Numerical prediction of [formula omitted] compression twin activation in commercially pure titanium under uniaxial tension

Abstract

In this study, the criteria for {112‾2} compression twinning in commercially pure titanium (CP–Ti) were investigated by uniaxial tensile tests, crystal plasticity finite element (CPFE) analyses, and slip operation factor (SOF) calculations. First, the aggregates of the [0001] axes of CP-Ti were inclined in the rolling direction (RD), implying its RD-split texture. The development of the crystal orientation distribution with deformation was observed by electron back-scattered diffraction (EBSD). Active slip systems were identified by kernel average misorientation (KAM) and intergranular misorientation axis (IGMA) analyses. The dominant slip system was prismatic <a>, whereas the non-prismatic <a> slip systems were activated near the grain boundary. Active twin systems were also identified by the rotation angles of the [0001] axes between the twin and matrix. The dominant active twin system was the {112‾2} compression twin, although a uniaxial tensile load was applied. Second, the positions of {112‾2} twinning were predicted by CPFE analysis using the resolved shear stress (RSS) criterion while considering plastic deformation. SOF analysis was also employed for the prediction. The CPFE and SOF analyses yielded almost the same level of prediction accuracy. However, these calculations do not completely predict the twinning positions. Finally, the criteria for {112‾2} twinning were discussed, and it was revealed that hydrostatic pressure and RSS are possible criteria for {112‾2} twinning in the continuum model.