On the lattice parameters of the B19′ martensite in binary Ti-Ni shape-memory alloys

X-ray diffraction was used to study the concentration, temperature, and deformation dependences of the lattice parameters of the B19'-martensite in Ti-(47.0-50.7 at %) Ni binary alloys. The martensite lattice parameters depend on the nickel concentration in the hyperequiatomic range. The temperature dependences of the martensite lattice parameters are approximately the same for all the alloys studied. The formation of martensite from austenite with a developed dislocation structure in the Ti-50.0 at % Ni alloy and from aged austenite in the Ti-50.7 at % Ni alloy affects the martensite lattice parameters. The variation in the lattice parameters of martensite is not related to a change in the martensite formation scheme from B2 --> B19' to B2 --> R --> B19'. The lattice parameters of martensite are also independent of the strain-induced reorientation of martensite or its plastic deformation to a 25% reduction.