Elongation Fracture of Metals Containing Pre-introduced Secondary Defects

Abstract

High-speed, high-strain tensile deformation of thin foils of fcc metals has recently been found to result in the formation of an anomalously high density of small vacancy clusters, probably in the absence of dislocations. In the present study, deformation of secondary-defect-pre-introduced pure Al is performed; at strain rates ranging from 10 m 4 to 10 5 /s and a deformation temperature of m 196 or 25°C. Microstructures in the deformed regions are examined by transmission electron microscopy. Vacancy-type dislocation loops and voids are eliminated by the deformation. He-bubbles are observed to elongate under a tensile stress, mainly in the absence of dislocations. Rows of bubbles oriented close to directions of elongation are found, and might result from extreme elongation and division of bubbles. The bubble rows are parallel to particular crystallographic directions, either d 001 ¢ or d 112 ¢ . This indicates that displacement of atoms during high-speed, high-strain tensile deformation progresses while conforming with the nature of a crystal, even in the absence of dislocations.