Determination of vacancy concentration and defect structure in the B2 type NiAl β-phase alloys

Abstract

The B2 type NiAl {beta}-phase alloys exhibit a complex type of point defects as the constitutional defect in off-stoichiometric composition regions. This was first established by Bradley and Taylor from the measurements of density and lattice constant. Their proposed defect structure model, the BT model, is that, on the Ni-rich side of stoichiometry the Ni antistructure defects, the Ni-ASD, resulting from substitution of the excess of Ni atoms on the Al-site which is the lattice site assigned to Al atoms, are formed, whereas instead of formation of the Al-ASD, the vacancies on the Ni-site, the Ni-vacancies, are created on the Al-rich side. In this paper which is concerned with the defect structure appearing in the NiAl {beta}-phase, the authors report the results of density measurements by the use of powdered samples instead of bulk material and the results of X-ray analyses performed for these samples based on their own density data.