The effect of Ti/Al ratio on the site occupancies of alloying elements in γ-TiAl

The site occupancies of V, Cr, Mn, Fe, Ni, Zr, Nb, Ta, Mo, Ga and Sn (1∼5 at%) in TiAl alloys with different nominal Ti/Al ratios were measured by the atom location channelling enhanced microanalysis (ALCHEMI) method. The results showed that Zr, Nb and Ta invariably occupy Ti sublattice sites, whereas Fe, Ni, Ga and Sn occupy Al sublattice sites, the alloy composition having no significant influence on their site preference. By contrast, the site preference of V, Cr, and Mn changes significantly with alloy composition (the Ti/Al ratio in particular), the probability of these elements occupying Ti sites decreasing in the above order. In general, with increasing atomic number, elements in the same period show increasing tendency to substitute for Al, so is the tendency to substitute for Ti for elements in the same group of the periodic table. A discussion is made in terms of the Bragg–Williams model by using published bond order data as input, allowing qualitative interpretation of the experimental findings.