Synthesis,Structure And Tribological Properties Of Titanium/Aluminum Co-doped Diamond-like Carbon Based Films

Diamond-like carbon?DLC?film is a kind of amorphous carbon material composed of sp³-C and sp²-C.Because of its high hardness?wide optical transparency and abrasion resistant,DLC films have widespread application in many industrial areas.However,the high rssidual compressive stress,low adhesion to substrates and unstable friction behaviors with different environment of the DLC films limit its applications.Incorporation of metals is a simple and most effective method to solve the problems;while single element doping is hard to satisfy the complex and changeable conditions in practical applications.It is necessary to obtain DLC films with high hardness?low residual stress?low coefficient?high reliability?long-period.And doping different metal elements into DLC provide an effective method to improve the combined properties due to the synergistic effect of different metals.Based on the theoretical results,Ti/Al co-doping DLC?Ti/Al-DLC?films is studied systematically.First,we fabricated the Ti/Al-DLC films with different metal contents(Ti_0-13.0%,Al_0-13.3%)through adjusting the sputtering current?bias?source gas by hybrid ion beam deposition system.The result shows that residual compressive stress and hardness decreased following the increasing of metal contents.With low contentrations?Ti<10.1%,Al<4.8%?,dissolved metal atoms in DLC matrix could play as pivotal sites,whereby the distortion of the bond angles and bond length can occur susceptibly,and the residual compressive stress was decreased about 74%and the hardness decreased about 4.8%;with the increasing of metal composition,Ti atoms tend to bond with C atoms and form carbide nanoparticulates,the microstructure of films were nanocrystalline/amorphous composite structures,which consequently caused reduction in residual stress by grain boundary sliding and diffusion and the hardness was improved because of the exsidence of carbide.With the increasing of metal contents,the sizes and amounts of carbides are improved,and contents of sp³-C are increasing,which leads to the increasing of hardness and residual compressive stress.In order to improve the compatibility of Ti/Al-DLC films with different substrates,Ti/Al interlayer was added between DLC films and stainless steel substrates.And the properties evolution of DLC films after adding the interlayer was studied.The results show that the addition of the interlayer can effectively reduce the residual stress?1.03 GPa to 0.25 GPa?,and increase the adhesion of the film?60.5 N to 67.2 N?.The amounts and area of the peelings around the scratches reduced because of Ti/Al interlayer,the bearing capacity of Ti/Al-DLC was improved.The tribological behavior of the Ti/Al-DLC film with interlayer under the atmosphere and the PAO oil environment was characterized.It was found that the films both showed excellent tribological properties.Under the atmosphere,the low shear force transferlayer was formed in the contact interface,which leaded to the lower friction coefficient of 0.05 than that of 0.11 under PAO.But the wear rate of Ti/Al-DLC films was 2.68×10^-17 m³N^-1m^-1 under PAO,it was much lower than the wear rate under the atmospheric environment of 1.56×10^-16 m³N^-1m^-1,the existence of grooves in friction pair could store the PAO oils,and hydraulic oil film was formed to avoid the direct contact between the friction pair in thetribological process.Finally,based on the interlayer optimization parameters,the antifriction lubrication mechanism of Ti/Al-DLC under atmospheric conditions are studied in depth.The results exhibit the films deposited at 2.5A exhibited the lowtest friction coefficient of about 0.05 and wear rate of1.56×10^-1616 m³N^-1m^-1.This attributed to the high level graphitization of wear tracks and the formation of containious and compact transfer layer.Especially,the thickness of transferlayer is 3?m.The translayer was segregated obviously and structure was different from deposited films,which could be described as dual or hierarcy nanostructure constructed of cross-linking amorphous carbon networks and hard phase?mainly TiC and Al2O3?structure.Energy tend to release because of the the special structure which are easy to shear,and metal carbide or oxide films can prevent invasion and destruction of carbon network by O in the air,greatly improved the oxidation resistance of DLC film,which leads to the excellent tribological properties of Ti/Al films.