Discussion of "On the Free Energy of Formation of TiC and Al4C3"

Several years ago, Banerji and Reif reported some very interesting studies on a process to react Ti and C in molten Al to form particles of TiC. The process was used to prepare a master alloy with a fine dispersion of TiC to inoculate Al for grain refinement. Approximately 2 wt pct of preheated graphite particles were stirred into the Al-5 to 10 pct Ti melts. The authors explained that the melts needed to be superheated above 1000C to avoid the undesirable formation of A14C3 and Ti3AlC at the TiC/melt interface. Their explanation for this phenomenon was based on thermodynamics. They observed that the standard free energy of formation curves for AI4C3 and TiC cross near 1175C, with A14C3 having the lower free energy of formation below this temperature. There are several aspects of this work which merit further discussion.