Medical grade ultra-high-molecular-weight- polyethylene (UHMWPE), which articulate well against metal, typically Co-Cr-Mo alloy, is commonly used in total joint replacements. The clinical performance of the components made of UHMWPE, is considered very good except for the concern about their wear. The adverse tissue reaction due to these wear particles is found to be the major factor responsible for the loosening or failure of the implant. Development of new and/or improved material pair, which produces least wear, is one of the solutions for a long lasting orthopedic implant.

Diamond-like carbon (DLC) coatings have received enormous attention as a wear resistance coating, due to its high hardness. In addition to that, DLC coating has many other superior properties as an implant material such as biocompatibility and chemical inertness. The properties of DLC coatings can vary widely depending on the deposition technique as well as the deposition parameters. The filtered cathodic vacuum arc (FCVA) technique has been proven to be an efficient method of producing high quality DLC coatings. Some studies claim that the DLC coated stainless steel sliding against the same reduces the wear rate to a very low value. However, any incidental failure of the coating can cause drastic friction and wear. Hence the present study focuses on the surface modification of the existing implant materials. The tribological characterization of Co-Cr-Mo alloy with and without DLC coating sliding against UHMWPE counter-surface in different tribological environments such as ambient air, DI (de-ionized) water and SBF (simulated body fluid), is discussed in the paper. It is observed that the DLC coating improves the wear resistance of CCM alloy to about 10 times and hence such coating can be used to improve the life of artificial joints. The influence of surface roughness on the characteristics of the DLC coatings has also been investigated.

Polycrystalline and smooth fine-grained diamond (SFGD) coatings are deposited at 600°C on Ti alloys or Ti-coated surfaces by a two-step microwave PACVD procedure using CO-H₂ or CO₂-CH₄ during the second step. Optical emission spectroscopy and mass spectrometry reveal important differences between the plasma species produced in the different conditions including the deposition from CH₄-(Ar-H₂). SEM, AFM, XRD, TEM, visible and UV Raman spectroscopy allow to characterize the surface roughness, the diamond quality (sp³/sp² ratio) and the microstructure of the coatings. The roughness can be decreased from about 120 nm (r.m.s.) for polycrystalline coatings to 35 nm for SFGD coatings while the incorporation of sp²-hybridized carbon is only slightly increased. It can be further lowered to the 30-15 nm range while the sp²-carbon incorporation increases. Note that this low roughness is independent of the coating thickness due to the microstructure.

The difference of microstructures and diamond purity influence the hardness and Young's modulus of the coatings, measured with an ultra-low load micro-indenter and by Brillouin scattering. The residual stresses are deduced from the Raman spectra.

Finally the tribological behavior in ambient air of 100Cr6 steel, uncoated and diamond-coated Ti-6Al-4V alloy sliding against all coating types including some polished polycrystalline coatings has been studied with a rotating pin-on-disk tribometer. The strong influence of the surface roughness has always been evidenced. The counterface materials present however different tribological behaviors which also depend on the diamond quality. Different friction and wear mechanisms are discussed as a function of these parameters. The advantages of SFGD with respect to polycrystalline coatings are emphasized. Very low wear rates of the alloys and low friction coefficients, in the 0.05 - 0.1 range, were obtained for the smoothest coatings, even under fairly heavy load.

The technological evolvements over the last decade highlighted the importance of the machining ; its use, always increasing, leeds to the necessity of its cost lowering, that means a pieces tooling at very high speed and directely in final surface state.

A low wear rate combined with an extreme hardness are two of the excellent mechanical properties of the diamond and DLC coatings which make them suitable for machining, and more particularly for coated the cutting tools.

It was then interesting to study whether diamond and DLC coatings can present lubricating characteristics in these kind of applications.

The tribological behaviour of the diamond/DLC couple was consequently studied : diamond was obtained by flame process whereas DLC coatings were deposited on steel discs by dc-CVD process ; these coated discs were then submitted to an atomic hydrogen bombardment.

The friction tests were realised under vacuum and hydrogen ; the role of the atomic hydrogen on the surface modifications and on the transferred layers formation as well as its influence on the friction coefficient were clearly shown.

Scanning Electron Microscopy observations and Energy Dispersive Spectroscopy analyses were used to reveal the surfaces changes ; Raman Spectroscopy was carried out to highlight the coatings evolution.

Free-standing diamond layers can be produced in large sizes by various deposition methods: microwave, radio-frequency and combustion flame etc.,.

The advantage of the combustion flame method is to obtain high growth rates of diamond deposition, however the poor uniformity of thickness that has not yet solved.

In this paper, free-standing diamond films are deposited using combustion flame method on polycrystalline copper substrates.

Studies on the nucleation and growth of diamond show that copper is a promising substrate material for the free-standing diamond films preparation.

By use the "trumpet bell" welding torch developed by ERMES group has made possible to deposit diamond on large area with very good uniformity.

In our experiments, high quality free-standing diamond films of 30-40 µm thickness and of 10 mm diameter were obtained after 20 minutes deposition. The quality and the uniformity of the free-standing diamond films are observed by Scanning Electron Microscopy (SEM) and analysis by Raman Spectroscopy (RS); profilometry.

The four points probe method is also used to measure the resistivity of the film as a function of the temperature (?-T) during the heating and cooling phases to the room temperature (RT).