Low temperature x-ray diffractometry of the shape memory Fe-Ni based alloys

By means of x-ray diffractometry the structure of martensite in carbon-free ferrous alloys possessing shape memory has been studied. A low temperature device was used for the registration of diffractograms for temperatures which were lower than the start martensitic transformation temperature. The value of the martensite crystal lattice tetragonality and its dependence on alloy composition were determined. A correlation between the martensite tetragonality and the thermal hysteresis of the martensitic transformation was noted. A high tetragonality of martensite, c/a approx1.19, was found. The relationship of the transformation thermal hysteresis and the degree of coherent strain relaxation on the interfaces was analysed.