Design And Preparation Of Tetrahedral Amorphous Carbon Films And Study On Their Tribological And Electrochemical Corrosion Behaviors

Tetrahedral amorphous carbon(ta-C)with smooth surface and compact structure possesses excellent mechanical properties and chemical stability,showing a broad application prospect in friction,electrochemistry and other fields.However,the anti-friction and anti-wear characteristics of ta-C film are facing great challenges under complex and harsh working conditions.For example,the mechanical components of ship and hμman implanted medical devices are facing the combined effect of friction and corrosion,thermal assisted magnetic storage and precision glass forming are affected by friction and high temperature at the same time.In this dissertation,the design and preparation of high-quality ta-C films for harsh working conditions were carried out,and the relationship among the microstructure,atomic bonds,multilayer structure and friction,high temperature,electrochemical corrosion properties of the films was explored,and the design criteria of high-performance ta-C films was proposed.The comprehensive properties of ta-C film,such as friction,corrosion and high temperature stability,were studied under complex working condition.(1)The dependence of electrochemical behavior upon the microstructure and atomic bonds of hydrogenated diamond-like carbon(DLC:H)film and ta-C film were comparatively investigated.The corrosion resistances of ta-C film with thickness of 20nm and 40 nm were superior to DLC:H film with thickness of 1.1μm.Despite the larger thickness,DLC:H film exhibited poor sealing effect and limited corrosion protection due to hydrogen existence,high sp~2clusters and porosity density.The high sp~3 content and low porosity of ta-C film endowed it with good barrier to penetration of corrosion media.Noted that the ta-C film with 20 nm thickness failed to prevent the pitting phenomenon of 316 stainless steel.(2)Taking into account of the advantages of filtered cathodic vacuμm arc(FCVA)technology and the concept of"high throughput preparation"of materials,we prepared a series of ta-C films with similar structure but different thickness,by adjusting the plasma flux and the deposition position.The I_T/I_G values of ta-C films with different thicknesses showed dispersion distribution.Despite of the thickness changes,both the dispersion values Disp(G)and the size of sp~2 clusters maintained relatively stable.Moreover,the sp~3 content of ta-C film was about 55±5%,regardless of the thickness changes.The nano-tribological behavior of ta-C films was mainly affected by the surface morphology,while the electrochemical behavior remained unchanged due to the stable sp~3 content.The influence of glancing angle deposition on the microstructure and properties of ta-C film was further investigated.The results showed that glancinng angle deposition effectively reduced residual stress(29%)at the sacrifice of slight deterioration of sp~3 content(13%)and hardness(19%).The porosity,roughness,contact angle and surface dangling bonds of ta-C films also could be tailored by the incident angle of carbon ions(0°～75°).The content of sp~3,sp~2 clusters and surface properties of the ta-C film were the predomintary factor to its electrochemical corrosion characteristics.The optimal electrochemical corrosion resistance was obtained at the incident angle of 45°.(3)The introduction of interface and low-stress buffer layer was realized by constructing multilayer structure,where the soft and hard sub-layer were designed alternatively.The multilayer structure reduced the residual stress of ta-C film and restrained the spalling.The effects of the composition of the adjacent sublayers and the modulation period on the microstructure,friction and electrochemical corrosion properties of the multilayered ta-C films were studied.The four period multilayer ta-C film with alternating bias voltage of-150 V and-50 V was selected.The difference in wear resistance of multilayer ta-C films could be related to mechanical properties,in which high hardness and H/E value contributed to low wear rate.The existence of micro-defects such as through pores in the film provided a rapid diffusion channel for corrosive media,which limited the electrochemical corrosion protection of the multilayer ta-C film.Adding a thick gradient transition layer to the multilayer ta-C film was not enough to improve the corrosion resistance.(4)The properties of multilayer ta-C film under complex working condition were studied.The multilayer ta-C film was insensitive to environmental hμmidity.Moreover,the multilayer ta-C film showed higher wear resistance and longer wear life in 3.5 wt%Na Cl solution compared to the dry friction case.After deposition of multilayer ta-C film,the corrosion resistance of the substrate was enhanced by an order of magnitude and the polarization resistance was increased by 20 times.The multilayer ta-C film effectively reduced the friction coefficient and wear rate of the substrate,and the electrochemical properties remained stable before and after tribocorrosion,revealing a good tribocorrosion resistance.In addition,the high temperature tribological behavior of the multilayer ta-C films under different loads(1-5 N)and temperatures(400-600°C)was investigated.Results showed that the multilayer ta-C films exhibited excellent friction properties of high temperature under low load.In order to improve the tribological behavior at high temperature and high load,the multilayer ta-C film thickened with the top layer was further fabricated.The sample with hard top layer obtained the low friction coefficient of 0.11 and low wear rate at load of 2 N,500°C.The analysis showed that graphitization was harmful to high temperature antifriction and lubrication,but a sp~3-rich top layer improved the high temperature friction performance of multilayer ta-C film.