The occurrence of ideal plastic state in CP titanium processed by twist extrusion

This paper deals with the analysis of strength and plastic characteristics of commercially pure (CP) titanium as a function of equivalent plastic strain accumulated during Twist Extrusion (TE) process. It is shown experimentally that multipass TE leads to the saturation of the following characteristics of the material: yield stress, reduction in area, elongation to failure, and uniform elongation. This fact indicates the occurrence of an ideal plastic state in the processed material. The threshold value of accumulated plastic strain for ideal plastic behavior of CP titanium during TE is defined. The strain state and mechanical properties of CP titanium billets processed by TE are studied. An explanation for the hardening on the axis of a billet during TE is offered. The analysis of deformation modes on the billet axis during TE and High Pressure Torsion is carried out. It is shown that the differences in strain state on the axis are caused by the difference in symmetry of these processes.