During the last decade it has been shown that severe plastic deformation (SPD) is a very
effective for obtaining ultra-fine grained (UFG) and nanostructured materials. The basic SPD
methods are High Pressure Torsion (HPT) and Equal Channel Angular Extrusion (ECAE).
Recently several new methods have been developed: 3D deformation, Accumulative Roll Bonding,
Constrained Groove Pressing, Repetitive Corrugation and Straightening, Twist Extrusion (TE), etc.
In this paper the twist extrusion method is analyzed in terms of SPD processing and the essential
features from the “scientific” and “technological” viewpoint are compared with other SPD
techniques. Results for commercial, 99.9 wt.% purity, copper processed by TE are reported to show
the effectiveness of the method. UFG structure with an average grain size of ~0.3 μm was
produced in Cu billets by TE processing. The mechanical properties in copper billets are near their
saturation after two TE passes through a 60º die. Subsequent processing improves homogeneity
and eliminates anisotropy. The homogeneity of strength for Cu after TE is lower than after ECAE
by route BC, but higher than after ECAE by route C. The homogeneity in ductility characteristics
was of almost of inverse character. The comparison of mechanical properties inhomogeneity in Cu
after TE and ECAE suggests that alternate processing by ECAE and TE should give the most
uniform properties.
This paper investigates microstructures and mechanical properties of the TI-6AL-4V ELI alloy processed by ECAP and extrusion with various morphology of α and β-phase. Preliminary thermal treatment consisted of quenching and further high-temperature ageing. The present work reveals that the decrease of volume fraction of α-phase globular component in the initial billet results in a more homogeneous structure refinement during SPD, lower internal stress, enhancement of microstructure stability and mechanical properties. An ultimate strength of UTS ≥1350 MPa was obtained in the Ti-6Al-4V ELI alloy while maintaining a ductility of δ≥11%.
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