Surface and interface characterization of diamond coatings deposited on pure titanium

Diamond coatings appear to be a promising solution for the improvement of tribological behavior of titanium alloys. By means of microwave plasma assisted chemical vapor deposition (MW-PACVD), diamond coating has been deposited on pure titanium substrates using CH4/H-2 mixtures at moderate temperature (550-600 degrees C). The surface and interface characterization of deposition coating with increasing deposition duration up to 21 h has been studied using SEM and grazing incidence X-ray diffraction (GIXD). TiC formation on the substrate surface was detected after 15 min deposition. Growth of TiC competed with diamond formation for the available carbon. The formation of a thick porous TiC layer appeared to promote interfacial debonding and spallation of the diamond coating. During the deposition of diamond coatings, hydrogen diffused into Ti substrate, and the formation of titanium hydride was detected by GIXD. The formation of TiC and diamond layers did not inhibit the formation of titanium hydride. This led to profound microstructural changes and a severe loss of impact strength. A two-step process with higher ratio of CH4 during the first step deposition appeared to be beneficial as a result of the higher nuclei density of diamond crystals. The diamond coating so formed was observed to be in more intimate contact with the substrate. (C) 1999 Elsevier Science S.A. All rights reserved.