One-step CVD-diamond coating process on 3-D titanium substrates using reticulated vitreous carbon as a solid carbon source N.A. Braga a, ⁎, C.A.A. Cairo b , N.G. Ferreira a , M.R. Baldan a , V.J. Trava-Airoldi a a Instituto Nacional de Pesquisas Espaciais, INPE, 12245-970, São José dos Campos, SP, Brazil b Comando-Geral de Tecnologia Aeroespacial, CTA, 12228-904, São José dos Campos, SP, Brazil abstract article info Available online 6 February 2010 Keywords: Nanocrystalline diamond 3D porous titanium RVC Eletrochemical Nanocrystalline diamond (NCD), formed on three-dimensional (3D) titanium (Ti) substrates, through the etching of reticulated vitreous carbon (RVC) was investigated. Porous Ti was prepared by powder metallurgy and the RVC was produced at 1300 and 2000 °C graphitization index. In this chemical vapor infiltration/ deposition process, the RVC sample was used as the only carbon source that ensured the production of pertinent growth species directly on the Ti surfaces including its inner and bottom (the opposite side of the sample). The films were deposited at 630 °C substrate temperature. NCD scanning electron microscopy images showed agglomerates of nanometer crystallites with a uniform surface texture covering all sample. Raman measurements showed the typical two shoulders at 1150 and 1490 cm -1 attributed to NCD formation. Electrochemical response by cyclic voltammetry measurements confirmed a wide potential window for such electrodes in addition to its exceptional reversibility response. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Nanocrystalline diamond (NCD) films emerge as a technological potential material owing to their unique properties. The major applications include microelectromechanical systems, electron-field emitters, tribological, semiconductors, electrochemistry and bioma- terial [1–3]. As diamond, titanium (Ti) properties make it appropriate for industrial, aerospace and biological applications [4,5]. Despite its excellent properties, it is well known that Ti presents low resistance under cyclic strain conditions. However, coating with hard materials like NCD films can transform its wear-resistant and increase its applications. The diamond deposition on Ti substrates with high and interconnected porosity, called three-dimensional (3-D) porosity, appears as a novel area. Such substrates may be obtained by powder metallurgy process by varying the porosity level and pore size and shape [6]. There are few works in the literature investigating diamond films deposited under this kind of substrate [7,8]. Conventional CVD growth process allows obtaining synthetic diamond from a gaseous carbon source, such as methane diluted in a high concentration of the gaseous hydrogen [9]. The gas mixture generates carbon radicals in a large flux of atomic hydrogen which is believed to play a central role in the diamond CVD process [9,10]. The kinetic modelling of the hot filament chemical vapor deposition (HFCVD) of NCD on Ti–6Al–4V substrates has been investigated by Jackson et al. [11]. They showed that the gas phase chemistry was altered from C1 to C2 growth species using Ar concentrations higher than 70 vol.%. At these concentrations, the C2 dimmer dominated the gas phase chemistry. More recently, from experimental and modelling results, May and Ashfold [12] raised a new point of view. According to them, the ultrananocrystalline diamond (UNCD) growth mechanism is dominated by a balance between the CH 3 and C2 (and/or C 2 H) radical concentrations close to the substrate surface during the UN/ NCD growth. This balance determines the growth morphology and film properties. The studies described above indicate the importance of further information about the carbon species role in the gas mixture for NCD growth, as well as, about its effect on NCD morphology and properties. Besides, there are no reports exploring the growth of NCD films on Ti substrates by using only a solid carbon source as an infiltration process into deep 3D-Ti substrate. For this propose reticulated vitreous carbon (RVC) treated at two different temperatures of 1300 and 2000 °C was used. After carbonization process, RVC presents a disordered porous glassy carbon (GC) structure with some crystallo- graphic order associated with its graphitization index. From RVC1300, the major contribution comes from the high oxygen content presented. The oxygen presence in the gas phase for diamond growth has already extensively studied [13] and has shown that the OH formation is more efficient for etching sp 2 and sp 3 bonds than atomic hydrogen itself. Also, the oxygen presence favours the CO formation from carbon excess provided by substrate etching. These contribu- tions decreased the film growth rate and favour the highest substrate etching. For RVC2000 the surface bond does not present oxygen content, but presents a structure closer to graphite arrangement that may facilitates the attack on graphitic structures and are more Diamond & Related Materials 19 (2010) 764–767 ⁎ Corresponding author. Fax: + 55 12 39456717. E-mail address: neila@las.inpe.br (N.A. Braga). 0925-9635/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2010.01.041 Contents lists available at ScienceDirect Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond