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Abstract:
The presented work is devoted to experimental studies of the energy storage process in the tensile test of the ultrafine-grained (UFG) titanium in comparison with the coarse-grained one. The UFG titanium was obtained using severe plastic deformation method (SPD) called twist extrusion (TE) that is briefly presented.
The experiments were performed on three groups of titanium specimens. Two of them (T1 and T2) were cut from the materials obtained by TE method. The T1 titanium was processed by 4 passes through the left twist die, whereas for the T2 titanium the twist direction was changed after the first pass. The last group (T0) was prepared from the annealed sheet of coarse-grained titanium. It was noticed that mechanical properties of the material underwent TE differs considerably from properties of te coarsed-grained one. It was observed that yield point obtained for specimens after TE is about 30% higher then that for coarsed-grained material. However, the elongation decrease was observed for both groups of specimens after TE (T1~60%, T2~25%) with respect to T0 ones.
The energy storage investigations show the differences in the energy storage rate for T1 and T2 specimens. In the case of T1 specimens the energy storage rate decreases rapidly with strain whereas for T2 specimens (where twist direction was changed) the energy storage rate remains constant at the homogeneous deformation range. The experimental results show that the change of the twist direction during TE may improve the mechanical properties of the material. The constant rate of energy storage in specimens after twist direction change may be macroscopic manifestation of homogeneous and more stable structure of the material.

Keywords:
energy storage rate, ultrafine-grained titanium, severe plastic deformation, twist extrusion