Shear band microtexture formation in twinned face centred cubic single crystals

Abstract

The formation of brass-type shear bands (SB) in twinned microstructures of medium and low stacking fault energy (SFE) metal single crystals (copper, copper–2 wt.% aluminium and silver), with initial orientation {112}〈111〉 has been investigated after channel-die deformation at 77 and 293 K. The microstructures and local orientations were characterised over a wide range of scales by convergent beam electron diffraction in a transmission electron microscope, electron backscattered diffraction in a scanning electron microscope and optical metallography. For all metals it is shown that slip initially causes a general rotation to D(4 4 11)[11 11 8 ̄ ], which is then followed by partial twinning to the D T(26 26 5)[ 5 ̄ 5 ̄ 52] orientation. Subsequent shear banding of the unstable, layered, twin structure is responsible for the development of the strong Goss {110}〈100〉 orientation within the bands. A minor group of components is observed near {114}〈221〉, arising from the near primary matrix orientation. The intensity of mechanical twinning, and therefore, the relative amounts of primary matrix and twinned material, influences the SB internal microstructure. Alloys with low SFE such as Cu–2 wt.% Al deformed at 77 K twin almost completely whereas Cu at 77 K and Ag at 293 K retain significant quantities of (re-oriented) matrix and hence a relatively strong secondary microtexture component within the brass-type bands.