Calculation of isothermal sections of three ternary Ti-Zr-X systems

The equilibrium phase diagram of the binary system Ti-Zr shows complete solubility in both allotropic forms, the high temperature β-phase (bcc structure) and the low temperature α-phase (hexagonal structure). In the present paper the influence of additions of a third element (X = Hf, Nb, Ta) on the relative stability of both phases has been analyzed. Hf does also exhibit the two allotropic forms, and both show complete solubility for Zr and Ti. The other two elements crystallize as bcc. Nb is completely soluble in β-Ti, but only at higher temperatures in β-Zr. Its solubility in the α-Ti and α-Zr phases is very limited. Ta is also completely soluble in β-Ti but shows only limited solubility in β-Zr, α-Zr and α-Ti. Calculated isothermal sections of these three ternary equilibrium phase diagrams as well as considerations concerning thermodynamic parameters are presented and discussed in this work