Abstract
A Ti-6Al-7Nb alloy with three different initial microstructures was processed by high-pressure torsion (HPT) and the resultant microstructure and mechanical properties of the alloy after HPT processing were investigated. The microstructure of the as-received alloy was an equiaxed (α+β) microstructure. The rods were subjected to solution treatment and aging (STA) treatment to obtain a bi-modal microstructure consisting of an equiaxed α phase and lamellar α+β phases, and those to solution treatment and quenching (STQ) treatment to obtain a bi-modal microstructure consisting of equiaxed α-phase and acicular α’-phase. Disks were cut from those rods and were processed by HPT under a pressure of 6 GPa. After HPT processing through 20 revolutions, the alloy with each of the three initial microstructures showed ultrafine grains with a size of ~70 nm. The alloy resulted in a higher tensile strength (1350 MPa) in both the bi-modal microstructures than that (1250 MPa) in the alloy with equiaxed α+β microstructure after HPT processing. It was shown that the Ti-6Al-7Nb alloy with the bi-modal microstructure was strengthened more than with the equiaxed α+β microstructure when the alloy was processed by HPT. Furthermore, the alloy with bi-modal microstructure consisting of equiaxed α-phase and acicular α’-phase showed a good balance between the tensile strength (1280 MPa) and the elongation to fracture (22%) after HPT processing through 1 revolution. In summary, therefore, large strength and elongation of the Ti-6Al-7Nb alloy were simultaneously achieved by HPT processing.
Highlights
A Ti-6Al-7Nb alloy is widely used in medicine, such as artificial hip joints, spinal fixators, and dental implants, due to its lightweight and superior corrosion resistance
Our previous study showed that the grain refinement of the Ti-6Al-7Nb alloy with equiaxed microstructure was achieved by High-pressure torsion (HPT) processing [5] and the grain-refined Ti-6Al-7Nb alloy had a good cytocompatibility as with the alloy before HPT processing [6]
A Ti-6Al-7Nb alloy with three different initial microstructures was processed by HPT processing and the resultant microstructure and mechanical properties after HPT processing were investigated
Summary
A Ti-6Al-7Nb alloy is widely used in medicine, such as artificial hip joints, spinal fixators, and dental implants, due to its lightweight and superior corrosion resistance. This alloy can be an excellent alternative of the more widely used Ti-6Al-4V alloy, because vanadium shows cytotoxicity. These alloys have a bi-modal microstructure consisting of α and β phases, which result in good balance of mechanical properties for medical applications. For Ti-6Al-7Nb alloy, it was reported that the ultra-fine grained microstructure can be produced by HPT [3,4], but the mechanical properties after HPT are not well investigated. The Ti-6Al-7Nb alloy with three different initial microstructures were processed by HPT and the resultant microstructure and mechanical properties were investigated
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