Concentration of point defects and site occupancy behavior in ternary NiAl alloys

A model was established under the mean-field first nearest neighbor interaction approximation to evaluate the concentration of point defects and the site occupancy of micro alloyed NiAl. The theoretical results suggest that micro alloying has only slight effect on point defect formation. The vacancy concentration decreases in both the Al-rich and the Ni-rich alloys as compared to binary alloys, while the concentration of the Al anti-site defects increases and that of the Ni anti-site defects decreases by about half the difference of vacancy concentration between the binary and ternary systems on the Al- and Ni-rich sides, respectively. At low concentration, Ga, Si, Ge, Ti, V, Zr, Nb, Hf and Ta occupy the Al sublattice, whereas Mn, Fe and Co occupy the Ni sublattice; the dependence of occupancy on composition and temperature is weak. By contrast, the site preference of Mo, W and Cr changes considerably with alloy chemistry and temperature and they show strong tendency to occupy both sublattices at high temperature. In general, with increasing atomic number, transition metal elements in the same period increasingly tend to substitute for Ni.