Advanced transmission electron microscopy study on premartensitic state of Ti50Ni48Fe2

Microstructure of the premartensitic state in Ti50Ni48Fe2 is extensively analyzed by advanced transmission electron microscopy utilizing energy filtering and in situ dark-field imaging. From the energy-filtered electron diffraction study, microdomains less than 5 nm with transverse atomic displacement are clarified to extend preferably in the 110 directions. Careful energy-filtered dark-field electron microscopy reveals that each microdomain has a single transverse type of atomic displacement whose propagation and displacement directions are such as the [011] and [01] directions, respectively. Furthermore, from in situ dark-field electron microscopy, the growth process of the microdomains is observed dynamically for the first time. Size limitation of the microdomains is discussed in terms of the lattice strain without the translational symmetry accompanying the transverse atomic displacement.