Microscopic strain localisation in Ti-6Al-4V during uniaxial tensile loading

The titanium alloy Ti-6Al-4V is investigated in terms of the effect of macrozones within the microstructure through cross correlation of local strain measurements and microstructure, using digital image correlation (DIC) and electron backscatter diffraction (EBSD) techniques. Three different product forms of Ti-6Al-4V including strong-, intermediate- and a no-macrozone condition with a weak texture have been investigated focusing on the impact of the primary macrozone orientation, macrozone dimensions and loading direction. Strain localisation was characterised at the microscale using optical microscopy during in-situ uniaxial tensile loading and analysing the recorded images using digital image correlation. The no-macrozone material and the strong-macrozone condition loaded parallel to the macrozones exhibited homogeneous strain behaviour in both the elastic and plastic strain regions. The strong (soft-orientated) macrozone condition loaded at 45° and 90° both exhibited heterogeneous strain behaviour in grains with their c-axis oriented perpendicular to the loading direction, while the intermediate (hard-oriented) macrozone material exhibited heterogeneous strain behaviour when the majority of grains had their c-axis parallel to the loading direction. The strong-macrozone material showed a direct correlation between macrozones with their grains favourably oriented for prismatic slip and high strain regions when loaded at 45° to the elongation direction. Correlating a region of high strain localisation with Schmid factor maps for basal and prismatic slip, suggests a likelihood of basal slip when loading at 90°.