups formed at the cluster interface can inhibit the interaction between the hanging bonds on the film surface and the wear parts and the surrounding environment,thus effectively reduced the friction drag between the friction pairs.(2)The effect of rGO concentration on the microstructure and properties of Ni/N/rGO-DLC films was studied,and the influence of rGO concentration on the dispersion of the electrolytic system and the formation mechanism of the protrusions and gullies of Ni/N/rGO-DLC films were discussed.Results showed that the deposition of rGO particles tended to be vertical to the substrate,but the distribution was random.With the increase of rGO concentration to 0.07 g/L,the amorphous carbon matrix was obviously refined,and the average size was about 50～80 nm.Compared with Ni/N-DLC(0.04 g/350mL)films,micro Vickers hardness of Ni/N/rGO-DLC(0.07 g/L)films was increased by 28.25%.At the optimum concentration of rGO,the friction coefficient and wear loss of Ni/N/rGO-DLC films reached the minimum values of 0.072 and 1.20×10-4 kg/m,respectively.The exfoliated rGO particles can act as a solid lubricant between the friction pairs and repair the damaged graphitized transfer film in time.(3)The effect of MWCNTs concentration on the microstructure and properties of Ni/N/MWCNTs-DLC films was investigated,and the friction and wear mechanism for Ni/N/MWCNTs-DLC films was explored.Results demonstrated that the PDDA-MWCNTs composites tended to deposit in a way parallel to the substrate,and the MWCNTs between the clusters have a "bridging" effect,which can effectively reduce the undulation of the surface protrusions.When the MWCNTs concentration was 0.06 g/L,the films with smooth and compact morphology were achieved,and the average size of the matrix particles was about 30-70 nm.Compared with Ni/N-DLC(0.04 g/350mL)films,micro Vickers hardness of the Ni/N/MWCNTs-DLC(0.06 g/L)film was increased by 11.21%.In addition,the friction coefficient and wear loss of the Ni/N/MWCNTs-DLC film possessed the minimum,which were 0.146 and 1.40×10-5 kg/m,respectively.