Revealing abnormal {11-21} twins in commercial purity Ti subjected to split Hopkinson pressure bar

Abstract

The deformation behavior of Ti alloys during conventional deformation, such as rolling and compression,have been extensively investigated, while it is less understood during high strain rate deformation. In thepresent work, a commercial purity (CP) Ti alloy was subjected to high strain rate (~600 s 1) compressiondeformation using a split Hopkinson pressure bar (SHPB) system. By multi-impacts, an accumulativedeformation strain of ~0.15 was achieved. The microstructural evolution has been systematicallyanalyzed by electron backscatter diffraction (EBSD). It is found that the CP-Ti alloy has been deformedpredominantly by three different twinning modes, {1012} (T1), {1121} (T2) and {1122} (C1). A largefraction of the {1121} (T2) twin boundary (TB) segments are found to be in connection with deformationband (DB) boundary segments with misorientation angles much lower than the theoretical value of the{1121} (T2) TB, ~35. Based on the analysis of the crystallographic nature of these abnormal {1121} (T2)TBs and the calculation of Schmid factor, it is suggested that these abnormal {1121} (T2) TBs are evolvedfrom DB boundaries through the accumulative slip of single basal-⟨a⟩dislocations, namely a kinkingmechanism. This special twinning mode of the {1121} (T2) twin has been attributed to the high strainrate deformation during SHPB compression, which is helpful for understanding the deformation andtwinning behavior during high strain rate deformation.