Low Young's modulus of cold groove-rolled β Ti-Nb-Sn alloys for orthopedic applications

초록

The effects of composition and cold groove-rolling on Young's modulus were investigated to achieve low Young's modulus in beta Ti-Nb-Sn ternary alloys for orthopedic applications, using Ti-(27.5-37.5)%Nb-(2.5-11.25)%Sn ternary alloys. Optical microscopy, transmission electron microscopy, and X-ray diffractometry revealed that the constituent phases of quenched and rolled alloys were classified into three regions of beta, beta(omega)+alpha" and alpha" in the Ti-Nb-Sn ternary phase diagram. The beta phase was observed to stabilize by the addition of Sn, and the least stable beta alloys existed along a line connecting Ti-37.5Nb-2.5Sn and Ti-27.5Nb-11Sn. Low Young's moduli of approximately 50 GPa were achieved by the least stable, quenched beta Ti-Nb-Sn alloys, and these further decreased by cold groove-rolling, reducing the cross section by 75%. The lowest Young's modulus of 36 GPa was realized for the cold groove-rolled Ti-35Nb-3.75Sn alloy, in which the textures of [010]alpha" of deformation-induced alpha" martensite and [011]beta of the beta matrix developed preferentially, parallel to the rolling direction. The lattice deformation strain along the [010]alpha" axis accompanied by beta to alpha" martensitic transformation was observed to depend on the alloy composition and was maximized in Ti-35Nb-3.75Sn. Thus, the low Young's modulus of the least stable beta Ti-Nb-Sn alloys obtained after cold groove-rolling was attributed to the development of [010]alpha" and [011]beta textures along the rolling direction, and the lowest Young's modulus of the cold groove-rolled Ti-35Nb-3.75Sn alloy was due to a large lattice deformation strain along the [010]alpha" axis accompanied by beta to alpha" transformation.

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