INTERACTIONS BETWEEN LIQUID NICKEL AND VITREOUS CARBON

The behaviour of liquid nickel in contact with vitreous carbon and graphite has been investigated. At a temperature of 1743 K, vitreous carbon is attacked by pure nickel more strongly than graphite, i.e. the metal penetrates the substrate more deeply, and, after cooling, a nickel matrix containing a larger amount of graphite (which has precipitated) can be observed. Considerations about the depth of penetration of the metal into the substrate and about the microstructures of the two systems after cooling lead to the hypothesis of a carbon supersaturation of nickel in the presence of vitreous carbon. However, vitreous carbon, like the graphite substrate, is not attacked by nickel previously saturated with carbon. In this case, the melt does not penetrate and, after cooling, its microstructure is analogous to that of the pure nickel-graphite system. Near the eutectic temperature (1618 K), vitreous carbon is attacked by pure nickel according to the nickel-graphite phase diagram. The mechanism accounting for the observed behaviours may be possible formation of the metastable Ni3C carbide at 1743 K.