Positron Annihilation Study of Vacancies and Dislocations in Deformed Fe and Ni

在辐照和塑性变形过程中，材料中会产生各种缺陷，如点缺陷、位错等，从而使材料性能发生显着变化。这是一种从原子尺度到宏观尺度的多尺度现象，对总体效应的整体理解是非常困难的，尽管研究历史悠久，但仍有许多问题尚未解决。对原子学特征的研究通常是理解整个现象的基础，必须刻不容缓地进行。本研究采用正电子寿命测量、正电子寿命计算、电阻率测量、力学测试、计算机模拟等手段，对点缺陷、位错及其相互作用进行了原子学研究，以获得缺陷、缺陷簇、位错及其相互作用的基本性质。Fe和Ni的低温电子辐照和低温正电子寿命测量给出了这些金属中空位的基本性质，如第III阶段的信息，即空位迁移温度(Fe为200K，Ni为330K)。塑性变形不仅会在晶体中引入位错，而且还会在晶体中引入空位，这给理解变形材料的正电子寿命测量带来了一些困难。对于位错的正电子寿命计算通常给出很短的寿命，这与对基质的寿命非常接近，因此在实验中得到的结果必须被理解为对应于位错和空位的复合体。

During the irradiation and the plastic deformation various kinds of defects such as point defects and dislocations are generated in materials and then the prominent change of material properties takes place. This is the multi-scale phenomenon covering from the atomistic scale to the macroscopic scale and the whole understanding of the total effects is very difficult, and in spite of the long history of the research there are many problems remained unsolved. The study of the atomistic features usually gives the basis of the understanding of the whole phenomena, and must be performed urgently. In the present research the atomistic studies have been carried out for the point defects, dislocations and the interaction between them by using the positron lifetime measurement, positron lifetime calculation, electrical resistivity measurement, mechanical tests, computer simulation and so on in order to obtain the fundamental properties of defects, defect clusters, dislocations and the interaction between them. The low temperature electron irradiation of Fe and Ni and the low temperature positron lifetime measurement gave the basic properties of vacancies in these metals, such as the information of stage III, i.e., vacancy migration temperature (200K for Fe and 330K for Ni). The plastic deformation usually introduces not only dislocations but also vacancies into the crystals, and this produces some difficulties in the understanding of positron lifetime measurements for the deformed materials. Positron lifetime calculation for dislocations usually gives very short lifetimes, that is very close to that for matrix, so the result obtained in the experiments must be understood to be corresponding to the complex of a dislocation and vacancies.