Threshold Displacement and Interstitial-Atom Formation Energies in Ni₃Al

Threshold displacement energies for atomic displacements along 〈110〉, 〈100〉, and〈111〉 directions, and formation enthalpies of several symmetric interstitial atom configurations were calculated for Ni₃Al by computer simulation using 'embedded atom method' potentials. The Ni-Ni (100) dumbbell in the plane containing only Ni atoms has the lowest interstitial-atom enthalpy although the enthalpies of other configurations are similar. Interstitial configurations involving Al atoms all have much higher enthalpies. The anisotropy of the threshold energies in Ni₃Al is similar to pure metals and no significant difference in threshold energy was observed for 〈110〉 replacement chains in rows containing all Ni atoms or alternating Ni-Al atoms. Various metastable interstitial atom configurations were observed, including crowd-ions. In addition, the spontaneous recombination volume for some configurations can be much smaller than in pure metals. The consequences of these results for radiation induced segregation and amorphization are discussed.