It was noted that the lifetime spectra of NiAl and NiCoAl samples could be described by a single-component constant of 166.7 to 182.1. In the case of the binary alloy, the further the Al content was away from stoichiometry on the Ni-rich side, the shorter was the positron lifetime. However, the positron lifetime remained constant as the Al content increased away from stoichiometry on the Al-rich side. In the case of the ternary alloy, the positron lifetime was independent of the Co content and was equal to that observed in stoichiometric and Al-rich NiAl. It was suggested that the observed lifetime (180ps) in stoichiometric or Al-rich NiAl, and NiCoAl, could be attributed to the saturation trapping and annihilation of positrons at Ni vacancies.

A Study of Vacancy-Like Defects in Single-Phase NiAl by Positron Annihilation. R.S.Chen, J.T.Guo, W.L.Zhou, L.Y.Xiong: Scripta Materialia, 2001, 43[9], 789–94