Positron lifetime spectra have been measured for monodirectional crystal
as-cast polycrystal and hot-rolled polycrystal of Ni-20Al-30Fe alloys.τ2 values for these samples are similar
indicating that lifetime of the positron annihilated in grain boundary is similar to that in a vacancy or a dislocation
and density of free electrons in grain boundaries is nearly equal to that in vacancies.It is concluded that the structure of grain boundaries in NiAl alloy can be improved by alloying with Fe.