Research of the First Order Diffusionless Phase Transformations on Atomic and Microscopic Scales

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A workshop on the 1st Order Diffusionless Phase Transformations was held near Melbourne from March 17 to 19, 1994, to summarize and assess the results of our joint research. A brief report on each theme is given below.1)From the x-ray diffuse scattering measurements of In-Tl and Na crystals as a function of temperature, it was found that there is no pretransformation phenomenon prior to the martensitic transformation. When specimens are held at a temperature above Ms, the incubation periods were found for the first time. The observations will be very important for the further development of transformation kinetics.2) By carrying out 2-dimensional computer simulations of martensite nucleation, easy visualization of the results was possible, and important results were obtained such as the introduction of twins in the nucleation process, and the role of vacancies in the nucleation process etc.3)For the beta 2*zeta 2'(trigonal) transformation in the Au-49.5at%Cd alloy, for which the crystallography of the transformation remains unsolved for 40 years, the phenomenological crystallographic theory was successfully applied, and the big discrepancies between different investigators on the presence or absence of the lattice invariant shear was resolved.4)The mechanism of the rubber-like behavior remains unsolved over 50 years, but two mechanisms were proposed by Lieberman and Tadaki. By carrying out accurate measurements of several diffraction intensities with aging time, the integrated intensities were found essentially not to change with time. The results deny the change of average structure, thus denying the mechanisms of Lieberman and Tadaki, and suggests the local change due to vacancy migrations etc.The above results show that many of the fundamental problems on the 1st order diffusionless phase transformations have been solved.