The annealing of vacancies in Ni52Al48 at 635 to 685K was studied, over a 1-year time-scale, by positron annihilation spectroscopy. The positron lifetime of 179ps in as-prepared material revealed the presence of remnant single vacancies. A decrease in the concentration of these vacancies, with annealing time, demonstrated that they could be removed by low-temperature long-term annealing; leading to vacancy clusters. A vacancy migration enthalpy of 2.0eV was deduced from the annealing data. The remnant single vacancies were suggested to be located on the Ni sub-lattice of ordered NiAl.

Slow Removal of Vacancies in B2-Ni52Al48 upon Long-Term Low-Temperature Annealing. X.Y.Zhang, W.Sprengel, K.J.Reichle, K.Blaurock, R.Henes, H.E.Schaefer: Physical Review B, 2003, 68[22], 224102 (4pp)