Schmid factor analysis of twinning behavior in Ti–2Al alloy

The Schmid factors (SFs) of grains in a Ti–2Al (mass%) alloy deformed by quasi-static compression at room and elevated temperatures were determined by electron backscattering diffraction and presented in a SF map created based on theoretical calculation in a spherical coordinate system. These data were applied to investigate the twinning behavior in the alloy during its deformation at different temperatures. It was found that mainly {101‾2} twinning occurred in the deformed samples, and the fraction of twinned grains decreased with increasing deformation temperature. Based on the calculated SF distribution maps of twined and untwined grains in the specimens deformed at different temperatures, the critical SFs required to activate {101‾2} twinning in them were determined. From the critical SFs and associated flow stress, the corresponding critical resolved shear stress was calculated, and found to decrease linearly with the increase of deformation temperature from 140 MPa at room temperature to 50 MPa at 800 °C. The macroscopic thermal softening coefficient, m, of the Ti–2Al alloy was also studied, and it was found that the 2mass%Al addition to Ti did not cause any significant change. On the other hand, the strain hardening behavior of the alloy was dictated by the amount of twinning during the deformation process.