Effects of normal stress, surface roughness, and initial grain size on the microstructure of copper subjected to platen friction sliding deformation

The effects of applied normal stress, surface roughness, and initial grain size on the microstructure of pure Cu developed during platen friction sliding deformation （PFSD） processing were investigated. In each case, the deformation microstructure was characterized and the hardness of the treated surface layer was measured to evaluate its strength. The results indicated that the thickness of the deformed layer and the hardness at any depth increased with increasing normal stress. A smaller steel platen surface roughness resulted in less microstruc- tural refinement, whereas the microstructural refinement was enhanced by decreasing the surface roughness of the Cu sample. In the case of a very large initial grain size （d 〉 10 mm）, a sharper transition from fine-grain microstructure to undeformed material was obtained in the treated surface layer after PFSD processing.

Analysis of Stored Energy in Cold-Rolled Copper Using Bulk and Microstructure-Based Techniques

Measurements of stored energy have been obtained for samples of copper cold-rolled to von Mises strains between 0.42 and 5.21 using both differential scanning calorimetry （DSC）, and based on measurements of microstructural parameters in the transmission electron microscope （TEM）. In both cases, a linear increase in stored energy with strain is found. The ratio between the two measured values varies, however, over a significant range, indicating that some caution is needed in determining the relative difference in energy associated with deformation microstructure heterogeneities in a given sample. Comparison of the stored energy with the flow stress suggests that the TEM-based measurements reflect the dislocation density content responsible for the flow stress, but that the DSC technique additionally measures other contributions to the stored energy, such as the presence of balanced internal stresses.