First-principles study of crystallographic slip modes in ω-Zr

We use first-principles density functional theory to study the preferred modes of slip in the high-pressure omega phase of Zr. The generalized stacking fault energy surfaces associated with shearing on nine distinct crystallographic slip modes in the hexagonal omega-Zr crystal are calculated, from which characteristics such as ideal shear stress, the dislocation Burgers vector, and possible accompanying atomic shuffles, are extracted. Comparison of energy barriers and ideal shear stresses suggests that the favorable modes are prismatic < c >, prismatic-II < 10 (1) over bar0 > and pyramidal-II < c + a >, which are distinct from the ground state hexagonal close packed alpha phase of Zr. Operation of these three modes can accommodate any deformation state. The relative preferences among the identified slip modes are examined using a mean-field crystal plasticity model and comparing the calculated deformation texture with the measurement. Knowledge of the basic crystallographic modes of slip is critical to understanding and analyzing the plastic deformation behavior of omega-Zr or mixed alpha-omega phase-Zr.