Changes in microstructure near the R-phase transformation in Ti50Ni48Fe2 studied by in-situ electron microscopy

Microstructural changes associated with the martensitic transformation from cubic (parent phase) to trigonal (R phase) which occurs with decreasing temperature in Ti50Ni48Fe2 have been intensively studied by in-situ electron microscopy. Although the parent phase shows a characteristic microstructure with small domains, which are due to lattice modulation as a precursor to the transformation, their temperature dependence is contrasted with that of domains which appear below the transformation temperature in the R phase. The observations convince us that there is an essential difference between the natures of the domains observed in each state, and also reveal the formation of peculiar antiphase-like boundaries within a needle-like variant of the R phase. We also estimate the approximate size of the R phase just after nucleation and compare this with a theoretical consideration on the size of nuclei in martensites.