Determination of site occupation probability of Cu in Ni₃Al by atom-probe field ion microscopy

The site preference of Cu in Ni₃Al with a composition of Ni₇₅Al₂₃Cu₂ has been determined by atom-probe field ion microscopy (APFIM). The sample was analyzed in the three major low index planes with atomic layer resolution. From the data chain obtained in the [001] direction the site occupancy of Cu atoms was determined by analyzing whether they were evaporated from the NiAl mixed planes or the Ni pure planes. It has been determined from an extensive number of quantitative data that the fraction of the Cu atoms in the Ni sites of the Ni₇₅Al₂₃Cu₂ intermetallic compound is 94_-10⁺⁶%. The present finding substantiates the recently proposed mechanism which explain the ductilization of Ni₃Al by adding a few atomic percent of transition elements, such as Pd and Cu.