The site occupation of
alloying elements on various sublattices of intermetallic compounds directly
affects their properties. The precipitation of the α2 phase (Ti3Al intermetallic compound)
serves as a key strengthening mechanism in high-temperature titanium alloys.
However, due to the complex composition of these alloys and the nanoscale size
of the α2-Ti3Al
phase, the occupation behavior of alloying elements in α2-Ti3Al remains unclear. Theoretically, this
behavior can be predicted by calculating the formation energies of alloying
atoms on different sublattices, which requires knowledge of the chemical potentials
of the matrix atoms (Ti and Al in Ti3Al) as reference energies.
Conventionally, these chemical potentials are approximated by the energies of
the elements in their standard states. However, this approach is inadequate for
determining site occupations in α2-Ti3Al
precipitated in high-temperature alloys, as it neglects the phase equilibrium
between the precipitate and matrix, which governs the chemical potentials. In
addition, the influence of temperature on site occupation in α2-Ti3Al has not
yet been theoretically addressed. In this study, the chemical potentials of Ti
and Al are evaluated based on the phase equilibrium between the α-Ti matrix and the α2-Ti3Al precipitate. The formation energies
of alloying elements on Ti and Al sublattices are then computed using
first-principles methods, and their site preference is assessed by comparing
these formation energies. Furthermore, the temperature-dependent partitioning
of alloying elements between the two sublattices is determined based on site
preference energy. The results show that, at service temperatures of
high-temperature titanium alloys, elements such as Sc, V, Cr, Mn, Fe, Y, Zr,
Nb, Mo, Tc, Ru, Hf, Ta, W, Re, and Os preferentially occupy the Ti sublattice;
Si, Ni, Cu, Zn, Ga, Ge, Ag, Cd, In, Sn, Pt, Au, Hg, Tl, and Pb preferentially
occupy the Al sublattice; while Co, Rh, Pd, and Ir distribute over both
sublattices.
