Growth kinetics and orientation dependence of dislocation loop, in electron irradiated aluminum

Abstract

Quantitative studies show that the defect cluster production and growth rates, as a result of 200 kV electron irradiation of aluminum, are strongly influenced amongst several factors by crystal thickness, crystal orientation, impurity content and room temperature vacancy mobility. Strong evidence of vacancy mobility is obtained from the very low point defect retention ratio observed experimentally. Considerable insight into the defect production and retention process can be obtained by an analysis of the dislocation loop growth rate data according to models based on chemical reaction rate theory. As a result, the migration energy for free interstitials in aluminum is estimated to be 0.06 eV, while with strong interstitial-impurity binding the migration energy is 0.4 eV. Analysis of the electron irradiation data in aluminum suggests that interstitial-impurity binding controls defect cluster nucleation. Further evidence for this is obtained by comparing the surface denuded zone width calculated by assuming interstitial-impurity binding with that observed experimentally. Dislocation loop growth rates analyzed according to the kinetic models show that the surfaces influence the initial loop growth while bulk behavior is approached at a later state. There is considerable orientation dependence of damage observed between the and orientations. Maximum damage rates are observed at exact low index orientations with sharp drop offs by a factor of ∼ 3 when the crystal is tilted 3-5° away from these orientations.