Atomistic studies were made of the deformation mechanisms occurring in the crack-tip region during low temperature fracture of hexagonal close-packed Zr. Static simulations of mode I fracture in Zr single crystals were performed using empiric embedded atom potentials. Cracks were introduced in six different crystallographic orientations. For each crack orientation two different crack-propagation directions were chosen. Plasticity on the crack tip in single crystal hexagonal close-packed Zr depends strongly on the orientation of the crack. Several competing processes were involved, including the phase transformation to the body-centered cubic structure. Twinning and dislocation emission were the other major mechanisms responsible for ductility. For the cases where the transformation to body-centered cubic was observed, a significant improvement in ductility results from the transformation.

Twinning and Phase Transformations in Zr Crack Tips. M.Ruda, D.Farkas, G.Bertolino: Computational Materials Science, 2010, 49[4], 743-50