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 [011] 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.