DISLOCATION MOBILITY AND INTERACTIONS IN HIGH PURITY MAGNESIUM. Interim Technical Report No. 1

Technical Report · Sat Dec 15 04:00:00 EST 1962

OSTI ID:4728658

Roblin, M J; Ansell, G S

Transmission electron microscopy was utilized to study the role of crystal structure upon slip as a plastic deformation process in high purity polycrystalline thin foils of magnesium. The effect of stress on the mobility of wholiy contained basal dislocations was investigated, using sequential and cine photography. A relationship was derived for such dislocations moving through the lattice with a constant velocity and it was utilized to show that the applied stress is not related to the velocity as reported by previous investigators. It was suggested that a stress velocity relationship should exist only between the lattice resistance stress and the velocity. A method of determining the lattice resistance stress was put forth for a specialized case of a moving dislocation array. An example of such a case was shown, and the lattice resistance stress calculated for a particular dislocation velocity. The operating slip planes were investigated by observation of moving dislocations or their traces, coupled with selected area diffraction. Five different slip planes were identified and the burgers vectors were deduced from crystallographic considerations. The diffraction patterns which were solved for the determination of the operating slip planes provided information about the plane of the foil surface. An unusual recrystallization texture was noted, and the information was plotted on a standard stereographic triangle. Simple twist boundaries were observed which provided information about the stacking fault energy of magnesium. The frequency of cross-slip correlated well with the estimate of the stacking fault energy, and on this basis the possible cross-slip plane for several slip planes was deduced. Dislocation tangles were observed in many other metals and generally occur in thicker sections of the foils where the image forces are reduced. This was found to be true for magnesium, and while the tangles complied with the observations of others, they were not observed to form upon straining, but existed in the foils after recrystallization. Grain boundary sliding was studied primarily by cine photography techniques. A model for sliding is presented on the basis of the observations made in this thesis. The proposed model correlates well with the quantitative studies of the phenomena made by other investigators. (auth)

• Research Organization: Rensselaer Polytechnic Inst., Troy, N.Y.
• NSA Number: NSA-17-011182
• OSTI ID: 4728658
• Report Number(s): AROD-3394.1
• Country of Publication: United States
• Language: English

Related Subjects

CRYSTALS
DEFECTS
DEFORMATION
DIFFRACTION
DISLOCATIONS
ELECTRON MICROSCOPY
GRAIN BOUNDARIES
IMPURITIES
LATTICES
MAGNESIUM
METALS, CERAMICS, AND OTHER MATERIALS
PHOTOGRAPHY
QUANTITATIVE ANALYSIS
RECRYSTALLIZATION
SHEETS
SLIP
STABILITY
STRESSES
SURFACES
VELOCITY