Study on Preparation and Tribocorrosion and Lubrication Mechanism of TC4 Titanium Alloy Surface Hard Film

Author:Cao Lei

Supervisor:wan yong


Degree Year:2019





With the rapid development of clinical medicine,people’s expectations for medical level are getting higher and higher,which requires artificial joints made by titanium alloy to have longer service life and higher running stability when used in the complex environment of human body fluids.On the other hand,in today’s automobile development towards light weight,environmental protection and energy conservation,titanium alloy is undoubtedly the most potential material for key automotive engine components.However,it must be pointed out that titanium alloys are mostly used in structural materials in the industry at present.In addition to their disadvantages such as high price,poor formability and poor welding performance,another reason that can not be ignored is that titanium alloys exhibit poor tribological properties which severely limit the use of titanium alloys as key moving parts in machines.The surface modification treatment of titanium alloy can effectively improve the tribological properties under human body fluid and oil lubrication,prolonging the service life and improving the reliability of the operation of components made by titanium alloy.Based on this,a thermal oxide film and a DLC film were prepared on the surface of titanium alloy,and the two layers were organically combined to construct a two-layer composite film.The corrosion resistance and lubrication properties of the film were studied,and the antifriction and antiwear mechanism was discussed.The paper has the following main conclusions:(1)The surface deposited Cr/CrC/DLC gradient transition film system can significantly improve the corrosion and wear resistance of TC4 titanium alloy in simulated artificial body fluids.The Cr/CrC(40)/DLC film system prepared by high C2H2 flow has a CrC transition layer which is transformed from a columnar crystal structure to an amorphous/nanocrystalline structure.This improves the hardness of the transition layer,reduces the internal stress of the film and improve film base bonding strength.At the same time,the amorphous/nanocrystalline structure of CrC has more grain boundaries,which can effectively inhibit the initiation and diffusion of cracks in the friction process,delay the corrosion of the TC4 titanium alloy substrate in the corrosive medium,and thus exhibit excellent corrosion and wear resistance.(2)The effects of temperature and time of thermal oxidation treatment on the structure and corrosion resistance of oxidized film on the surface of TC4 titanium alloy samples were investigated.In the experiment,it was found that in the simulated artificial body fluid,the corrosion resistance and corrosion wear resistance of the sample after thermal oxidation did not increase with the increase of the thermal oxidation temperature or the prolongation of the thermal oxidation time.In the temperature and time range of the study,the samples,obtained by thermal oxidation treatment at 700oC for 5h,have better surface hardness,more dense membrane structure,better membrane-based bonding performance,exhibiting optimal corrosion and corrosion resistance resistance in simulated artificial body fluids..(3)Polytetrafluoroethylene(PTFE)and DLC films were deposited on the surface of TC4 titanium alloy oxide film after thermal oxidation treatment by dip coating and chemical vapor deposition,respectively.The double-layer composite film system was obtained.On the one hand,the surface film closes the defects of the oxide film,effectively increases the density of the coating,prevents the contact of corrosive ions with the substrate and improves the corrosion resistance by their good hydrophobicity.On the other hand,the surface film has good lubrication properties.Therefore,the corrosion resistance and corrosion resistance of the two-layer composite film in the simulated artificial body fluid is significantly improved,as compared to the pure thermal oxidation sample.(4)Under the lubrication condition by a fully formulated oil,the TiO2 layer formed on the surface of the thermally oxidized TC4 titanium alloy sample improves the surface hardness,reduces the adhesive wear,improves the surface wettability,and promotes the anti-wear in the lubricating oil.The additive undergoes a tribochemical reaction on the surface to form a phosphate boundary film which has antifriction and wear resistance,and thus exhibits excellent tribological properties.(5)Based on the photocatalytic performance of TiO2 layer on the surface of TC4titanium alloy by thermal oxidation,the in situ catalytic degradation of lubricating oil molecules in the friction process during the friction process,which builds DLC film in the contact zone to reduce the friction and wear,is firstly proposed.The design idea is systematically investigated to study the anti-friction and wear-resisting mechanism of polyalphaolefin(PAO6)molecules which are degraded on TiO2 surface to form DLC coating.