Atomistic simulation of shear in a martensitic twinned microstructure

Molecular-dynamics simulations are used to apply shear to the twinned microstructure of an hcp metal, represented by a Finnis-Sinclair-type potential for zirconium. The twinned microstructure results from a simulated martensitic phase transition from the high-temperature phase, and hence contains some boundary defects. The $60\ifmmode^\circ\else\textdegree\fi{}$ twin boundary can be regarded as a $(101\ifmmode\bar\else\textasciimacron\fi{}1)$ symmetric tilt boundary with partial twin boundary dislocations. These are sessile, but act as sources for the boundary steps which allow the boundary to migrate. Once the twinning deformation mechanism is exhausted, the partial twin boundary dislocations remain as lattice dislocations, and can move under further shear.