Abstract
Non-hydrogenated diamond-like carbon (DLC) films with various ratios of sp3/sp2 were prepared on cemented carbide YG8 with DC magnetron sputtering technology. A pure graphite target was selected as the carbon source. Before DLC deposition, a surface etching pretreatment was carried out by mid-frequency magnetron sputtering method, using Ti atoms to improve adhesion strength. The ratios of sp3/sp2 were adjusted by bias voltages. In order to investigate the effect of the ratio of sp3/sp2 on adhesion and tribological properties, Raman spectra, XPS spectra, adhesion scratch test and ball-on-disk dry friction tests were applied. The results indicated that the ratio of sp3/sp2 fluctuated with bias voltage, increasing in the range of 0.74 to 0.98. The adhesion strength decreased from 31.5 to 18.4 N with the increasing ratio of sp3/sp2, while the friction coefficient rose in DLC-Si3N4 and dropped in DLC-Ti6Al4V. For DLC-Ti6Al4V, the oxidation of Ti6Al4V had a greater influence than graphitization of DLC. The hard oxides of Ti6Al4V broke the graphite transfer layer leading to a high friction coefficient. The wear rate was approximately linearly related to bias voltage. The coefficients of the linear regression equation were influenced by different friction materials. The adhesion strength and the friction coefficient were fitted as a function of the ratio of sp3/sp2.
Highlights
Diamond-like carbon (DLC) film is a type of metastable amorphous carbon film, composed of sp3 and sp2 hybrid carbon atoms
Results and Discussion increases with the ratio of the intensities of the D and G peaks (ID/IG) decreasing, G peak position moving towards a lower wave number and the full width at half maximum (FWHM) of G peak
With the2negative bias voltage increasing to 300 V, the ID/IDLC
Summary
Diamond-like carbon (DLC) film is a type of metastable amorphous carbon film, composed of sp and sp hybrid carbon atoms. The adhesion strength, friction coefficient and wear rate are the most direct indexes used to reflect the properties of DLC films. The hardness and adhesion of hydrogenated DLC film are closely correlated to the ratio of sp bonding [14,15]. Under oil-lubricated conditions, the hydrogen-free DLC films with lower sp content show higher friction coefficients. Oxidation of some materials like aluminum alloy has been proven to affect the friction coefficient and wear rate of DLC film [17,21,22,23,24]. High substrate bias voltage produces better adhesion to DLC films and leads to lower hardness and poor wear resistance [33]. The research substances are similar, the influence of bias voltage differs because of the difference in composition and structure of DLC films, such as the ratio of sp3 /sp. With the ratio of sp3 /sp in a certain range, the effects of the ratio of sp3 /sp on the adhesion and tribological properties of DLC films were studied quantitatively
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