TEM Orientation Mapping Applied to the Study of Shear Band Formation

Abstract

The formation of brass-type shear bands (SBs) in twinned microstructures of \({\rm C} \{ 112 \} \langle 111 \rangle \) oriented copper single crystals, has been investigated after channel-die deformation at 77 K. Setting up a system for making high-resolution orientation maps using transmission electron microscopy (TEM) has opened new advantageous circumstances for the analysis of orientation changes within SBs. This method with spatial resolution higher than 10 nm allows an examination of microstructure images composed of nanoscale sub-cells forming SBs structure. The early stages of SBs formation are the result of equally effective operation of two slip systems operating on the {111} slip planes which could be represented by a ‘resultant super-system’ of \(\{ 111 \} \langle 112 \rangle\) type. This process leads to the lattice rotation about \(\langle 110 \rangle \) axis and to the rise of Goss orientation within the band. A minor group of components is observed near \(\{ 114 \} \langle 221 \rangle \), arising from the near primary matrix orientation. For well-developed SBs, a second rotation about \( \langle 112 \rangle \) direction is observed. This tendency, resulting from the \(\{ 111 \} \langle 110 \rangle \) type slip systems operation, is usually accompanied by activation of new slip systems. Hence the process of SBs formation is regarded as a strictly crystallographic one.