The mechanism of coupled migration and shear is studied in a range of [0001] tilt boundaries in hexagonal close-packed metal using
atomic-scale computer simulation. Symmetrical tilt boundaries spanning the low- and high-angle regimes and comprising regular arrays
of grain boundary dislocations are simulated. For each misorientation, h, the perfect boundary (pristine) is investigated as well as one
containing a disconnection. Both types of structures are subjected to incremental applied strains to determine the stress that produces
coupled migration and shear. The stress for motion in the pristine case, entailing nucleation, is higher than the Peierls stress for motion
when disconnections are present. We conclude that the applied stresses in our simulations exert a Peach–Koehler force on pre-existing
disconnections, thereby providing a feasible mechanism with a well-defined driving force that produces coupled migration and shear.
This mechanism is feasible for the lower-angle boundaries studied, and facile for the high-angle cases.
 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.