Formation of brass-type shear bands and their influence on orientation changes of Cu-2%Al alloy (112)⟨111⟩ single crystals

Microstructural and microtextural aspects of the "brass-type" shear bands formation in twinned microstructures of low stacking fault energy (SFE) copper-wt 2%Al single crystals, with initial orientation {112}<111> have been analysed after channel-die deformation at 77 and 293 K. The microstructures and the local orientation changes were characterized mainly on the longitudinal sections over a wide range of scales by TEM, SEM and optical metallography in conjunction with SEM/EBSD and TEM/CBED microtexture measurements as well as X-ray diffraction for the global texture determination. In both deformation terms, the crystals first rotate by slip towards D(4 4 11)[11 11 (8) over bar]. Subsequent deformation twinning transforms the previous group of orientations into the D-T(26 26 5) [(5) over bar (5) over bar 52] one. As shear banding starts, a strong increase of intensities near the Goss {110}<100> position is observed, and this process is connected with (+)TD of the twin lamellae rotation within shear bands. Additionally, in TEM scale, the occurrence of the second weaker component near {114}<221>(M), connected with the position of the primary matrix inside the shear band, is noticed. Outside the bands the twin-matrix lamellae show opposite, (-)TD rotation and the material reorients to {111}<112>(T,M).