Structural evolution in pure polycrystalline samples was studied by multiple compression at room temperature. Rectangular specimens were compressed, with a change in the loading direction from pass to pass. The deformation behaviour at strains greater than 2 revealed an apparently steady-state flow which followed a rapid increase in the flow stress in the early stages of deformation. The structural changes were characterized by the evolution of many mutually crossing sub-boundaries at low to moderate strains; followed by the development of very fine grains having medium- to high-angle boundaries at large strains. The new grains were suggested to develop via a form of continuous reaction: continuous dynamic recrystallization. The grains which developed during continuous dynamic recrystallization were much finer than was expected upon extrapolating discontinuous dynamic recrystallization data on hot deformation. An average grain size of about 0.2μm developed at room temperature, and this was roughly similar to that for sub-grains which developed at the preceding strains.

Grain Refinement in Copper under Large Strain Deformation. A.Belyakov, T.Sakai, H.Miura, K.Tsuzaki: Philosophical Magazine A, 2001, 81[11], 26-43