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 investi gated by transmission electron microscopy (TEM) in a heavily-deformed Ti-45 Al-10Nb-2.5Mn (at.%) alloy. The deformation twins become severely bent afte r blocking numerous matrix dislocations. The (111)(DT) plane in the twins e xhibits a misorientation angle with the (111)(M) plane in the matrix, and n umerous 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 i ntersections show different tilting directions due to different orientation s 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 d irection could induce the formation of small-angle tilting grain boundaries in the intersection area of the type-I. The opposite propagation of severa l incident twin tips could induce a triangular striated region near the int ersection area. Some nanotwins nucleate and propagate with a homogeneous tw inning shear mechanism, and were limited mostly in the triangular striated region. (C) 2001 Elsevier Science B.V. All rights reserved.