Structural refinement of titanium-aluminum-niobium alloy for biomedical applications

In this work, a modification of the microstructure of a commercial Ti-6Al-7Nb alloy was accomplished by high-pressure torsion (HPT) at room temperature, to produce a bulk nanostructure on discs of 10 mm diameter and ∼0.8 mm thickness. The metallographic analyses of the discs were performed by optical microscopy and scanning electron microscopy with energy dispersive spectroscopy. The results confirmed the presence of aluminum (Al) and niobium (Nb) as the sole alloying elements, promoting a duplex (α + β) titanium (Ti) microstructure prior to HPT processing. After HPT processing, nanostructure refinement was attained, reflected in the X-ray diffraction profiles as broadening of the α-Ti and β-Ti peaks and the appearance of the ω-Ti phase. Transmission electron microscopy confirmed a grain size < 100 nm after HPT processing for N = 5 revolutions. Microhardness increased significantly with straining by HPT, which can be attributed both to the grain refinement and the formation of the ω-Ti phase.