Tribological behaviour of oriented diamond coating/steel couples under various environments

With its remarkable physical properties, diamond is expected to have many applications in industrial and engineering fields. A high hardness combined with a low wear rate are two of the numerous advantages which make it suitable for machining. This makes it necessary to understand its tribological properties. From studies dealing with the frictional behaviour of diamond it has been seen that the deposition method as well as the deposition parameters have a great influence on the coating properties; in particular, a modification of these parameters induces a change in the crystals' growth direction. This paper presents results concerning the tribological behaviour of {111}, {110} and {100} oriented diamond coatings, obtained by flame process, sliding against steel under different environments (vacuum, oxygen, water vapour). It was proved that crystal orientation as well as the environment influence the friction process: transfer nature; disc sliding tracks; coating sights; and friction coefficients are significantly modified. The importance of the normal load was also highlighted, especially under water vapour where an artificial increase in the friction coefficient appears. Scanning electron microscopy observations were also carried out to show surfaces changes. Raman spectrometry and electron diffraction spectroscopy analyses were done to confirm and explain the observed phenomena from the experimental results.