Influence Of Buffer Layer On Structure And Performance Of Superhard Carbon Coating

Superhard carbon thin film (including diamond-like film and diamond film, etc.), has been used as one of the pop solid lubricants because of its superior tribological characteristics such as highest hardness and heat conductivity, low friction coefficient, and good chemical stability, and has obtained the widespread application. However, poor adhesion performance between film and substrate greatly limits the application of carbon film. This paper respectively applies buffer layer to diamond-like film and diamond film, discusses thickness of buffer layer effect on the properties of carbon films. The following results were obtained:(1) Cr buffer layers of six different thicknesses were respectively deposited on silicon substrate so as to constitute a series of Cr implantation layer/Cr buffer layer/ta-C films. SEM analysis suggests that the Cr implantation layer is favorable to improve the interfacial transition between ta-C film and Si substrate. X-ray diffraction detection reveals that the difference in thickness of Cr buffer layer does not significantly influence the crystalline structure. Additionally, Raman result shows the ductility of Cr buffer layer is favorable to remit stress of the ta-C layer. When the thickness of Cr buffer layer is increased, its corresponding nano-hardness value is decreased. However, its elastic modulus and adhesion exhibits an initial increase followed by a decreasing fluctuation. Study shows superior mechanical properties for the ta-C film with200-nm-thick Cr buffer layer.(2) A series of TiC/diamond composite films were deposited on WC substrate by a two-step preparation technique including AIP deposition for different Ti buffer layers, and subsequent HFCVD deposition for polycrystalline diamond layer following the carbonization of Ti layers. X-ray diffraction detection reveals that the thickness variation of TiC buffer layer does not exert observable effects on the diamond crystalline structure; however, with the increasing thickness of TiC layer, degree of preferred orientation of TiC (111) plane decreases.(200) and (220) increases. TiC grain turned the preferred orientation growth from (111) to a competitive growth of (111),(200) and (220). SEM observation indicates that the preferable feature of surface grains was achieved in TiC/diamond composite film with277-nm-thick TiC buffer layer. Raman spectra display that the internal stress of TiC/diamond composite films can basically constant with the thickness variation of TiC buffer layer,(ⅱ) The TiC/diamond composite film with277-nm-thick TiC buffer layer exhibits the superior tribological properties with friction coefficient low to0.09, along with a good wear resistance.(3) The diamond film thick to160μm was synthesized using a7-μm-thick SiC interlayer in an HFCVD process. The7-μm-thick SiC interlayer offerings (a) a preferred interfacial transition from the carbide substrate to the film,(b) an excellent buffer for the Co diffusion so as to make the substrate pretreatment ignorable, and (c) a crystalline state of cubic SiC to provide favorable morphology for the growth of diamond crystalline. The thick diamond layer on which it grows film with residual stress as low as0.397GPa. The average COF in dry friction has been found at about0.134, whereas extremely low COF (0.0413) has been found in oil lubrication and relatively high COF (0.184) has been found in mortar.