Three-dimensional atomic scale characterization of {11(2)over-bar2} twin boundaries in titanium

The {11 (2) over bar2} < 11<(23)over bar> > compression twin can accommodate a considerable amount of strain under c-axis compression in Ti. However, unlike the tensile {10 (1) over bar 2} <(1) over bar 011 > twin, the structure of {11 (2) over bar2} < 11<(23)over bar> > compression twins has not been completely characterized. Here, we apply a combined technique of HRTEM characterization, topological analysis, and atomistic simulations to explore the facets that bound the {11 (2) over bar2} < 11<(23)over bar> > twin in Ti. In addition to the currently known facets (CTB and B-Py), six new facets are observed and categorized for the first time from atomic-scale TEM observations along five crystallographic directions. The six new facets are (11 (2) over bar0)//(11 (2) over bar6), PrPr1, PyPy1, (2 (11) over bar1)//((1) over bar2 (1) over bar1), (1 (1) over bar 04)//(01 (11) over bar), and (01 (1) over bar0)//(2 (11) over bar4). Results from the topological and computational analysis are in reasonable agreement with and support the HRTEM observations. Specifically, (1) the observed facets align with low-index interfaces in both twin and matrix domains, (2) the facets with lower surface energies are found to form extended interfaces, and (3) high-surface-energy facets are found at the twin tip region and explained by the fact that the energy of the combined facet and facet junction configuration is energetically preferred in the twin tip region. These results not only provide a comprehensive understanding of the 3D structure of {11 (2) over bar2} < 11<(23)over bar> > compression twins in Ti, but also validate the MD procedure and the Ti interatomic potential employed. This is extremely important for future study of {11 (2) over bar2} twin mobility and interactions with other defects, both features that remain extremely challenging to capture in experiments. Published by Elsevier Ltd on behalf of Acta Materialia Inc.

Automated summary

A comprehensive study explored the facets that bound the compression twin in Ti, observing six new facets and validating the results through HRTEM observations and atomistic simulations. The new facets align with low-index interfaces, with those having lower surface energies forming extended interfaces, while higher surface energy facets are located at the twin tip region. These findings provide a better understanding of the 3D structure of compression twins in Ti and validate the MD procedure and Ti interatomic potential used in the study.