Deformation behaviour of magnesium bicrystals with symmetrical 90° <1120> tilt grain boundaries analysed by large area EBSD mapping

Grain boundaries play a significant role in the deformation of polycrystals. Their response to deformation is however not completely understood, particularly with respect to how they accommodate lattice rotation of adjoining crystallites by changing their structure and geometry. The current study thus investigates the deformation behaviour of Mg bicrystals with 90° <1120> symmetric tilt boundary strained in plane-strain compression up to different final strains. Due to the initial soft orientation of the two crystals, activation of basal slip in each crystal gave rise to lattice rotation around the transverse direction towards the compression direction of the channel-die. Hundreds of single EBSD maps with a small step size were obtained from the GB region and stitched together to produce large panoramic maps of a macroscopic scale. Although very time-consuming, this technique has proven useful in clarifying the origin of the non-uniform deformation zones in the vicinity of the grain boundary and explains the mechanisms, by which the grain boundary was able to cope with the imposed strain before fracture. Interestingly, several variants of extension twins were observed as an additional deformation mechanism despite having negative Schmid factors. Systematic investigation of their resulting combined shear components with respect to the sample coordinate system revealed an alignment along the longitudinal direction of the channel-die, therefore justifying their nucleation.