Achieving high strength and low elastic modulus in interstitial biomedical Ti–Nb–Zr–O alloys through compositional optimization

Abstract

High strength and low elastic modulus are critical properties of biomedical titanium alloys for manufacturing of load-bearing orthopaedic implants. Single phase beta Ti alloys can achieve low elastic modulus, but their strength is usually not high enough. Conversely, commonly used strengthening by alpha phase precipitation causes a sharp increase of elastic modulus. This paper presents an approach for achieving both high strength and low elastic modulus by tailoring the alloy composition. High strength is achieved by controlled alloying with oxygen, which causes interstitial strengthening. Solid solution strengthening by Ta, which is often used in biomedical Ti alloys then becomes redundant. Low modulus is achieved due to premartensitic softening by tailoring the content of beta stabilizing elements – the stability of beta matrix is reduced due to the proximity to the martensitic transformation. Using this approach we obtained a compositionally optimized Ti–29Nb–7Zr-0.7O alloy, with yield stress exceeding 1000 MPa and elastic modulus of 65 GPa. High strength, low elastic modulus and good ductility are achieved by simple alloying without any additional special treatment. Ti–29Nb–7Zr-0.7O alloy appears promising for manufacturing of load bearing implants.