Nitrogen-Induced Nanocrystallinity of CVD Diamond Films on Ti-6Al-4V Alloys

Microwave plasma chemical vapor deposition (CVD) was used to grow nanocrystalline diamond films by adding nitrogen to a high density plasma defined by a high operating pressure (125 Torr) and high methane feedgas concentration (15% in a balance of hydrogen). Films grown at these conditions but without nitrogen exhibited well-faceted, high phase purity crystalline diamond while those grown with added nitrogen showed a nanocrystalline structure and were an order of magnitude smoother. The nitrogen-induced nanocrystalline films are believed to be comprised predominantly of diamond nanocrystallites in a matrix of tetrahedral amorphous carbon. The films were characterized by Raman spectroscopy, grazing-angle x-ray diffraction, surface profilometry, nano-indentation, electron microscopy, and pin-on-disc tribometry. In contrast to standard CVD conditions, the high density plasma results in adhered films on Ti-6AI-4V substrates even at substrate temperatures of 850°C. We present plasma optical emission spectroscopy results which are correlated with changes in the Raman spectra and the film microstructure. The hardness of the films (∼90 GPa), their low rms surface roughness (27 nm), and their good adhesion to the substrate makes these films potentially useful for tribological applications.