In order to understand the point defect structure in NiAl Intermetallic compound, the positron lifetime in binary Ni100-xAlx (53 greater than or equal to x greater than or equal to 45) and ternary B2 Ni50-xCoxAl50 (x=0, 5, 10, 15) intermetallic compounds as a function of composition were measured. It is shown that the positron lifetime spectra of these compounds can be consistently expressed by single-component lifetimes. The positron lifetime value in ternary Ni50-xCoxAl50 alloy is independent of Co content and equal to that detected in both stoichiometric and Al-rich NiAl. From an analysis of the present results, it is suggested that the constant lifetime of tau approximate to 180 ps should be ascribed to saturation trapping and annihilation of positron exclusively at Ni vacancy, no evidence for the presence of Al vacancy is available.
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