Fig. 4
Twin intersection toughening. a Crack deflection event (CDE) #6 taking place at a boundary with low-index plane (BLIP) created by the impingement of a twin lamella on a grain boundary (GB). b A 2D section through the 3D reconstruction in a showing traces of the incoming, deflected, and grain boundary planes (see schematic Fig. 2b) as well as values of the dihedral angles, θcrack and θresist, used to identify the CDE. Solid arrows indicate the path of the crack, the dashed line indicates the nominal crack direction, and the dotted arrow indicates the path along the crack-resistant boundary that deflected the crack. The angles indicated are the dihedral angles defined in Fig. 2b. Scale bar: 50 μm. c, d Schematic showing the role of twin lamellae in altering the crack-propagation resistance of GBs. c A crack reaching a triple junction propagates along a low-toughness GB that is aligned well with the crack plane. d A twin lamella intersecting the GB locally alters the GB character, creating a BLIP that arrests the propagating crack and deflects it onto a different, more tortuous path
