A STUDY OF THE INITIAL-STAGES OF DIAMOND DEPOSITION ON FERROUS SUBSTRATES COATED BY A NITRIDED CHROMIUM INTERLAYER AND ON NITRIDED POLYCRYSTALLINE CHROMIUM SUBSTRATES

The use of a nitrided chromium interlayer has been found to improve th e interfacial properties of diamond films deposited on ferrous substra tes. This is achieved by hindering diffusion processes of carbon and i ron, good adhesion of the interlayer to the steel substrate, and very stable mechanical and chemical bonding between the interlayer and the diamond film. In the present study the initial stages of diamond depos ition on steel substrates coated by a nitrided chromium interlayer and on nitrided polycrystalline chromium substrates are reported. Nitrida tion of chromium films deposited by electrochemical methods and polycr ystalline chromium substrates resulted in the formation of two chromiu m nitrides phases, CrN and Cr2N, and a rough surface morphology. The i nitial stages of diamond deposition were found to be accompanied by ca rburization of the substrates surface resulting in chromium carbide fo rmation. The incubation time, diamond particle density and growth rate at the very initial stages of the deposition process were found to di ffer for these two substrates. It is suggested that these differences originate from different carburization rates of the two substrates. Ph ase transformation, recrystallization and diffusion processes in the n ear surface regions of both substrates resulted in very stable chemica l bonding and good adhesion of the diamond film to the substrates. Ram an spectra of the deposited films, on both substrates, show shift of t he diamond peak position to higher wave numbers and split of the peak. These effects are associated with compressive stresses in the diamond film. Residual stresses in the deposited films were calculated from t he shift of the diamond Raman peak. The residual stresses, as calculat ed from the Raman spectra, were found to increase with deposition time reaching values of 5.4 and 6.9 GPa for continuous diamond films on st eel substrate coated with the nitrided chromium film and on nitrided c hromium substrates, respectively. Based on a simple model it was estim ated that thermal stress, arising from mismatch between the thermal ex pansion coefficient of diamond and the underlying substrate, is the ma jor component of the compressive stress in the diamond films. (C) 1997 Elsevier Science S.A.