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

1994年3月17日至19日，在墨尔本附近举行了一次关于一阶无扩散相变的研讨会，以总结和评估我们联合研究的结果。每个主题的简要报告如下：1)从In-Tl和Na晶体随温度变化的X射线漫散射测量中，发现在马氏体相变之前没有预相变现象。当标本在ms以上的温度下保存时，首次发现了潜伏期。2)通过对马氏体形核过程进行二维计算机模拟，可以很容易地将结果可视化，并获得了诸如孪晶在形核过程中的引入，以及空位在形核过程中的作用等重要结果。3)对于Au-49.5at%Cd合金中的β2*zeta 2‘(三角)相变，其晶学40年来一直没有得到解决，成功地应用了唯象晶体理论。解决了不同研究者对是否存在晶格不变剪切的较大分歧。4)橡胶类行为的机制50年来一直没有得到解决，但Lieberman和Tadaki提出了两种机制。通过对几种衍射强度随老化时间的精确测量，发现积分强度基本上不随时间变化。结果否定了平均结构的变化，从而否定了Lieberman和Tadaki的机制，并提出了空位迁移等引起的局域变化。上述结果表明，解决了一阶无扩散相变的许多基本问题。

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.