Observations of the Atomic Structure of Tensile and Compressive Twin Boundaries and Twin-Twin Interactions in Zirconium

The boundary structures of twins in the hexagonal close-packed metal zirconium were studied. High-resolution transmission electron microscopy was used to characterize the boundary structure of (T1), (T2), and (C1) twins on the atomic level. Basal-prismatic (B-P) plane faceting is observed along the T1 twin boundaries, matching previous observations of T1 twins in magnesium. C1 twins are observed to form basal-pyramidal (B-Py) facets along otherwise perfect twin planes. T2 twins exhibit faceting that aligns prism planes with second-order pyramidal planes across the boundary (P-Py facets). As a function of the crystallography, T2 twins appear less likely to accommodate large deviations from perfect twin planes by P-Py faceting alone, and may rely on small dislocation-accommodated facets to achieve arbitrary boundary planes. The structure of these boundaries, specifically the modes by which faceting is permitted, has a direct impact on boundary mobility. In addition, the boundary structure of two C1 twins during a twin-twin interaction event is observed, and is compared to previous observations of tensile twin-twin interactions in magnesium.