J. Phys. IV France 05 (1995) C8-91-C8-99
X-Ray Diffraction Study of Thermally and Stress-Induced Phase Transformations in Single Crystalline Ni-Mn-Ga AlloysV.V. Martynov1, 2
1 Institute of Physics of Metals National Academy of Sciences of Ukraine, Kiev, Ukraine
2 Ti-Ni Alloy Company, 1621 Neptune drive, San Leandro, CA 94577, U.S.A.
Using in-situ single crystal X-ray diffraction methods, thermally- and stress-induced crystal structure evolution was investigated in two Ni-Mn-Ga Heusler-type alloys. For the 51at.%Ni-24at.%Mn-25at.%Ga alloy it was found that application of external stress in a temperature range ~20 °C above the Ms at first causes intensity changes of X-ray diffuse scattering peaks in β-phase. Further stressing results in stress-induced phase transformations and under the appropriate conditions three successive martensitic transformations (one is parent-to-martensite and two are martensite-to-martensite transformations) can be stress induced. Of these only the parent-to-martensite transformation can be thermally-induced. Two successive structural transformations (thermally-induced parent-to-martensite and stress-induced martensite-to-martensite transformations) were found in 52at.%Ni-25at.%Mn-23at.%Ga alloy. Crystal structure, lattice parameters, type of modulation, and the length of modulation period for all martensites were identified
© EDP Sciences 1995