From micro to nanocrystalline transition in the diamond formation on porous pure titanium

A novel composite material of nanocrystalline (NCD) and/or microcrystalline (MCD) diamond films grown on porous titanium (Ti) substrate was obtained by hot filament chemical vapor deposition technique. Diamond films were grown using 1.5 vol.% CH4 in a balanced mixture of Ar/H-2. The grain size control was obtained by varying the argon concentration from 0 up to 90 vol.% at substrate temperature of 870 K. Porous Ti substrates were obtained by powder metallurgy and presented an inter-connected open porosity. Scanning electron microscopy images of diamond/Ti exposed the substrate covered by a continuous textured coating which changed from MCD to NCD morphology; depending on the amount of Ar concentration in the feed gas. Micro-Raman spectra showed the characteristic t-polyacethylene peaks around 1150 cm(-1) and 1470 cm(-1), associated to NCD formation for samples grown with Ar concentration higher than 40 vol.%. X-ray diffraction patterns identified the diamond and TiC peaks, where the crystallinity of (111) TiC phase decreased as the Ar amount increased. This behavior was associated to diamond (220) peak increase for films grown with Ar concentration higher than 70 vol.%. Diamond crystallite size was also evaluated from Sherrer's formula in the range of 11 up to 20 nm. (C) 2008 Elsevier B.V. All rights reserved.