In this study, the influence of yttrium on the formation of the structural-phase state of the Ti-Al alloy, obtained by the “hydride technology” (GT) method, has been analyzed. Using transmission electron microscopy (TEM) and X-ray spectral microanalysis, the authors of the work have established the following phases formed in the sample volume and on the surface: Ti3Al, TiAl, Al, α-Ti, Ti3Al5, Y2Al, Y5Al3, YAl3, YAl, and Y6Ti4Al43. The lamellar structure has been formed in the alloy volume. The average width of the Al-rich lamellae was 0.36 µm and that of the Ti-rich lamellae was 0.21 µm. The formation of a triple Y6Ti4Al43 phase, which is localized along the boundaries of the lamellar structure, has been recorded. The localization scheme of the formed phases of the TAY alloy has been proposed.

The manuscript describes the phase composition, microstructure, some physical and mechanical properties of the Ti-Al system with addition of 2 at. % Dy (TAD) and Ho (TAH) obtained by “hydride technology”. Phase diagrams for Ti-Al-Dy and Ti-Al-Ho at a temperature of 1150 °С and basic properties for ternary phases Dy6Ti4Al43 and Ho6Ti4Al43 were calculated. A crystallographic database of stable and quasistable structures of the known elemental composition was created in the USPEX-SIESTA software by means of an evolutionary code. The calculations show that adding REM leads to a significant stabilizing effect in each Ti-Al-Me (Me = Dy, Ho) system without exception. It has been established that the lattice energies of AlTi3Ho and AlTi3Dy are, respectively, equal to: EAl4Ti12Dy3 = −32877.825 eV and EAl4Ti12Dy3 = −31227.561 eV. In the synthesized Ti49Al49Ho2 compound, the main phases include Al-Ti, Al3Ti3 and Al4Ti12Ho3 and the contributions to the theoretical intensity are equal to 44.83, 44.43 and 5.55%, respectively. Ti49Al49Dy2 is dominated by the Al-Ti, Al3Ti3 and Al4Ti12Dy phases, whose contributions are equal to 65.04, 16.88 and 11.2%, respectively. The microhardness of TAD and TAN specimens is 1.61 ± 0.08 and 1.47 ± 0.07 GPa, respectively.