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 TiCx takes place at 0.53 at. pct Ti, 7.10(-6) at, pct C, and TiC0.883 at 966 K. The carbon content of the TiCx 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 TiCx 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.