Point defect generation, nano-void formation and growth. I. Validation

The volume fraction of point defects generated as a function of plastic shear strain squared, γ2, was derived from crystal plasticity concepts. The evolution was determined from the stress–strain values using a new constitutive relation which replicates the measured behavior with at least two fitted loci. Assuming that nano-voids form by clustering of vacancies, the nano-void diameter was found to be proportional to their spacing and shear strain with the constant being characteristic of point defect production during deformation. The predicted amount of point defect generated was validated using the previously determined resistivity of [100] copper single crystals deformed at 4.2 K and annealed at 296 K. Similar analysis of super-pure polycrystalline copper data affirmed that the dynamic annihilation parameter extrinsically incorporated in the new derivation is larger due to formation of slip clusters. Moreover, the temperature dependence of the mean slip-distance to inter-forest spacing ratio at Stage II to III transition indicates that the thermally activated drag of vacancy-creating jogs occurs above 150 K. For polycrystalline aluminum deformed at 296 K, it was concluded that the nuclei of the nano-voids were not part of the evolving dislocation array but were embedded in the grown-in microstructure. This hypothesis is pursued in the accompanying paper, Part II, and its prediction results in a criterion for ductile failure.

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