New developments on displacive phase transformations

对于本组研究的五个主题，每个主题都描述了结果的摘要。(A)一阶位移相变的机制：在马氏体相变之前，利用“平行六面体共振法”系统地测量了Ti-Ni合金系(Ti-Ni，Ti-Ni-Cu，Ti-Ni-Fe)的弹性常数。结果发现，这三种马氏体相变与弹性常数的温度依赖性(c‘，c&t；44&gt；)和弹性各向异性(A≡c&lt；44&gt；/c’)之间存在着密切的关系.(B)晶格缺陷与一阶位移相变的相互作用：通过引入“对称-协调短程序原理”(自然，1997年)，一致地解释了长期存在的“橡胶行为”这一问题的所有方面.此外，“微结构记忆”和“双向形状记忆”效应等新现象也出现了…现象基于这一原理(Phys.Rev.Lett，2000)得到了更多的发现。(C)一阶位移相变热力学的新方法：对于统一处理非热和等温马氏体相变的Kakeshita理论，进行了系统的实验。(D)薄膜中的一阶位移相变：用透射电子显微镜系统地研究了溅射沉积技术制备的Ti-Ni薄膜的结构。结果发现，随着成分和时效温度的变化，存在五种析出态。(E)纳米合金颗粒中的一级位移相：用透射电子显微镜原位观察到了Au-Cd和Fe-Ni合金纳米颗粒的马氏体相变。利用一种新研制的直接连接电子显微镜和真空蒸发室的装置。结果发现，合金的相变温度显著降低，但其原因不能用以前的理论解释。较少

For the five themes studied in this group, the abstracts of the results are described for each theme.(a) The mechanism of 1st order displacive transformations : The elastic constants of Ti-Ni alloy system (Ti-Ni, Ti-Ni-Cu, Ti-Ni-Fe) were measured systematically by utilizing "the parallelepiped resonance method" prior to the martensitic transformations. As a result, close relations were found to exist between the three kinds of martensitic transformations and the temperature dependence of elastic constants (c', c_<44>), and elastic anusotropy (A ≡ c_<44>/c').(b) The interaction of lattice defects with 1st order displacive transformation : The all aspects of the long-standing problem of "rubber-like behavior" was consistently explained by introducing "SC-SRO (Symmetry-Conforming Short Range Order) principle" (Nature, 1997) with respect to point defects upon displacive transformation. Furthermore, other new phenomena such as "microstructure memory" and "two-way shape memory" effects were … More found based on this principle (Phys.Rev.Lett., 2000).(c) New approach to thermodynamics of 1st order displacive transformations : For Kakeshita's theory, who treated athermal and isothermal martensitic transformations in a unified manner, systematic experiments were carried out. Thus the theory was justified by showing that an isothermal transformation will change into athermal one under magnetic field, and an athermal one into an isothermal one under hydrostatic pressure etc.(d) 1st order displacive transformations in thin films : The structures of Ti-Ni thin films produced by sputter-deposition technique were systematically studied by TEM.As a result, five precipitation states were found to exist as a function of composition and aging temperature.(e) 1st order displacive transformations in nanometer-sized alloy paricles : The martensitic transformations of nano-particles of Au-Cd and Fe-Ni alloys were observed in-situ by TEM, by using a newly developed apparatus directly connected TEM and vacuum evaporation chamber. As a result, the transformations temperatures of the alloys were found to decrease greatly, but the cause was found not to be explained by the previous theory. Less