Superplastic and Severe Plastic Deformation in Titanium Alloys

Titanium alloys are prized for their high specific strength, corrosion resistance and biocompatibility, yet their formability at room temperature is limited by the strong hexagonal close-packed crystal structure of α‐phase and the limited slip systems it offers. Superplasticity—where alloys exhibit extremely large uniform elongations at elevated temperatures—has been exploited in Ti–6Al–4V and related alloys via grain boundary sliding and accompanying dislocation-based accommodation, enabling the fabrication of complex shapes by superplastic forming. Complementary to superplastic forming, severe plastic deformation (SPD) techniques such as equal channel angular pressing, high-pressure torsion, calibre-rolling and multidirectional swaging impose very large strains to refine the microstructure to the ultrafine or nanometre scale. This grain refinement imparts a substantial strength increase via the Hall–Petch effect, while careful control of thermal treatments preserves ductility and thermal stability. Practical applications range from net-shape aero-engine components and biomedical implants to energy-sector structural parts. The key challenges lie in controlling deformation textures to mitigate anisotropy, ensuring microstructural stability during service, and scaling SPD processes for industrial production without compromising the advantageous strength–ductility–stability synergy.

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Superplastic and Severe Plastic Deformation in Titanium Alloys publication trend

The graph below shows the total number of articles in superplastic and severe plastic deformation in titanium alloys across all publications each year (not limited to Nature Index journals).

Technical terms

Superplasticity: The capacity of a polycrystalline material to sustain very large uniform elongations—often exceeding 400%—under tensile loading at elevated temperatures by grain boundary sliding and compatible accommodation mechanisms.

Severe plastic deformation (SPD): A group of processing methods that impose very large strains on a bulk material to refine its grains to the ultrafine or nanometre scale without altering its overall dimensions.

Grain boundary sliding: The relative displacement of adjacent grains along their boundaries, which accommodates plastic deformation during superplastic flow.

Equal channel angular pressing (ECAP): An SPD technique where a billet is extruded through an intersecting‐channel die of identical cross section, imposing intense shear deformation while retaining the billet’s geometry.

Ultrafine-grained microstructure (UFG): A grain structure in which the mean grain size is below 1 µm, achieved by SPD, which enhances strength through grain boundary strengthening while maintaining reasonable ductility.

References

1. Texture, elastic anisotropy and thermal stability of commercially pure titanium prepared by room temperature ECAP. Materials & Design (2023).
2. On the mechanisms of superplasticity in Ti–6Al–4V. Acta Materialia (2016).
3. Manufacturing Ultrafine-Grained Ti-6Al-4V Bulk Rod Using Multi-Pass Caliber-Rolling. Metals (2015).