A new regime is reported for synthesis of nanostructured diamond films on Ti-6Al-4V alloy and molybdenum substrates using microwave plasma chemical vapor deposition (CVD) at high pressure (125 Torr) and high methane feed-gas concentration (5%-15% in a balance of hydrogen). These films are shown to be predominantly comprised of diamond nanocrystallites in a matrix of tetrahedral amorphous carbon. Io contrast to standard CVD conditions, the high density plasma results in adhered films on the metal substrates even at substrate temperatures of 850°C. These films are also significantly smoother than conventionally processed CVD diamond films and have a rms surfaces roughness of about 50 nm. The average grain size of these nanocrystalline diamond films is 13 nm as determined from x-ray diffraction data and the hardness of the films as determined from nanoindentation data is 90% that of natural diamond. Micro-Raman studies using 458 and 647.1 nm excitation indicate an increasing tetrahedral amorphous carbon content with increasing methane feed-gas concentration. The adhesion and mechanical properties of these films makes them attractive for a variety of tribological applications. © 1998 American Institute of Physics.