Study On The Preparation And Mechanical Performance Of Diamond Film On The Surface Of Cemented Carbide With Buffer Layer

Diamond film deposited on the surface of cemented carbide tools with chemical vapor deposition method combines the mechanical properties of cemented carbide and diamond film, and could be a kind of ideal tool material to lathe composite materials, nonferrous metals, alloys and so on. However, the binder phase, cobalt, has a seriously negative impact on the nucleation and growth of diamond film, because the carbon has a great solubility coefficient and a high diffusion coefficient in the Co binder phase. What’s more, cobalt also promotes the growth of graphite, greatly reducing the adhesion property of diamond films. The negative impact of Co has become a major obstacle to restrict the large-scale and industrial application of diamond-coated carbide products.In this paper, we combined the chemical etching and buffer layer methods, namely the removal of Co and isolation of Co, to eliminate the negative impact on the nucleation and growth of diamond films. Four kinds of buffer layers, Ti N, Ti C, Cr N and Si N, were prepared respectively on the surface of cemented carbide after chemical etching by magnetron sputtering. The diamond films were deposited on the surface of buffer layers by hot filament chemical vapor depositionThe structural and morphologic analysis of substrate, buffer layer and diamond film demonstrated that chemical etching could remove the binder phase on the surface of cemented carbide and that diamond film has been deposited on the surface of Ti N, Ti C, Cr N, and Si N buffer layer successfully. According to the buffer layer whether has a reaction with substrate or diamond film, four kinds of buffer layers could be grouped into three types, i.e. reaction with diamond, reaction with substrate and nonreaction with diamond and substrate. The diamond films with Ti N and Cr N buffer layer, which belong to the type of reaction with diamond, showed a better film quality and contained a higher amount of sp3 bond, while the diamond film with Ti C buffer layer, which belongs to the type of reaction with substrate, contained a general amount of sp3 bond. And diamond film with Si N buffer layer, which belongs to the type of nonreaction with diamond and substrate, showed a poor film quality and contained a lower amount of sp3 bond.The microscopically mechanical properties of substrate, buffer layer and diamond film were studied by in-situ nanomechanical testing system, suggesting that the diamond films with four kinds of buffer layers had high micro-hardness and elastic modulus, and the micro-hardness was inversely proportional to the friction coefficient for these four kinds of buffer layers.The influence of chemical etching time and buffer-layer thickness on the adhesion strength of composite film(buffer layer/diamond) was analyzed by Vickers hardness testing system. The diamond film with Ti N buffer layer did not peel off after the Vickers hardness test, and the adhesion strength of Ti N/diamond composite film was affected by chemical etching time and buffer-layer thickness simultaneously. However, the failure of diamond film with Ti C buffer layer occurred in the interface between Ti C and diamond film, and the adhesion strength of Ti C/diamond composite film was also affected by chemical etching time and buffer-layer thickness simultaneously. For the diamond film with Cr N buffer layer, the adhesion strength of Cr N/diamond composite film was strongly dependent on the buffer-layer thickness and the failure occurred in the interior of Cr N buffer layer. The diamond film with Si N buffer layer had a large area damaged and the failure occurred in the interface between Si N and diamond film.Friction and wear test at room temperature showed that the antifriction and anti-wear property of the Ti N/diamond composite film was better than that of the Ti C/diamond, Cr N/diamond and Si N/diamond composite films.Above all, optimum pretreatment process was 10-min chemical etching and 800-nm thick Ti N buffer layer. The diamond film coated on the surface of cemented carbide tools prepared by optimum pretreatment process had a good film quality and dense grains. No significant graphitization occured.