Toward understanding twin-twin interactions in hcp metals: Utilizing multiscale techniques to characterize deformation mechanisms in magnesium

The mechanical properties of hexagonal close-packed (hcp) metals depend heavily on both slip and twinning, and interactions between twins have important implications on hardening behavior. Electron backscatter diffraction (EBSD), as well as conventional, in situ straining, and high resolution (HR) transmission electron microscopy (TEM) are used to study these interactions. HRTEM is used to observe the twin boundary structure. Twin boundaries that deviate from the characteristic {101¯2} twin planes at the macroscale are revealed to be a combination of perfect {101¯2} boundaries and characteristic facets at the nanoscale. Faceting for tensile {101¯2} twins adopts basal-prismatic (B-P) character, where basal planes in the matrix very nearly align with prism planes in the twin, or similarly, prism planes in the matrix align with basal planes in the twin. Such features play a significant role in twin boundaries, where faceting accommodates the large changes to boundary shape observed. in situ straining is used to study twin-twin interactions as they occur, and also detwinning behavior upon load reversal. During the initial interaction, considerable changes to the shape of the twin boundaries are observed, consistent with post-mortem analyses. On load reversal, detwinning is observed, and the interacting twins disengage from one another, however a change in boundary structure due to the interaction is retained.