Positron lifetime study of the single-phase B2Ni(100-x)Al(x) and Ni50-xCOxAl50 intermetallics

In order to understand the point defect structure in NiAl Intermetallic com pound, 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. I t is shown that the positron lifetime spectra of these compounds can be con sistently expressed by single-component lifetimes. The positron lifetime va lue in ternary Ni50-xCoxAl50 alloy is independent of Co content and equal t o that detected in both stoichiometric and Al-rich NiAl. From an analysis o f the present results, it is suggested that the constant lifetime of tau ap proximate to 180 ps should be ascribed to saturation trapping and annihilat ion of positron exclusively at Ni vacancy, no evidence for the presence of Al vacancy is available.