Detwinning of face-centered cubic deformation twins at liquid nitrogen temperature

The paper brings experimental results on low temperature (77 K) detwinning of deformation twins of the twin/ matrix layered Cu-8at.%Al microstructure pre-created during room temperature plastic deformation. It was found that the 297 K -> 77 K temperature change does not cause any perturbation to potential activity of all three face-centered cubic detwinning modes. It means, the reverse mode (pi) and the two pseudo-reverse modes (+/-pi/3) of deformation twinning. These detwinning systems strongly contribute to the low temperature crystal plasticity of the twin/matrix structures controlling their extraordinary mechanical properties, i.e., large anisotropy and asymmetry of the tension/compression yield stress. As suggested, the effective increase of critical stresses of the detwinning modes, due to the temperature lowering, is caused by the combine effect of thermally assisted interactions of detwinning dislocations with the dislocation obstacles and the enhancement of internal stress field. The latter being directed in the pre-twinned material along the shear vector of the pi detwinning mode. The obtained results point to the significant role that face-centered cubic detwinning shall play in design of many technological processes of large plastic deformation occurring at low temperatures, e.g., cold rolling of TWIPtype materials.