In-situ Straining Experiments in the Hish Voltage Electron Microscope to Study Precipitation Hardening

Abstract

The paper reviews in-situ straining experiments in the high voltage electron microscope on precipitation-hardened MgO, Al-Zn-Mg, Al-Ag, and Al-Li. Dislocations under stress bow out between the precipitates. The distances between the obstacles along the dislocation lines and the curvatures of the bowed-out segments are measured from the electron micrographs. The density of obstacles in the slip plane and the effective stress are calculated from the data. The density agrees or disagrees with the results of other investigations, mainly conventional TEM of the precipitates. From plots of the reciprocal dislocation curvature versus the logarithm of the segment length it is concluded that the dislocations are far more flexible than expected from theory in all materials investigated