| Recently,GLC films have attracted much attention due to its outstanding properties,including high hardness,anti-corrosion property,and superior lubricating property.The remarkable intrinsic properties make GLC films appropriate to be protective films for improving tribological properties of marine frictional equipments.However,when sliding under marine environment,the synergetic effect of wear and corrosion often causes failure of GLC,which limits its practical application.It is an effective method to improve the mechanical and tribocorrosion properties of films by design of components and structure.In this thesis,to satisfy the imperious demands of high performance protective coatings for marine frictional equipments,serial GLC films with various metal buffer layer/interface,multilayered structure and top-layer functional layer were designed and prepared.Then the service behavior of optimized GLC films was deeply investigated in the“immersion-tribocorrosion”conditions under artificial seawater.The relationship between film structure and properties was established by systematical analysis and in-situ electrochemical tests during tribocorrsion tests.The results provide fundamental guidance for the design and development of high performance carbon films in kinds of marine equipments.Firstly,various metal buffer layers?Cr,Ti,W?were chosen according to the different bonding character of the C atom with metal atoms.Then the different metal buffer layer/interface structural films containg Cr/GLC,Ti/GLC and W/GLC were prepared by direct current magnetron sputtering technology.The effect of metal buffer layers on microstructure of interface and bond states of GLC films were carefully surveyed by EELS.Based the EELS results,the tribological properties of Me/GLC films in artificial seawater were investigated.Results show that,as opposed to the Ti/GLC and W/GLC film,the Cr/GLC film has highest sp2 hybridization bond contents,and sp2 content increases from the top layer to Cr/CLC interface.The highest sp2 contents promote graphitization degree of the transferred tribo-film,which acted as lubrication medium in tribological process.According to the curves of potentiodynamic polarization,the Cr/GLC film manifests the superior anti-corrosion properties with Ecorr of-0.16 V and icorr of 4.42×10-99 A/cm2.Therefore,the Cr/GLC film shows the outstanding tribological properties under artificial seawater.Based on the previous research for optimized Cr buffer layer,Cr/GLC films were prepared with different thickness ratio?1:2,1:3,1:5,1:10,1:20?of Cr and GLC films.Then the effect of thickness ratio on microstructure,mechanical and tribological properties under artificial seawater was systematically studied.Results show that the monolayered Cr/GLC film with optimized thickness ratio of 1:3 performs the best tribological properties with the average friction coefficient of 0.059 and wear rate of 6×10-88 mm3/Nm.The formation of channel for electron exchanging is originated from the propagation of intrinsic defects and the gaps formed by depth crystalline evolution.Eventually,the failure and flaking off of the Cr/GLC film is accelerated with the effect of wear and corrosion synergistically.Designing the multilayered structure can increase toughness of the film as much as 13%.By inhibiting the formation of channel for electron exchanging,Rp?polarization resistance?of the film is increased to 1.1×107?cm2 with superior anti-corrosion property.Then the multilayered Cr/GLC film demonstrates a lower wear rate of 2.3×10-8 mm3/Nm in artificial seawater with increased toughness and anti-corrosion properties.To improve the tribocorrosion properties of films,Cr/GLC multilayered films with different modulation period of 1000 nm,500 nm,333 nm and 250 nm were fabricated on 316L stainless steels and the tribocorrosion properties were studied.Results indicate that both the G peak and ID/IG ratio vary in a small range of 1552 cm-1 and3.13 as the modulation period of the Cr/GLC film decreases from 1000 to 250 nm.The hardness and the H3/E2 value of the Cr/GLC multilayered films increase with decreasing modulation period,the toughness of the film can be increased as much as23%via multilayered structural design.A maximum hardness and H3/E2of 20.03±0.59 GPa and 0.241 are achieved for the Cr/GLC film with a 250 nm bilayer thickness.The Nyquist and Bode plots show that the polarization resistance?Rp?firstly increases and then drastically decreases as the modulation period decreases from 1000 to 250nm.The Cr/GLC film with a 250 nm bilayer thickness completely peels from the substrate,which ascribed to the increase of structural defects caused by thinner top layer amorphous carbon by analyzing the Mott-Schottky plots.By taking top-layer thickening strategy for the Cr/GLC film with 250 nm modulation period,the tribocorrosion performance is significantly enhanced to the friction coefficient of0.045 and the wear rate of the 3.17×10-7 mm3/Nm.Taking into account the unavoidable intermittent service accompanying long-time immersion in seawater,the immersion time was controlled from 4 h to 48 h in artificial seawater and its effect on the tribocorrosion behavior of the Cr/GLC multilayer films was investigated.Results show that the average friction coefficient of the Cr/GLC multilayered film continuously increases from 0.070 to 0.085 with prolonged immersion time,while wear rate firstly decreases and reaches its minimum value of 5.20×10-7 mm3/N m at 12 h,then gradually increases as the immersion time is in the range of 24 h to 48 h.Electrochemical impedance spectroscopy?EIS?analysis,before and after the tribocorrosion test,demonstrates that the corrosion resistance of the Cr/GLC multilayered film mainly associates with the competitive effects of corrosion products blocking the micropores and contact stress promoting micropores propagation.Comparative EIS measurements in 4.6 wt.%NaCl solution indirectly indicates that the formation of calcium and/or magnesium compounds is responsible for the immersion time-affected tribocorrosion and corrosion performance of the Cr/GLC multilayered film in artificial seawater. |
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