Formation of {11(2)over-bar1} twin boundaries in titanium by kinking mechanism through accumulative dislocation slip

The twinning behavior and kinking behavior of a commercial purity Ti subjected to room temperature dynamic plastic deformation (DPD) has been studied. Three types of deformation twins, {10 (1) over bar2}, {11 (2) over bar2} and {11 (2) over bar1}, have been observed. It is found that a considerable fraction of the {11 (2) over bar1} twin crystals were encompassed by the twin boundary segments in connection with kink band boundaries with much lower misorientation angles. A close investigation on the crystallographic nature of these deformation twins revealed that the {11 (2) over bar1} twin boundaries have evolved from deformation kink band boundaries through accumulative slip of single basal-< a > dislocations. This mechanism for the formation of twin boundaries is different from the known mechanisms through deformation twinning in metals, for which the twin orientation relationship has been achieved once the twin embryo is nucleated. The mechanism for the formation of kink band, the transformation from kink band boundary to deformation twin boundary and the further evolution of twin boundaries during DPD have been discussed in terms of Schmid factors of various dislocation slip systems. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.