Abstract
In order to investigate whether the stagnation of strain hardening upon stress reversal which had been observed in aluminium is a general phenomenon in single phase, fcc and bcc pure metals, the strain-hardening behaviour during reversed straining of prestrained aluminium, copper and iron polycrystals was analyzed using the strain-hardening rate vs true stress relation.
In all the materials examined, the strain-hardening rate, θ, near (and/or above) the prestress was found to be lower than that obtained during prestraining. This fact implies that the strain-hardening behaviour upon stress reversal is not so simple as has been reported by Orowan. It was also found that the lowering degree of θ increased with increasing amount of prestrain (i.e., with increasing tendency toward cell structure formation). Further, thermal recovery and cyclic stressing after prestraining, which coverted the cell wall consisting of dislocation tangles into a sharp sub-boundary consisting of neat dislocation-networks, gave rise to disappearance of the stagnation. From these results the stagnation of strain hardening upon stress reversal was concluded to be ascribed to the disintegration of cell walls during reversed straining; the lowering of θ may be due to an increase both in the density of mobile dislocations and in their mean free path.
