High-temperature phase equilibria in the Al-rich corner of the Al-Ti-C system

A thermodynamic analysis of the Al-rich corner in the ternary Al-Ti-C diagram, providing phase relations and regions of phase stability, is presented. An invariant four-phase equilibrium between Al, Al₄C₃, Al₃Ti, and TiC_x takes place at 0.53 at. pct Ti, 7.10^-6 at. pct C, and TiC_0.883 at 966 K. The carbon content of the TiC_x phase, which extends from x = 0.48 to 0.98, exerts a significant effect on phase relationships in this ternary system. In particular, it is shown that stoichiometric TiC is not stable in the presence of liquid Al. For example, at 1300 K, a two-phase equilibrium between Al_L and TiC_x exists only in the 0.91 < x < 0.82 range. Thus, the interaction of Al_L with stoichiometric TiC leads to the formation of the Al₄C₃ aluminum carbide phase, whereas for x < 0.82, only the intermetallic compound Al₃Ti can form at this temperature. The results of this analysis were confirmed by X-ray diffraction (XRD) measurements of relevant composites.