The candidacy of shuffle and shear during compound twinning in hexagonal close-packed structures

TL;DR

This paper develops a systematic method to calculate atomic shuffles and shear candidates in compound twinning modes of hexagonal close-packed metals, providing new analytical expressions and insights into their roles in twinning dislocation mobility.

Contribution

It introduces the first analytical formulation for atomic shuffles in non-Bravais lattices during twinning, distinguishing shuffle displacements from net shuffles and analyzing their behaviors.

Findings

Net shuffles are always rational vectors.

Shuffle displacements can be irrational for corrugated planes.

Net shuffles can vanish in certain limiting cases.

Abstract

This paper proposes a systematic generalized formulation for calculating both atomic shuffling and shear candidates for a given compound twinning mode in hexagonal closed-packed metals. Although shuffles play an important role in the mobility of twinning dislocations in non-Bravais metallic lattices, their analytical expressions have not been previously derived. The method is illustrated for both flat planes and corrugated planes which are exemplified by {11-22} and {10-12} twinning modes, respectively. The method distinguishes between shuffle displacements and net shuffles. While shuffle displacements correspond to movements between ideal atom positions in the parent and twin lattices, net shuffles comprise contributions from shear on overlying planes which can operate along opposite directions to those of shuffle displacements. Thus, net shuffles in the twinning direction can vanish in a limiting case, as is interestingly the case for those needed in the second plane by the b_4 dislocation candidate in {11-22} twinning. It is found that while shuffle displacement vectors can be irrational when K_1 is corrugated, net shuffle vectors are always rational.