The exceptional tribological properties of a low deposition temperature PVD carbon coating, Graphit-C, have been recently reported. This paper describes the latest development of this coating and particularly how, by an optimisation of the deposition parameters, it has been possible to obtain very hard coatings with extremely low specific wear rates.

The coatings have been deposited in a Closed Field Un-Balanced Magnetron Sputter Ion Plating (CFUBMSIP) installation. An extensive study of the deposition parameters (Ion current Density, working pressure, substrates bias, deposition rate) is reported. By finding the appropriate conditions of deposition, very hard carbon coatings (plastic hardness up to 4000 kg mm^-2) can be routinely deposited. Preliminary analytical results are presented in order to characterise such hard coatings: HRTEM, SEM, XRD and Raman analysis are some of the different techniques used for this work. Finally, some of the applications requiring such a hard, low wear and low friction surface treatment are reported and tribological test results which demonstrate that this coating will outperform the treatments currently used.

Today, special research activities are concentrated on optimizing coating properties for improving the performance of tools. (TiAl)N-based hard coatings are well known for their high microhardness even at elevated temperatures as well as for their good oxidation and wear resistance. Further improvements concerning chip removal can achieved by reducing friction in cutting.

In this paper the cutting performance of different coated carbide tools are investigated in turning and drilling of tempered steel. Influences of coating composition and roughness of coated tools are considered. Highlighted are effects of MoS₂- and WC/C-coatings on chip formation and contact conditions. Besides, influences of cutting as well as of cooling conditions are examined. Cutting forces and contact conditions are determined experimentally. Chip formation is analyzed by using a special device to interrupt turning processes. Wear phenomena are characterized by SEM and EDX. Variations of contact and load conditions are correlated with the determined wear mechanisms. Effects of soft coatings on cutting performance in turning and drilling are discussed.

Mechanical seals are the predominant type of seals found on a wide range of pumps, mixers, compressors and other similar machines within the fluid handling industries. The performance of the seal, and therefore in turn, the performance of the particular machine, is determined by the sealing interface and the interface materials used. Indeed, the bulk and tribological properties of the mating materials are fundamental to the performance of a mechanical seal.

The present 'state-of-the-art' seal face combination is a high duty carbon-graphite material mated against a reaction bonded, or alpha sintered silicon carbide. Whilst this combination allows high duty specifications to be met, there are increasing demands from new applications for improvements in performance and reliability beyond that which can be achieved with current materials. Consequently, seal designers have identified the need to utilise surface engineering techniques to meet future requiremnts. CVD diamond coatings possess excellent tribological properties. This material offers the potential to enhance mechanical seal performance in terms of reduced wear and friction and increased reliability and life.

Polycrystalline diamond coatings have, therefore, been deposited by microwave plasma-assisted CVD onto various grades of silicon carbide. The coating morphologies and substrate properties were varied systematically using the Taguchi Method. A Taguchi array has been carried out in which the performance of the coatings was assessed against a range of counterface materials in a thrust washer test rig. The results of these tess are reported here. Consideration is also given to the role of microasperities in determining the performance of a seal.

This work was carried out under a project funded under the DTI EPSRC LINK Surface Enigeering Programme.

The deposition of hard coatings with CVD-processes is commonly used to improve the wear resistance e.g. of tool steels in forming. The advantages of CVD are undisputed (high deposition rates with simple equipment, excellent coating properties). Nevertheless, the disadvantage of the CVD-process is the high deposition temperature, consequently the properties of steel substrates are negatively influenced. Therefore, a subsequent heat treatment of the coated steels is necessary to restore the properties of steels ready for operation.

Induction surface hardening is used as a method of heat treatment after the deposition of TiN hard coatings on steel substrates. Influences of both the coating properties and the substrate properties are discussed in dependence on the parameters of induction heating. Thereby the heating time, heating atmosphere and the power input into the specimen are changed.

The effect of induction surface hardening on the properties of the coating-substrate-systems is mainly characterized using investigations of microstructure and chemical composition as well as measurements of hardness and residual stresses in dependence on the distance from the surface. Furthermore, the scratch test is used to estimate critical loads for cohesive and adhesive failure of the coatings. Additionally, distortion measurements are carried out.

The results emphasize the advantage of induction surface hardening as a method of subsequent heat treatment of CVD-coated steels.

Nowadays mechanical systems operate in increasingly severe conditions, such as intensive loads, high speeds and harsh environments. Therefore designers are continually stretching the limits of the existing materials. To extend the use of available materials beyond their conventional limits' manufacturers are turning to different surface treatments and to hard protective coatings. The main limitation to more extended use of hard ceramic coatings is the load bearing capacity of the coating-substrate system. Due to very thin nature of the hard ceramic coatings, the substrate must bear the majority of the applied load. If the substrate has insufficient strength to bear the contact loading and thus support the coating, plastic deformation will occur, leading to premature failure of the coating. The challenge to improve the properties of hard ceramic coatings by thermochemical pre-treatment of the substrate has gained much attention in recent years leading to a new method called duplex treatment. Duplex treatment is an interesting method not only for increasing load bearing capacity but also for improving fatigue strength, temperature resistance and wear behaviour of mechanical components, particularly under high loads.

In our study samples made of AISI 4140 steel pre-treated by plasma nitriding and coated by two different PVD coatings (TiN and TiAlN) were investigated with respect to the microhardness, surface roughness, residual stress, scratch adhesion and the dry sliding wear resistance. Wear tests in which duplex treated pins were mated to hardened ball bearing steel discs were performed on pin-on-disc machine. To examine the influence of nitrided zone on the performance of coating-substrate composite coatings were deposited on hardened as well as on plasma and pulse plasma nitrided samples nitrided under two different nitriding conditions; in conventional 25%N₂ and in N₂ poor gas mixture.