The effect of temperature on detwinning and mechanical properties of face-centered cubic deformation twins

Inverse temperature dependences of the detwinning stress of face-centered cubic deformation twins were discovered by studying the effect of elevated temperatures on plastic deformation properties of multilayer twin/ matrix structure of the Cu-8at.%Al alloy. The critical stress of detwinning was found to increase remarkably with temperature when plastic yielding of the twin/matrix structure occurred by the pi detwinning mode. However, when the alternative pi/3 mode of detwinning was involved, a decrease of the detwinning stress with an increase of temperature was observed, instead. Thus, the twin/matrix structure behaved in two opposite ways, showing anneal hardening (the case of pi mode) or anneal softening (the case of pi/3 mode) upon temperature increase. As concluded, the dual effect of temperature on the detwinning stress resulted from irreversible reduction of internal stresses pre-existing within the deformation twins. The complete reduction of the internal stresses at about 530 degrees C led to the equivalence of the critical stresses of different detwinning modes and a large decrease of the yield stress anisotropy of the twin/matrix structure. It was postulated that temperature induced annihilation of the internal stresses resulted from constriction of extended cube dislocations pre-existing within deformation twins. The temperature limit of about 540 degrees C, beyond which the twin/matrix structure became unstable due to recrystallization, was also established. Moreover, transfer of plastic shear throughout the twin/matrix structure was found to be predominantly controlled by internal dislocation substructure of deformation twins, not by the twin/matrix interfaces.

Automated summary

Inverse temperature dependences of the detwinning stress were observed in face-centered cubic deformation twins in Cu-8at.%Al alloy. The detwinning stress increased with temperature when the pi detwinning mode was involved, but decreased when the pi/3 mode was involved. The dual effect of temperature on the detwinning stress was due to the reduction of internal stresses pre-existing within the deformation twins. The complete reduction of internal stresses at about 530 degrees C led to the equivalence of the critical stresses of different detwinning modes and a decrease in the yield stress anisotropy of the twin/matrix structure.