Kinetics of Formation of Mesoscopic Scale Patterns in First Order Phase Transition of Alloys

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A high sensitive CCD video camera was installed in a transmission electron microscope,and processes of first order phase transition of various alloy systems which are not fully traced by taking conventional still micrographs because of the quickness are recorded on video-tapes,and the data obtained are analyzed by computer image processing. The results are in the following.1. Macroscopic patterns of bcc(bct) martensite of Fe-30at%Pd alloy are arrangements of variant crystals due to self-accommodation to attain compatibility at grain boundaries of the pre-existing austenite.2. Characteristic mottled contrast in bcc(bct) martensite of Fe-30at%Pd alloys is associated with strain contrast by partial clustering of Pd atoms in the austenite and lattice invariant strain by twinning.3. Thermoelastic martensite transformation from austenite to fct of an Fe-30at%Pd alloy exhibit a characteristic mesoscopic scale contrast change from tweed to microtwins. Image processing of high resolution electr … More on micrographs of tweed indicates that distorted and undistorted regions form altemating layers parallel to {011} planes, and the distorted regions contain tetragonaly distorted static strain centers.4. Strain contrast with a mesoscopic scale in an early stage of ordering of FePd alloys corresponds to a competing state between dynamical and chemical equilibrium of the system.5. Temperature dependence of formation of radiation induced secondary defects and precipitates of Ni and Au alloys is measured by in-situ observations of an ultra high voltage electron microscope. Interaction energies of solutes with radiation formed point defects are determined,and the contrast change with elapse of times is discussed on the fluctuation of solute concentration with irradiation.6. In-situ observation of first order phase transition of an equi-atomic FeRh alloy clearly shows movements of boundaries of ferromagnetic and antiferromagnetic phases with change in temperature. The variation of transition process with annealing at 1000K is originated from fine precipitates,the formation of which is not explained by phase diagrams so far. Less