Changes in interface parameters and tensile properties in copper as a consequence of iterative processing

Both one-step and subsequent multistep grain boundary engineering processing of copper have been investigated. Specimens were tensile tested to failure after each stage of processing, and the microhardness was measured. These properties were linked to measurements of both the grain boundary misorientation and grain boundary plane distribution in order to provide insight into the mechanisms of microstructure evolution. Analysis of the stress-strain behavior revealed the balance between deformation and microstructure restoration occurring during processing. An increase in work hardening and a reduction in ductility were observed with successive processing iterations, indicating an accumulation of retained strain. This brought about stagnation in the microstructure, whereby no new Sigma 3s were generated and grain boundary migration was stabilized. It was shown that Sigma 3 boundaries are effective agents for dislocation pileup, and this strain-retention ability plays an important role in the early stages of iterative processing. Analysis of the data in terms of incorporated and nonincorporated Sigma 3s indicated that iterative treatments are mechanistically different from one-step treatments. It was also shown that the Sigma 9 and Sigma 27 boundaries added to the microstructure as a consequence of iterative processing were not special, because they were on irrational boundary planes.