The Effect of Grain Size and Deformation Sub-structure on Mechanical Properties of Polycrystalline Copper and Cu–Al Alloys

The grain size effect on the apparent yield and flow stresses up to 20% strain has been investigated in polycrystalline copper and Cu–Al alloys of various grain sizes at 77 and 293 K.The apparent yield stress satisfies the Hall-Petch relation in all specimens. In copper, however, the flow stresses cannot be expressed by a simple linear function but they are subdivided into two groups characterized by different linear functions of the inverse square root of the grain size. These flow stresses of copper can be roughly expressed by a single linear function of the inverse of the cell size determined by the amount of deformation, as in the case of aluminum. On the other hand, the flow stresses up to 20% strain are satisfied with the Hall-Petch relation in deformation of Cu-6.11 wt%Al alloy.The discrepancy between copper and Cu–Al alloys is discussed in terms of the effect of stacking fault energy on macroscopic and microscopic deformation modes.