LATENT HARDENING IN ALUMINUM.
Interim technical rept.,
HARVARD UNIV CAMBRIDGE MA DIV OF ENGINEERING AND APPLIED PHYSICS
Pagination or Media Count:
The flow stresses and the initial work-hardening slopes in all 24 slip systems were measured by isoaxial compression tests on plates cut out of aluminum single crystals which had previously been deformed in single slip to a standard stress in stage III. The flow stress results fell into two groups all slip systems with the same slip plane as the primary were, within the scatter, indistinguishable from the primary slip system all other systems fell, with no further distinction discernible, into a large group with a flow stress raised by 10 to 30. In the latter group, the initial hardening slope was usually lower than in the primary system. In only one system, corresponding to obtuse cross-slip, was a negatibe initial hardening slope ever observed. The rate sensitivity of flow stresses and of hardening sloped was measured in 9 secondary systems and was indistinguishable from that of the primary system. The results on flow stresses may be interpreted by postulating that the moving dislocations surround rather than overcome the obstacles in their path, and that the obstacles generated during the previous single slip are arranged in a pattern which distinguishes the slip plane. Furthermore, this arrangement must be polarized, since some initial hardening slopes were found to depend on the sign of the strain. A qualitative connection between the initial work-hardening sloped in secondary slip systems and the orientation dependence of primary workhardening is established. Author