MARTENSITIC-TRANSFORMATION IN NITI INVESTIGATED BY SYNCHROTRON X-RAY-DIFFRACTION

Thermoelastic martensitic transformation of equiatomic NiTi has been i nvestigated by synchrotron X-ray diffraction. The SR-source VEPP-3 was used to obtain X-ray patterns in a wide range of diffraction angles s imultaneously, while heating or cooling. Diffraction angle resolution of the parallel single-coordinate detector was 0.008 degrees, and the wavelength was 0.14879 nm. At the same time the parameters of the B2, R, B19' phases have been determined and compared with literature data. We observed both reversible changes of the parameters b and c of the unit cell of B19'-martensite, evolution of the doublet reflex (202) an d ((2) over bar 02) of the R-phase, and volume effects under transform ation. It has been demonstrated, that martensite preferably appeared i n the more loose lattice rather than in an equilibrium state.