Internal defects of B19' martensite via R-phase in Ti-Ni-Fe and thermally cycled Ti-Ni alloys

Crystallography and morphology of B19' martensite via R phase transformation in Ti-Ni-Fe alloy have been investigated by X-ray diffraction and transmission electron microscopy. The microstructure aspects of the B19' martensite in the solution treated Ti-Ni-Fe alloy was the same as those in the solution treated binary Ti-Ni alloy. In the thermal cycled Ti-Ni-Fe alloy, the (001)_b19' compound twins frequently observed were the same as those in the thermal cycled binary Ti-Ni alloy. It is considered that the (001) _b19' compound twin was a kind of deformation twin to reduce the internal stress due to dislocations introduced during the thermal cycle, rather than a lattice invariant shear of the R to B19' transformation.