Surface Modification of Titanium by Plasma Assisted Chemical Vapor Deposition (PACVD) Methods

Abstract

One way of obtaining new materials with different properties is to modify existing ones to improve their insufficient properties. Due to the fact that many of the useful properties of materials, including wear and corrosion resistance, friction coefficient and biocompatibility, depend on the state of the surface, modern surface engineering methods are especially helpful. They involve the deposition of the layers with tailored chemical composition and structure. In terms of medical applications, amorphous or nanocrystalline layers containing carbon, nitrogen, silicon and hydrogen appear to be the most suitable. They combine the beneficial properties of silicon carbide SiC and silicon nitride Si3N4, and thus exhibit a strong resistance to oxidation at high temperatures, high modulus of elasticity, low friction coefficient and wear resistance. However, silicon carbonitride compound is not stable thermodynamically in normal conditions and therefore it must be obtained by non-conventional synthesis. One of such method is Plasma Assisted Chemical Vapour Deposition (PACVD). The authors of this paper anticipate that the modification of titanium surface by SiCxNy(H) layers make them proper for use as materials for long-term contact with human body. It contains results of research on titanium Ti Grade 2 surface modification by deposition amorphous carbon layers doped with nitrogen (a-C:N:H) and silicon carbonitride layers SiCxNy(H). What is more, for IR analysis, in the same plasmochemical methods process obtain layers on monocrystaline silicon (001)Si. The layers were synthesis by PACVD with plasma generated by radio waves (RFCVD, 400 W, 13.56 MHz) for a-C:N:H layers and microwaves (MWCVD, 2 kW, 2.45 GHz) for layers containing silicon, carbon, nitrogen and hydrogen. During deposition process metallic surface were ion-etching by argon plasma. The layers were obtained from reactive gas mixture containing CH4, N2or NH3for a-C:N:H layers and CH4, SiH4, N2or NH3for silicon carbonitride compound. In this process argon was used as an inert gaseous. Process conditions allowing obtaining good adhesive layer to the metallic substrate were specified. Obtained systems were subject for further research. Chemical composition of the materials were studied by SEM / EDS techniques with application ETD and BSED detectors. Compared images registered for titanium before surface modification and surfaces covered by a-C:N:H or SiCxNy(H) layers. More information about layers structure provided FTIR spectroscopy. Spectra FTIR was register transmition for (001)Si-layer and reflective for titanium-layer systems. Assessed the impact of different kind of substrate on the layers deposited structure. Operational properties of synergic layer-titanium systems were evaluated in the measurements of tribological parameters. This tests shown that silicon carbonitride layers have the lowest friction coefficient and the highest resistance to wear. Furthermore, it was possible, on the basis of the obtained result, to indicate directions the surface modifications ensuring optimization on their usable properties as medicine and another industries. In previous authors paper the layers were investigated in the aspect of possible application in medicine.