Tens ion-compression asymmetry in yielding and strain hardening behavior of CP-Ti at room temperature

The tension-compression asymmetry including the yielding and strain hardening asymmetry of a commercially pure titanium (CP-Ti) at room temperature was studied using uniaxial tensile and compressive tests. The deformation twinning modes responsible for the tension-compression asymmetry were analyzed using the electron back scattered diffraction technology. The CP-Ti exhibits a strong tension-compression asymmetry in yielding and strain hardening. The prismatic slip is the most easiest to activate either for tension or compression. The deformation twinning mode can be characterized by the secondary {1012} twin variants in primary {1122} twins for tension and the secondary {1172} twin variants in primary {1012} twins for compression. The secondary twin variants are the dominated twinning modes whether for tension or compression, determining the final yielding behavior of the titanium. The stress required to activate the secondary extension twins in tension is larger than that to activate the secondary contraction twins in compression, leading to the tension-compression asymmetry in yielding. The strain hardening enhancement of the CP-Ti is a result of the combination of the Hall-Petch hardening by grain refinement and texture hardening by lattice re-orientation both resulting from the deformation twinning. The stronger effect of these two hardening mechanisms on compression than on tension leads to the tension-compression asymmetry in strain hardening.