Revealing abnormal {11[formula omitted]1} 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 the present work, a commercial purity (CP) Ti alloy was subjected to high strain rate (∼600 s−1) compression deformation using a split Hopkinson pressure bar (SHPB) system. By multi-impacts, an accumulative deformation strain of ∼0.15 was achieved. The microstructural evolution has been systematically analyzed by electron backscatter diffraction (EBSD). It is found that the CP-Ti alloy has been deformed predominantly by three different twinning modes, {101¯2} (T1), {112¯1} (T2) and {112¯2} (C1). A large fraction of the {112¯1} (T2) twin boundary (TB) segments are found to be in connection with deformation band (DB) boundary segments with misorientation angles much lower than the theoretical value of the {112¯1} (T2) TB, ∼35°. Based on the analysis of the crystallographic nature of these abnormal {112¯1} (T2) TBs and the calculation of Schmid factor, it is suggested that these abnormal {112¯1} (T2) TBs are evolved from DB boundaries through the accumulative slip of single basal-〈a〉 dislocations, namely a kinking mechanism. This special twinning mode of the {112¯1} (T2) twin has been attributed to the high strain rate deformation during SHPB compression, which is helpful for understanding the deformation and twinning behavior during high strain rate deformation.