Substructures of deformation twins and twin intersections in a Ti-45Al-8Nb-2.5Mn alloy heavily deformed at room temperature

Substructures of deformation twins and twin intersections have been investigated by transmission electron microscopy (TEM) in a heavily-deformed Ti-45Al-10Nb-2.5Mn (at.%) alloy. The deformation twins become severely bent after blocking numerous matrix dislocations. The (111)(DT) plane in the twins exhibits a misorientation angle with the (111)(M) plane in the matrix, and numerous 1/3[111] Frank partial dislocations appear in the twin boundaries. Furthermore, the barrier twins also become bent after being intersected by numerous incident twins. The barrier twin boundaries in two types of twin intersections show different tilting directions due to different orientations of the incident twinning dislocations relative to the barrier twins. Some special nano-scale substructures appear simultaneously at the intersection area in order to relax the large stress concentration of several twin-band intersections. The propagation of several incident twin tips in the same direction could induce the formation of small-angle tilting grain boundaries in the intersection area of the type-I. The opposite propagation of several incident twin tips could induce a triangular striated region near the intersection area. Some nanotwins nucleate and propagate with a homogeneous twinning shear mechanism, and were limited mostly in the triangular striated region. (C) 2001 Elsevier Science B.V. All rights reserved.