Study of {112̄1} Twinning in α-Ti by EBSD and Laue Microdiffraction

Abstract

Activity of the {112̄1} {1̄1̄11} extension twinning (T2) mode was analyzed in a commercial purity Ti sample after 2 pct tensile strain imposed by four-point bending. The sample had a moderate c-axis fiber texture parallel to the tensile axis. Compared with the many 101̄2} {1̄011} extension (T1) twins that formed in 6 pct of the grains, T2 twins were identified in 0.25 pct of the grains by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) maps. Most of the T2 twins exhibited irregular twin boundaries (TBs) on one side of the twin. High-resolution EBSD revealed both intermediate orientations at some matrix/twin interfaces and substantial lattice rotation within some T2 twins. Interactions between matrix 〈c +a〉 dislocations 1/3〈12̄13〉and a {112̄1} T2 twin were investigated by combining SEM/EBSD slip trace characterization and Laue microdiffraction peak streak analysis. 〈c+-rfaut〉 dislocations that originally glided on a pyramidal plane in the matrix were found on other planes in both the matrix and the twin, which was attributed to extensive cross-slip of the screw component, whose Burgers vector was parallel to the twinning plane. On the other hand, thickening of the twin could engulf some pile-up edge components in front of the TB. During this process, these 〈c+-rfaut〉 dislocations transmuted from a pyramidal plane (01̄11) in the matrix to a prismatic plane (1̄010)T in the twin lattice. Finally, possible mechanisms for the nucleation and growth of T2 twins will be discussed. © 2013 The Minerals, Metals & Materials Society and ASM International.