A High Resolution Electron Microscope Study of Martensite and Martensitic Interfaces in Titanium-Manganese

The high resolution two-dimensional lattice fringe imaging technique of transmission electron microscopy has been used to observe a Ti-5% (by mass) Mn alloy, which transforms martensitically from a high temperature body-centred cubic parent phase to a martensite hexagonal close-packed phase. In conjunction with the experimental work, computer simulations of the images have been made by using a program based on the multi-slice approach to the dynamical theory of electron diffraction. The experimental work has produced for the first time two-dimensional lattice fringe images of a parent-martensite interface as well as showing the existence of steps of atomic dimensions, corresponding to twinning dislocations in the internal martensite twin interfaces. These results also suggest an explanation for the fine striated substructure of the martensite. However, the simulations show that the images of the parent-martensite and martensite-twin interface cannot be interpreted in terms of atomic models of these interfaces. The implications of these observations and results on the study of the fine-scale structure of interfaces are discussed.