With its excellent mechanical and chemical properties (low wear rate, hardness, chemical inertness), diamond coatings asserted themselves in many industrial applications, and more particularly in the cutting tools field.

Most of the used diamond coatings are obtained by Chemical Vapour Deposition (CVD) assisted by plasma and RF, but their low growth rate (1µm/h) remained a major disadvantage ; it was therefore necessary to find a more efficient process. In spite of some drawbacks, the combustion flame process became then attractive because it offers a high growth rate and can easily be realised.

The tribological behaviour of the thus obtained diamond coatings shows significant differences compared with the properties of other diamond coatings ; these variations depend on the elaboration conditions and processes, on the crystallographic structures and on the environment.

The aim of this paper is to highlight some parameters from which originated these differences. The crystals orientation, the surface reactivity linked to the presence of dangling bonds, the nature of the counterface are some of theses factors influencing the tribological behaviour.

The friction coefficient evolution, versus the time, depends on the gases quantities present in the lattice, and on the ability of this latest to release these gases.

The transferred layer from the counterface to the diamond coating, whom sight depends on the roughness of this one, can play the role of a protective film, and can improve the coating lifetime in the case of cutting tools applications.

The morphology and composition modifications of both the diamond coating and the counterface are highlighted by Scanning Electron Microscopy observations and Energy Diffraction Spectroscopy and Raman Spectroscopy analyses.

In the present high-density magnetic recording technology, the protective film thickness of magnetic heads has been reduced to below 10 nm. For such ultrathin films, improvement of inherent wear durability and adhesion characteristics of the films are critical in determining the film design and its tribological performance. Furthermore, to realize such ultrathin protective films, an evaluation method which can evaluate independently their inherent wear durability and adhesion characteristics is needed. We proposed the such an evaluation method for ultrathin films using an AFM nanowear test ¹.

By applying the proposed method, we clarified the deposition conditions for the highly wear-durable carbon films prepared by electron-cyclotron-resonance (ECR) plasma sputtering. The wear durability of the ECR-sputtered films was far superior to that of the RF-sputtered films. ECR-sputtered films made with high energy ion irradiation showed the highest wear resistance, nearly comparable with that of bulk diamond ². We attribute this high durability to selective etching of the weakly bonded carbon atoms by the high-energy ion irradiation. Furthermore, we also clarified the most suitable deposition conditions of an adhesion layer for the ECR-sputtered carbon films by applying the proposed method.

Therefore, the highly wear-durable ECR-sputtered carbon films and the proposed method will have important roles in the head-media interface design for the next generation of high-density magnetic recording technology.

¹ S. Umemura, et al, IEICE Trans. on Electronics, E81-C, 337 (1998).
² S. Hirono, et al. IEEE Trans. Mag., 34, 1729 (1998).

A high hardness and a low wear rate combined to exceptional physical properties make diamond an ideal candidate for machining. It is particularly interesting for tooling aluminium and its alloys as it offers these soft materials a clean cutting and lets the shaving sliding on the tool surface.

It results from studies dealing with the diamond / aluminium friction that the tribological behaviour of this couple is greatly influenced by the presence of oxides, more particularly Al₂O₃, on the counterface surface. It was then necessary to better understand the role of these oxides during the cutting process, the way they modify the nature of the contact, their effects on the transferred layer formation. paragraph The tribological behaviour of diamond coatings obtained by combustion flame process, sliding against aluminium or aluminium alloys under different environments (vacuum, oxygen and water vapour) with a varying applied normal load is presented here ; the modifications of both the coating and the counterface, the friction coefficient evolution and the transferred layers are especially studied.

The surfaces changes are revealed by Scanning Electron Microscopy observations. Raman spectroscopy and Energy Dispersive Spectroscopy analyses were realised to highlight the observed phenomena.