Martensitic transformation and microstructure in Nb–Ru–Fe shape memory alloys

The martensitic transformation behavior and microstructure in Nb–Ru–Fe alloys have been investigated by means of differential scanning calorimetry, X-ray diffraction, optical microscopy and transmission electron microscopy. It is shown that two-step phase transformation of β → β′ → β″ occurs during cooling from high temperature to room temperature. The monoclinic crystal structure remains unchanged with the addition of Fe, but all lattice parameters of the martensite unit cell decrease with increasing Fe content. The crystal symmetry of martensite is Cmmm. The β″ martensite variants exhibit self-accommodation morphology and the substructure is determined to be (1 0 1) type I twin.