Analysis of texture evolution and slip activity of a near-α titanium alloy sheet under different biaxial-tension strain paths

Abstract

Understanding of the texture evolution and slip activity of titanium alloys during hot forming is crucial for designing reasonable strain path and improving formability of materials. To this goal, a hot gas bulging test was developed to investigate the texture evolution and slip activity of a near-α TA32 titanium alloy sheet under different biaxial-tension strain paths at elevated temperature. Four elliptical through-hole dies with different minor–major axis ratios and two dies with different suddenly-changed cavities were designed to realize various strain paths. The deformation texture was characterized by electron backscatter diffraction (EBSD) technique. The global Schmid factor (GSF) was adopted to analyze the dominant slip systems under different strain paths and their effects on texture evolution. Results showed that when the strain path changed from equi-biaxial tension to plane strain, the formability of the material decreased due to the decrease of the prismatic slip activity of the initial transverse texture. Meanwhile, the deformation texture changed from a band with (0001) orientation perpendicular to RD to TD-split basal bimodal texture. Furthermore, nonlinear strain paths at elevated temperature can be effectively realized by bulging with cavities suddenly-changed dies. When the first principal stress direction was converted from TD to RD during continuous deformation, the activity of pyramidal-2 slip obviously increased, and the preference of (0001) orientation transformed from perpendicular to RD into rotation towards RD. The formability of titanium alloy sheets during hot deformation can be improved by controlling texture based on the relationship between strain paths, texture evolution and slip activity.

Keywords

• Near-α TA32 sheet
• Strain path
• Texture evolution
• Slip activity
• Hot gas bulging test