Change in the Bauschinger effect during the relaxation of twinned crystals

Changes taking place in the quantitative characteristics of the Bauschinger effect in wedge-shaped twins are studied in relation to the period for which these are held before untwinning. All the measurements are made in the cleavage plane of single-crystal zinc and Zn-Cu alloys. The Bauschinger displacement of the twin boundaries first increases slightly and then starts diminishing during the delay period. In the course of untwinning, the region of easy untwinning on the (b) relationship diminishes with time in the softened zone; the extent of the softened zone remains constant during the relaxation of the crystals. The suppression of the Bauschinger effect takes place more intensively if the crystal is held under load before untwinning. The change in the quantitative characteristics of the Bauschinger effect may be explained by the diffusion of impurities to the twinning dislocations and dislocation sources and the consequent blocking of these, and also by the relaxation of stresses in the twin boundaries as a result of plastic shears and dislocation reactions between complete and twinning dislocations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 113–117, April, 1971.