Lattice correspondence analysis on the formation mechanism for partial stacking faults in hexagonal close-packed metals

Abstract

Partial stacking faults (PSFs) have been frequently observed inside {101-1} and {101-2} twins in hexagonal close-packed (HCP) metals. Formation of PSFs, first described by Song and Gray, only displaces atoms on every other basal plane, in stark contrast to conventional SFs created by Shockley partial dislocations in which a global displacement vector can be defined. To experimentally verify this process is challenging. To understand the formation mechanism of the PSFs, in this work, we performed lattice correspondence analysis in atomistic simulations of {101-1} and {101-2} twinning modes in Mg, Ti and Co. In this strategy, the corresponding planes of the parent to the prismatic plane of the twin were pre-selected and tracked before and after twinning. Then, the atomic positions were examined to reveal atomic stacking position change in the twin due to the formation of the basal SFs. The results show that, indeed, only those atoms on every other basal plane are displaced by the formation of PSFs, indicating that no global displacement vector can be defined and no dislocation activities are involved in the formation of PSFs. Thus, the proposition of PSF is validated. A special configuration of PSFs was observed, which has limited mobility via coordinated atomic shuffles. A detailed analysis on the structural differences between I1, I2 stacking faults and PSFs was provided. The formation mechanism of PSFs can be extended to other HCP metals.