Discussion of "On the free energy of formation of TiC and Al₄C₃"

Several years ago, Banerji and Reif^[1] 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 1000 °C 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 1175 °C, with A1₄C₃ having the lower free energy of formation below this temperature. There are several aspects of this work which merit further discussion.