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transition at room temperature are taken from Refs. $^{2,3}$. 

On the whole, a good agreement of the calculated triple point ( P$_{theor}$ = 4 . 2 GPa, T$_{theor}$ = 720 K) with the exper- imental values P$_{exp}$ = 4 . 9 ± 0 . 3 GPa, T$_{exp}$ = 733 ± 30 K 1 is observed. At zero pressure the calculated temperature of the β − α transition is T theor β − α = 943 K. This value is higher than the experimental one, T exp β − α = 852 K, defined in Ref. 1 as the average of the temperatures of the tran- sition onset on heating and cooling. It should be noted that a large hysteresis is observed upon the α − β trans- formation in TiZr. At atmospheric pressure the maxima of thermal peaks in the DTA curves fall on T ∼ 912 K on heating and T ∼ 810 K on cooling, the typical peak width being Δ T ∼ 40 K. With this in mind, one can consider the results of calculation of the α − β equilib- rium boundary in the Debye-Gr¨ uneisen model as quite satisfactory. 

The greatest discrepancy between the theoretical cal- culation and the experimental evidence available is ob- served for the α − ω transition. In Ref. 3 the pressure at which this transition occurs at room temperature was estimated to be P exp α − ω = 6 . 6 GPa. Note thet equilib- 

rium point of the α and ω phases was determined under shear-strain conditions at pressures up to 9 GPa. The shearing strain is known to lower the pressure at which the phase transition begins. Presumably for this reason the authors of Ref. 3 failed to obtain the α − ω transition at room temperature under quasi-hydrostatic conditions. In Ref. 2 it was shown by X-ray diffraction method that the α phase of TiZr remains the sole stable phase under quasi-hydrostatic pressure up to 12 . 2 GPa. Only from 5 . 5 GPa on, becomes dominating the ω phase which remains stable up to 56 . 9 GPa. At pressures above 56 . 9 GPa there forms a high-pressure phase with a bcc lattice. 

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As seen from Fig.4, in our calculation at atmospheric pressure and low temperatures the ω phase is stable, there occurs no α − ω transition at room temperature. Note that in our calculations of pure Ti 10 and Zr $^{11}$, in complete agreement with the experimental data, the α phase is stable at atmospheric pressure and room tem- perature, and the ω phase is stable only under pressure. That the ω phase in TiZr at normal conditions is energet- ically preferable, immediately follows from a comparison of the calculated free energies (see Fig.3). Recall that the difference in energy between the α and ω structures in the equiatomic TiZr alloy is almost five times greater than in pure titanium and zirconium. 

The discrepancy between experiment and theory may be due to the fact that the calculation was performed for ideal crystalline structures (see Fig.1),whereas the exper- imental samples were imperfect crystals with lattice de- fects. In particular, it was shown 3 that in a TiZr alloy shear-strained under pressure the ω phase is represented by aggregations of oblong particles with characteristic size of 3 − 5 nm, and 15 − 30 nm long. If ω − phase particles are situated in a coarse grain of α phase, they are mainly located at its boundaries. It was also noted 1 that various imperfect structures in samples pre-treated in different ways have a noticeable effect on the course of structural transformations. Evidently, we could not model a real 

