A study of vacancy-like defects in the single-phase NiAl by positron annihilation

The lifetime spectrum of the binary NiAl and ternary NiCoAl samples was expressed by single-component lifetime constant of τ=166.7-182.1 with a maximum error less than 0.6ps. In the binary Ni100-xAlx, the further the Al content was away from the stoichiometry on the Ni-rich side, the lower was the positron lifetime, whereas the positron lifetime remained unchanged as the Al content increased from the stoichiometry to the Al-rich side. In the ternary Ni50-xCoxAl50 alloy, the positron lifetime was independent of Co content and equal to that observed in stoichiometric and Al-rich NiAl.