The Variation of the Dislocation Density in Aluminum Deformed to Large Steady-State Creep Strains
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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This thesis reports trends in the variation of the subgrain size and density of dislocations not associated with subgrain boundaries forest dislocations in high purity aluminum with strain during primary and steady- state creep at temperatures in the power-law regime utilizing torsional deformation. Any microstructural feature responsible for strength is expected to be constant during steady-state deformation. Earlier work addressed changes in the subgrain size over a wide range of steady-state strain. A constant subgrain size was found. The present effort primarily examined the dislocation density but also further evaluated the conclusion of a constant subgrain size during steady-state. The subgrain size data were found consistent with the earlier work. In contrast to constant-stress tests in other investigations, it was found, here, that the forest dislocation density monotonically increased until a steady-state at a strain of approximately 0.20. The forest dislocation density is essentially constant at steady-state. These two findings are consistent with dislocation network theories for creep. Optical micrographs were taken from tangential sections of the torsion samples, which substantiated the finding that the subgrain size is fixed during steady-state.
- Metallurgy and Metallography