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

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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.