Tribological investigation of nanocrystalline diamond films at low load under different tribosystems

The mechanical and frictional properties of hydrogen- and oxygen-terminated nanocrystalline diamond films (NCD) grown by hot-filament chemical vapor deposition (HFCVD) have been investigated in the present work.The structure and morphology of the NCD films have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman-effect spectroscopy. In addition, X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) have been used to investigate the surface chemical groups on the NCD surface. Mechanical and frictional properties are determined using atomic force microscopy (AFM), nano-indentation, nano-scratching and micro-tribometer. The friction behavior of these films in the load range of 25 to 200 mN under reciprocating sliding conditions, using steel counter-body material has been thoroughly studied.It is noted that these films are highly crystalline with nanometer size grains and contain a very high fraction of sp3 carbon bonds. They exhibit high hardness and high elastic modulus. The friction coefficient of the film is lower under unidirectional scratch with diamond indenter than the friction coefficient under low load reciprocating sliding against steel ball. Transfer of the film from the counter-body, oxidation of transfer film and mixing of transfer film with carbonaceous layer on the worn surfaces are responsible for such behavior. Although, the friction responses of H-terminated and O-terminated films are similar under unidirectional scratch with diamond indenter, the friction coefficient of O-terminated film is always higher than the friction coefficient of H-terminated film under reciprocating sliding condition against steel counter-body material.

Research Highlights
► Nanocrystalline diamond films are grown by hot filament chemical vapour deposition technique.
► Films contain nanometer size grains and a high fraction of sp3 carbon bonds.
► Friction behaviour in the range of 25 to 200 mN has been studied under reciprocating sliding condition.
► Friction coefficient of O-terminated film is higher than of H-terminated film.
► Worn surfaces are characterized using, AFM, SEM, XPS and RS.