Origin of ultralow Young׳s modulus in a metastable β-type Ti–33Nb–4Sn alloy

Abstract

Although there is difficulty in growing a Ti-33Nb-4Sn single crystal due to its ultralow β-phase stability, the single-crystal elastic constants of metastable β-type Ti-33Nb-4Sn (wt%) alloy were extracted successfully from its polycrystal by in-situ synchrotron X-ray diffraction technique, to clarify the origin of the ultralow Young's modulus in its polycrystal. It is indicated that compared to binary TiCr, TiV and TiNb alloys, the Ti-33Nb-4Sn alloy possesses slightly lower β-phase stability with respect to {110}<110>(-)shear (i.e., C׳) but much lower β-phase stability regarding to {001}〈100〉 shear (i.e., C44). An analysis by the Hill approximation suggests that the ultralow isotropic polycrystalline Young׳s modulus (EH) of Ti-33Nb-4Sn alloy originates from the extremely low shear modulus C44 as well as the relatively low C׳. This indicates that in addition to C׳, C44 has a significant contribution to the Young's modulus of polycrystal, which challenges a conventional understanding that the Young's modulus of β-type Ti alloys is predominantly determined by C׳.

In situ synchrotron X-ray diffraction study of deformation behaviour of a metastable β-type Ti-33Nb-4Sn alloy

“…Further investigation shows that this ultralow modulus is closely associated with its low β-phase stability with respect to α" martensitic transformation [30]. It is also shown that the Ti-33Nb-4Sn alloy exhibits multiple deformation behavior, involving "double yielding", nonlinear deformation and conventional linear elastic deformation, under different thermo-mechanical treatment conditions [29,30].…”

“…Further investigation shows that this ultralow modulus is closely associated with its low β-phase stability with respect to α" martensitic transformation [30]. It is also shown that the Ti-33Nb-4Sn alloy exhibits multiple deformation behavior, involving "double yielding", nonlinear deformation and conventional linear elastic deformation, under different thermo-mechanical treatment conditions [29,30]. However, the deformation behaviour of the Ti-33Nb-4Sn alloy, especially its correlation with SIM transformation, has not yet been investigated detailedly, although an in-depth understanding of this issue might help to establish theoretical foundations for designing novel biomedical Ti alloys with ultralow elastic modulus.…”

Mechanical properties, corrosion behaviour and biocompatibility of TiNbTaSn for dentistry

“…However, the alloys may suffer from biomechanical incompatibility. There is a difference between the elastic modulus of the material (ca 105 GPa) and the modulus of bone (16)(17)(18)(19)(20)(21)(22)(23)(24)(25) GPa for cortical and 1-4 GPa for trabecular bone) [3]. This difference may cause the loss of mechanical bond because the regeneration of the bone tissue is probably controlled via mechanical stimulation of osteocytes [4][5][6].…”

“…This structure reduces tensile strength, fatigue strength and hardness [19][20][21]. However, the presence of alpha and omega phases can be suppressed by tin alloying, and the Young moduli of these alloys are about 40 GPa [16,[22][23][24][25][26]. Tin and other elements, such as Nb and Ta, also improve the corrosion resistance by enriching the passive layer by stable and non-toxic oxides such as Nb 2 O 5 , Ta 2 O 5 , and SnO 2 [16,[27][28][29][30].…”

In situ synchrotron X-ray diffraction study of stress-induced martensitic transformation in a metastable β-type Ti-33Nb-4Sn alloy

“…It was also reported that the ultralow modulus of Ti-33Nb-4Sn (wt. %) alloy is closely related to its low β-phase stability with respect to α" martensitic transformation [13]. However, the martensitic transformation behaviour in the Ti-33Nb-4Sn alloy has not yet been clarified in detail, although an in-depth understanding of this issue may provide help in establishing foundations for developing new Ti alloys, such as biomedical Ti alloy with ultralow elastic modulus.…”