Title

Measurement of dislocation velocities and mobile dislocation densities as a function of strain and strain rate in cadmium single crystals

Date of Completion

January 2003

Keywords

Engineering, Metallurgy|Engineering, Materials Science

Degree

Ph.D.

Abstract

Instantaneous dislocation velocities and associated dislocation densities were measured in situ while cadmium single crystals were being plastically deformed. These measurements exploited the interactions between electrons and dislocations, brought about by the application of a magnetic field. During the deformation of the cadmium crystal at 4.2 K, a magnetic field was rotated through the active slip plane of the crystal, resulting in a change (maximum) in the deformation stress. These maxima were observed only when the crystal is deforming plastically, only when the magnetic field passes through the slip plane and only when the electrons are the dominant drag force on the dislocations, occurring only at low temperatures. Measurements of these maxima as a function of plastic strain show that they consist of two types of peaks. Single sharp peaks were observed predominantly at lower values of strain and two broad peaks, symmetrically arranged about the angle corresponding to the measured angle that the slip plane makes with the tensile axis, were observed predominantly at higher strain. These results were compared with treatments of electron-dislocation interactions and were consistent with the viscous drag process controlling the dislocation motion. ^