Recovery in deformed copper and nickel single crystals

Abstract

The static recovery behaviour of copper and nickel single crystals deformed in multiple slip was investigated in mechanical tests and in HVEM in situ annealing experiments. Recovery of Type I, as previously identified in aluminium was observed in both its microscopic and macroscopic features: a sharpening of the cell-wall structure without a change in substructure scale, correlated with a short transient in the strain-hardening behaviour during retesting. The substructure development with increasing recovery time and temperature is similar to that during dynamic recovery, i.e. with increasing strain in a continuous test. After longer recovery times or at higher annealing temperatures, the specimens recrystallize; after larger strains, they recrystallize dynamically. An intermediate stage akin to the Type II recovery found in aluminium was never observed, either in its macroscopic manifestation of a long reloading transient, or as a general coarsening of the subgrain structure. Examples of local sub-boundary mobility and dissolution were, however, seen in situations close to static or dynamic recrystallization. It is concluded that the fluctuations occurring during subgrain coarsening are stable in aluminium, leading to Type II recovery and extended steady-state deformation, but unstable in copper and nickel, leading to static or dynamic recrystallization.