On the energetics of flickering contrast observed in TEM images of an aged 53Cu45Mn2Al damping alloy

Abstract

Video imaging techniques were applied to transmission electron microscope images in order to investigate the motion of the spatially consistent and repetitive contrast variations (termed flickering) observed in an aged CuMnAl dampig alloy. A fiber optic light sensing probe was coupled with a spectrum analyzer to determine the frequency characteristics of the flickering activity directly from a video screen connected to the TEM. The effects of specimen temperature and TEM beam current were studied. Certain flickering sites exhibit peaks in the magnitude of contrast change at specific frequencies. The peaks in the frequency spectrum vary in amplitude and, to a lesser extent, in frequency, with specimen temperature and with TEM beam current. Detailed examination of the real-time behavior at the flickering sites suggests that the underlying mechanism which produces the contrast change is a gradual crystallographic transition, typical of a second order phase transition. As well, the patterns of change which comprise the flickering contrast display many of the characteristics of “chaotic vibrations”.