DLC (Diamond Like Carbon) as a hard carbon film has such features as the lowest friction coefficient among various ceramics coating materials, high hardness, and less aggressiveness to other parties. Because of these features, its practical use for sliding is in progress. However, people now call other films DLC too even though they are different from those defined in ‘80s. Moreover, new manufacturing methods such as spatter method and arc method are now used in addition to the conventional ones like radio frequency (r.f.) plasma assisted chemical vapor deposition (PACVD) and ionized deposition.

Another topic in these days is a flexible DLC film that uses rubber as radical material in stead of the formally used radical materials such as metal and ceramics. We thought that three issues have to be resolved. (1) Low heat resistance of the polymer materials such as rubber and resin. (2) Pollution of the polymer material surface by oil, fat, resin, and oxidation prevention agents, etc., and (3) Transformation of the polymer materials. To resolve these possible problems: (1) We have developed a processing method by using the Amplitude-Modulated RF Plasma Chemical Vapor Deposition method which enables coating at lower temperature (below 80 degree C) and does not allow the processing temperature to rise any higher. (2) To prevent the pollution, we decided to clean the polymer surface by plasma. (3) To prevent the transformation, the film should be flexible enough to absorb the polymer material transformation. We have modified the DLC film structure to permit expansion and contraction. This new DLC film is applied as a coating of ‘O’ ring for 35 mm zoom camera.

This paper reports a technological trend of various applications of the recent DLC films and an example of sliding use of the ruber radical material.

DLC coatings with excellent tribological properties have attracted much attention in the automotive industry. Friction control of automotive sliding parts and dry machining without lubricants have become more important for energy saving. DLC coating is one of the key technology for them. However, conventional DLC coating is not widely used in the automotive industry because of their low productivity and adhesion of the coatings.

The new methods of the DLC-Si (silicon-containing DLC) coating by DC-PACVD, and improving of adhesion of the coating were developed in our laboratory. The throwing power of the new coating method is excellent compared with that of sputtering or RF-PACVD, and the coating for the parts loaded in three dimensions is possible. The large-sized DC-PACVD equipment (φ800x1500mm) for DLC-Si coating was designed, and DLC-Si coatings in large scale production was investigated.

In this report, it will be revealed that the new coatings and the productivity of the coating method newly developed have enough potential for application to automotive industry.

Diamond-like carbon films are well known for their outstanding tribological properties, which has been shown in many studies. Because of their extreme hardness, low coefficient of sliding friction (often after some running-in time) and especially their ability to form a transfer layer on the counter-body of the frictional pair these coatings have found many areas of application. There are many different types of these coatings on the market depending on the deposition process and on the deposition parameters used. This variability allows to tailor certain film properties to specific applications. Additionally, alloying with different elements allows further adaptations.

One special tribological problem is found in applications where almost no or only little motion takes place and therefore no transfer layer can build up. In this case a special coating is needed which has a low coefficient of friction already at the very beginning of any motion. A similar situation is found in low load applications where neither a transfer layer is created nor the transformation of the topmost surface layer into a more graphitic-like state takes place.

In this study silicon containing diamond-like carbon films are produced in a r.f. plasma-activated chemical vapor deposition system. A mixture of acetylene and an organosilicon gas is used to deposit silicon containing diamond-like carbon films onto hardened steel sample plate. On top of a supporting coating a 20 nm thick diamond-like carbon layer with varying silicon content is deposited using different selected self-bias voltages.

The coefficient of static friction against a hardened stainless steel surface is then measured in dependence of the silicon content and of the self-bias used. The films display a constant coefficient of static friction even after many single measurements. The results are compared to results obtained for pure diamond-like carbon films.

Analogously to the way as hard ceramic coatings (i.e. TiN, TiAlN,…) became essential in the field of cutting tools, hard low-friction coatings (i.e. diamond and diamond like carbon coatings) are now becoming more and more important in the field of machine components. By both improving the wear resistance and giving excellent frictional properties, hard low-friction coatings certainly provide a great opportunity to improve durability and to reduce frictional losses of machine components. However, the demands on coatings for machine components are tougher than those on cutting tools. The expected life time is very long, both contact surfaces are of the same importance, the substrate hardness is rather low, and further the presence of the lubricating oil, originally designed for the steel/steel contact situation makes the selection and design even more complicated.

The aim of the present work was to investigate the tribological behaviour of DLC coated surfaces, operating under different lubrication regimes. Tests were performed in a pin-disc and a load-scanning test rig, where DLC (WC-C) coated samples were loaded against coated and uncoated ones, while the steel/steel combination was used as a reference. All material combinations were tested under starved, boundary and EHD lubrication conditions, using four lubricants; pure poly-alpha-olefin oil (PAO), PAO mixed with commercial sulphur-based EP additive or ZDP-based AW additive, and fully formulated gearbox oil. Results of the investigation will be presented by means of the coefficient of friction, monitored as a function of time and load, wear and analyses of worn surfaces.