Neutron diffraction study of the structure and low-temperature phase transformation in ternary NiAl + M (M = Ni, Fe, Co) alloys

Neutron diffraction was used to study the structure of ternary NiAl + M (M = Ni, Fe, Co) alloys. The experiment confirmed the predictions by first-principle calculations on site preference by solute atoms. Moreover, a universal structural transformation was observed below 20 K in alloys where Al is partially replaced by M. The extra peaks at low-temperatures do not match those from known martensite phases, but are well indexed by a cubic structure. A possible mechanism for the low-temperature phase is discussed.