Electron Microscope Study on Early Stages of Aging in Cu and Ni Base Binary Alloys Containing Be

Abstract

The changes in microstructure during the initial stages of aging in Cu-1.8 wt%Be and Ni-2.5 wt%Be alloys were systematically examined by means of electron transmission microscopy and electron diffraction technique.
It was found that during the formation and growth of G.P.zones in these two alloys there were some significant changes in details of the diffraction patterns obtained. In the earliest stage of the G.P.zone formation, the short streaks were observed in a complex manner at each of the normal diffraction spots. In the subsequent stage, the long streaks appeared along ⟨100⟩ directions, which were typical of a plate-like G.P.zone. Furthermore, the extra spots were observed at the positions of ordering reflections. In the later stage, the intensity maxima were observed on the ⟨100⟩ long streaks.
The short streaks were thought to arise from the elastic strain effects induced by the formation of the G.P.zones on {100} planes. The complex morphology of the short streaks observed was found to be given by the geometrical relation between the short streaks of the reciprocal lattice point and Ewald’s sphere of reflection.
It was also found that the appearance of the extra spots was not due to an ordered structure but due to the intersection of the long ⟨100⟩ streaks with the reflecting sphere.