Ti-Nb-Sn alloys with bone-like elastic modulus and superelasticity

Low elastic modulus, superelasticity and non-toxicity are required for implant materials for curing bone disease. In this study, non-toxic superelastic Ti-15Nb-(4-6)Sn (at%) shape memory alloys were developed to achieve the bone-like elastic modulus for biomedical applications by varying Sn content to adjust the factors such as transformation temperature, valence electron density, the amount of ω phase and texture component which are well known to affect the superelasticity and elastic modulus of titanium alloys. The elastic modulus of 68.8 GPa in the 4Sn specimen decreased to 41.5 GPa in the 5Sn specimen due to the suppression of α" martensite and the decrease in the amount of athermal ω (ω_ath) phase. A good combination of low elastic modulus (31.5 GPa) and room temperature superelasticity with recovery strain of 2.1 % was obtained in the 5.5Sn specimen. In this specimen, (110)_β[001]_β (Goss texture) was developed as the dominant texture component and the ω_ath phase was completely suppressed. More detailly, along the rolling direction (RD), the [001]_β//RD texture which effectively reduces elastic modulus along the RD was formed in 5Sn and 5.5Sn specimens and its intensity increased largely in the 5.5Sn specimen. Such a bone-like elastic modulus is attributed to the formation of a strong [001]_β//RD texture as well as the absence of the ω_ath phase in β matrix and α" martensite.