Investigation of Martensite Ageing Effect and the Rubber-like Behavior

这种被称为“橡胶状行为”的奇怪现象是以如下方式发生的。当合金在相变后立即在马氏体状态下变形时，它是塑性的，而当它在马氏体状态下时效一段时间时，它变成伪弹性的。虽然这一现象已经被发现60多年了，但其起源仍然不清楚。为了了解这一现象的成因和机理，采用拉伸试验、DSC、四圆X射线衍射仪、内耗等技术对这一现象的特征进行了详细的研究。除Au-47.5at%Cd（正交晶）和Ti-Ni合金外，主要采用Au-49.5at%Cd合金（三角马氏体）。结果表明：1）随着时效时间的延长，孪晶临界应力、Af温度和杨氏模量逐渐升高，而内耗逐渐降低; 2）类橡胶行为是一种体积效应，而不是边界效应。 ...更多信息 3)马氏体时效效应随试样向母相逆转变而消失。4）空位的存在增强了马氏体时效效应，并认为马氏体时效效应是通过短程扩散发生的。即在空位密度很低的Ti-Ni合金中不存在时效效应。5）马氏体的平均结构和长程有序度不随时效而改变，考虑到这些特点，除了下列三个模型外，排除了迄今提出的9个模型中的大多数。i）短程有序模型（Marukawa-Tsuchiya），ii）应变偶极模型（T.Suzuki）和iii）空位相互作用有序模型（Ren和Otsuka，目前的工作）。然而，所有这些模型都有一些缺点。为了获得突破，缺陷密度（即空位和反结构缺陷的密度）的测量是非常重要的，并且对该目标的研究仍在继续。我们相信在不久的将来会得到奇异效应的解。少

The strange phenomenon called "the rubber-like behavior" occurs in the following way. When the alloy is deformed in the martensitic state right after the transformation, it is plastic, while when it is aged in the martensitic state for some time, it becomes pseudoelastic. Although the phenomenon is known for more than 60 years, the origin is still not known yet. To understand the origin and mechanism, the characteristics of the phenomenon was studied in detail by employing various techniques such as tensile tests, DSC,4 circle x-ray diffractometer, internal friction etc. The Au-49.5at%Cd alloy (trigonal martensite) was used mostly, in addition to Au-47.5at%Cd (orthorhombic) and Ti-Ni alloys. Thus, the following basic characteristics were confirmed for this peculiar phenomenon.1) The critical stress for twinning, the Af temperature and Young's modules increase, while the internal friction decreases with ageing.2) The rubber-like behavior is a volume effect rather than a boundary effect. … More 3) The effect of martensite ageing annihilates once the specimen is reverse trasformed to the parent phase.4) The martensite ageing effect is enhanced by the presence of vacancies, and is considered to occur by short range diffusion. i.e.there is no ageing effect in Ti-Ni alloy, where the density of vacancies is very low. The activation energy for the ageing effect was measured to be 0.44eV.5) The average structure and the long range order of a martensite do not change with ageing.Considering these characteristics, most of the 9 models so far proposed for the phenomenon are ruled out, except for the following three models. i) short range order model (Marukawa-Tsuchiya), ii) strain dipole model (T.Suzuki) and iii) vacancy interaction ordering model (Ren and Otsuka, present work). However, all these models have some shortcomings. To get a breakthrough, measurements of defect denities (i.e.the densities of vacancies and anti-structure defects) are very important, and the research for the goal is still intensively continued. We believe the solution for the strange effect will be obtained in the near furture. Less