Effect of chromium on the kinetics of the contact melting and the graphite-to-diamond transformation in the Co-Fe-C system

We have studied the effect of chromium concentration in alloys of the Co-Fe system on their interaction with graphite at p, T parameters of thermodyna mic stability of diamond. It has been found that addition of chromium to th e alloys stabilizes the Me3C-type carbide, as a result, the structure of a layer of a contact melting at the alloy-graphite interface is identical to a horizontal section of the metastable phase diagram of the Fe-C system. It is shown that addition of chromium to the Co-Fe-C system lowers the eutect ic melting temperature by 80-100 K In this case, the coefficient of carbon diffusion in the melt increases by similar to 20-30%. An increased surface activity of a Cr-containing melt with respect to graphite is noted, which i s the reason of intensive intrusion of the melt deep into a graphite layer along the grain boundaries. As a result, the number of nucleating diamond c rystals and the degree of the graphite --> diamond transformation increases . (C) 2001 Elsevier Science B.V. All rights reserved.