First-principles study of secondary slip in zirconium

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Materials Science

Background:

• Hexagonal close-packed (HCP) metals like zirconium (Zr) exhibit complex dislocation glide behavior.
• Prismatic glide planes are typically favored for dislocations in HCP structures.
• Screw dislocations can deviate from their primary glide planes, but the mechanisms are not fully understood.

Purpose of the Study:

• To investigate the mechanisms by which screw dislocations escape their habit (prismatic) planes in HCP Zr.
• To determine the energetic pathways and thermal activation processes involved in pyramidal and basal glide.
• To elucidate the atomic configurations and intermediate states during dislocation motion.

Main Methods:

• Employed ab initio calculations to model dislocation behavior.
• Utilized the nudged elastic band (NEB) method to determine minimum energy pathways.
• Analyzed the atomic structure and energetics of dislocation configurations.

Main Results:

• Identified a shared, thermally activated process for screw dislocation escape to pyramidal and basal planes.
• Revealed an unusual conservative motion of the prismatic stacking fault perpendicular to its plane.
• Observed a nonplanar, metastable intermediate configuration involving joined stacking faults and a pyramidal twin.

Conclusions:

• The escape of screw dislocations from prismatic planes in Zr is governed by a common, surprising mechanism.
• This mechanism involves a unique stacking fault migration and a transient, complex dislocation structure.
• Findings challenge previous assumptions about dislocation mobility in HCP metals.