Fabrication And Tribological Properties Of DLC Films Deposited By MF-PCVD

Diamond like carbon (DLC) films were prepared by middle frequency plasma vapor deposition method from different hydrocarbon source gases at varying voltages using the plasma chemical vapor deposition system. The source gases used were the unsaturated hudrocarbon C₂H₂ and CH₄ mixtured with hydrogen.Firstly, DLC films were deposited on Si substrates by different deposition parameters. The films'thicknesses were measured by scanning profile method, and then the deposition rates were obtained. Chemical structure and surface morphology were investigated by laser Raman spectroscopy (Raman) and atomic force microscopy (AFM). Nano indenter was used to determine hardness and modulus of DLC films. We tested the thermal stability of the film by annealing in the vacuum. The inner stress is tested by Residual Stress tester. Tribological behavior of DLC films have been investigated by ball-on-disk tribometer in normal laboratory, and the grinding crack were microexamed by metallographic microscope. We analysed the film's friction mechanism.The Raman shows that we prepared the DLC: H. When the C₂H₂/H₂ ratio is 6/6 or 6/12, the deposition rate increases and then declines as the voltage increases. While the C₂H₂/H₂ ratio is 6/18, the deposition decreases as the voltage increases. As the voltage increases or the H₂ ratio in the hydrocarbon source gases increase, the H content in the films decreases, sp² phase organized in rings changes to organize in aromatic rings and the ring-like sp² clusters grow up. Especially for the C₂H₂/H₂ is 6/18, the film changes to graphitization obviously with increasing the voltage. The hardness of DLC films ranges from 7GPa to 17.5GPa and the maximum elastic modulus is about 145GPa. The thermal stability temperature is 300℃.While the source gases were the saturated hydrocarbon CH₄ or CH₄/H₂, the deposition rate increases with the voltage increasing. As the voltage increases or the H₂ ratio in the source gases increase, the H content in the films decreases. The sp³ content is high, but most sp³ sites are bond to hydrogen. As the voltages increases, the C-C sp³ bonding is increasing, leading that the hardness and modulus increase. The residual stress also increases as the voltage increases.The friction coefficient of DLC films deposited on GCr15 decreases from 0.23 to 0.15 as the voltage increases, the grinding crack broadened. When the source gases were mixtured with H₂, the friction coefficient also decreases. The friction coefferent is indepent of the thickness of the DLC films, but the thicker film has more friction stability. The friction behavior of the DLC films is mainly infuluenced by the H content and sp²/sp³ ratio.