Strength enhancement of a biomedical titanium alloy through a modified accumulative roll bonding technique

The strength of a biomedical ββ-type alloy, Ti–25Nb–3Zr–3Mo–2Sn, was enhanced through severe plastic deformation using a modified accumulative roll bonding technique. Incremental strength increases were observed after each cycle, while ductility initially fell but showed some recovery with further cycles. After 4 cycles there was a 70% improvement in the ultimate tensile strength to 1220 MPa, a two-fold increase in the 0.5% proof stress to 946 MPa and the ductility was 4.5%. The microstructure comprised of ultrafine grain ββ grains heavily elongated in the rolling direction with a fine dispersion of nanocrystalline αα phase precipitates on the ββ grain boundaries. Shear bands formed in order to accommodate large plastic strains during processing and the grains within the bands were significantly finer than the surrounding matrix.

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► A modified accumulative roll bonding process was developed.
► A microstructure composed of ultrafine ββ grains and nanocrystalline αα precipitates developed.
► The strength of the alloy was increased two-fold.
► Significant recovery of ductility occurred during the processing.
► A broad distribution of grain sizes in conjunction with a dense shear band network formed.