APFIM investigations on site preferences, superdislocations, and antiphase boundaries in NiAl(Cr) with B2 superlattice structure

The effect of the ternary element chromium in B2 ordered NiAl based alloys was studied by atom probe field ion microscopy. Samples of the compositions Ni50Al48Cr2, Ni49Al49Cr2, and Ni48Al50Cr2 were investigated after different heat treatments. The chromium concentrations of the NiAl matrix, measured by atom probe, increased with increasing Ni/Al ratio and heat treatment temperature. The site preference of solute Cr atoms for the Al sublattice was determined by layer resolved measurements. An antiphase boundary observed in Ni50Al48Cr2 showed a high local Cr concentration with Cr atoms substituting for Al atoms. Superdislocations in the quasi-stoichiometric Ni49Al49Cr2 were not dissociated into partial dislocations and showed no Cr segregation. These results are discussed in view of activation of a〈1 1 1〉 slip systems.