Deformation Twinning in Cu-5.0 at%Si Alloy Single Crystals in the Compressive Test

Abstract

Cu-5.0 at%Si alloy single crystals having various orientations were tested at −196°C in compression. In this work, the characteristics of deformation twinning were investigated and compared with those of the previous works in the tensile test. The results are summarized as follows.
(1) The onset of twinning in the compressive test is characterized by a bent in the stress-strain curve and a formation of twin bands observed by optical microscopy. Also, it has been observed by transmission electron microscopy that the twin band contains many individual fine twin lamellae and the width of these lamellae are about 0.1μ.
(2) The twinning systems in the compressive test are (111)[11\bar2] and (\bar111)[\bar11\bar2], but these systems are different from that in the tensile test, namely (111)[\bar211] and (\bar1\bar11)[\bar121]; this behavior is explained by the concept of polarization of shear, i.e., unidirectionality of twinning.
(3) In the compressive test by 10% strain, the region showing twinning in the stereographic triangle is limited to the orientations near [001].
(4) The orientation dependence of the twinning in the compressive test cannot be explained in terms of the dislocation reaction proposed by Venables and Cohen et al.