Site occupancy preferences in the B2 ordered phase in Nb–rich Nb–Ti–Al alloys

The β-(Nb, Ti) solid solution phase in the Nb–Ti–Al system has recently been observed to extend to Al concentrations as high as 40 at.%. Five alloys with compositions (in at.%) of Nb–xTi–15Al, where x=17, 28.3 and 34, Nb–25Ti–25Al and Nb–24Ti–40Al were investigated. The β-transus temperatures, lattice parameters and β → B2 (βo) ordering temperatures are reported. Site occupancy preferences of the B2 lattice as a function of alloy composition were examined through the atom location by channeling enhanced microanalysis (ALCHEMI) technique with results presented as ordering tie lines. Ti substitution for Nb on Nb sublattice sites was observed in all of the alloys, with the strength of partitioning between Ti and Al atoms being dependent on alloy composition. A correlation between the partitioning behaviors of the atomic species and the Nb:Ti ratio of the alloy compositions was observed, along with changes in the lattice parameters and microhardness.