Evolution of the crystal structure during phase working of titanium nickelide

Using x-ray diffraction we have measured the dynamic and static atomic displacements and the unit cell parameters of monoclinic martensite in the intermetallide 50.1 at. %Ti-Ni, during thermal cycling through the interval of the martensitic transition (280 to 400 K). It is shown that along with a change in the sequence of transitions from B2→B19′ to B2→R→B19′, there is also a change in the atomic displacements from predominantly dynamic on the first cycles to static displacements during the later ones. The martensite unit cell has a larger volume on cooling than on heating, and cycling leads to a lowering of its monoclinic angle.