Abstract: The phase transformation behavior and microstructure of Nb-Ru alloys have been stud-ied by DSC, X-ray diffraction, optical microscopy, transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). Two-step phase transfor-mation of CsCl (β) →face-centered tetragonal (β') →, monoclinic (β') occurs during cooling from high temperature to room temperature. The lattice parameters of marten-sites of Nb-Ru alloys were found to increase with the increase of Nb content. The martensite variants exhibit triangular self-accommodating morphology, with alternat-ing regular bands inside. The twinning relationship between the substructural bands was found to be (101) type I mode, and this kind of twinning interface was straight, well-defined and coherent.

Key words: Nb-Ru alloy, shape memorg alloy (SMA), phase transformation,