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。1）从In-Tl和Na晶体的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。当样品保持在Ms以上的温度下时，第一次发现了潜伏期。2）通过对马氏体形核过程的二维计算机模拟，可以方便地将模拟结果可视化，并获得了一些重要的结果，如在形核过程中引入孪晶，以及空位在成核过程中的作用等。3）对于β 2*zeta 2'Au-49.5at%Cd合金中的（三角）相变，对于该相变的晶体学40年来一直没有解决，唯象晶体学理论的成功应用，解决了不同研究者之间关于晶格不变量剪切存在与否的巨大分歧。4）类橡胶行为的机制50多年来一直没有解决，但是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变化进行精确测量，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部变化，表明一级无扩散相变的许多基本问题已经得到解决。

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.