Recent technological advances have revolutionized biomedical industry including orthopedic implants of Ti alloys characterized by Low Young’s Modulus (E). Former researches in the field have shown that the alloys must prevent stress shielding arising from a difference in Low Young’s modulus between Ti alloys implant which is widely used for orthopedic implants including artificial hip-joint stems and cortical bone. Moreover, researchers have of late established that the least stable β Ti alloys exhibit low E values, which can be interpreted in terms of both lattice softening near Ms (Martensitic transformation starting temperature) and suppression of formation of an athermal ω phase with a high elastic modulus. Actually, the addition of Sn to Ti- Nb alloys has been shown to play a major role in stabilizing the β phase and suppressing the formation of the athermal ω phase. To this end, Ti, Nb and Sn are considered highly suitable constituent elements for biomaterials, such as; bone plates, artificial ligaments and tendons, blood vessels prosthese, bone cement and dental implants for tooth fixation.
Precisely, the Low Young’s Modulus of the least stable β Ti-Nb-Sn alloys is obtained during rolling where α” martensite induces in the least stable β Ti alloys. In this regard, the result has shown that the Young’s modulus of α” martensite exhibits anisotropic, elastic behavior and that the Young’s modulus of the least stable β Ti alloys decreases owing to the development of the favorable α” texture during rolling. However, in the previous researches, almost no attention has been paid to the texturing in the deformation induced α” martensite in the parent β phase. Unfortunately, previous studies have demonstrated that the Young’s modulus of body centered cubic (bcc) single crystals of β Ti–Nb–based alloys depend significantly on the crystal’s orientation in order of appearance. On this account, Tohoku University researchers: Professor Shuji Hanada, Professor Naoya Masahashi, Dr. Satoshi Semboshi, Dr. Taek Kyun Jung, developed a new and novel approach to assess the effects of composition and cold groove-rolling on Young’s modulus. Their goal was to achieve low Young’s modulus in β Ti-Nb-Sn ternary alloys. Their work is currently published in research journal, Materials Science & Engineering A.
In their analogy, they focused on assessing the effects of reduction of Young’s modulus and tensile strength of the alloys. Remarkably, the authors posted promising results whereby Young’s modulus was seen to decrease with increasing Sn content. In their approach, the Young’s modulus of alloys in the α” region was first reduced by cold groove–rolling. As a consequence, there was a reduction of Young modulus in the β(ꭃ)+α” alloys region due to reorientation of deformation–induced α” variants during rolling.
The researchers established that the instability of the β phase it’s evident that the magnitude of the elastic Modulus in metallic body is closely connected to the martensitic transformation. Overall, the researchers were able to validated the fact that an orthorhombic α” phase in a β phase behaves like body centered cubic phase during deformation whereby several groove–rolled β Ti–Nb–Sn alloys rods form textures along the rolling direction.
In summary, the study presented a novel approach developed with the aim of improving elasticity of β Ti-Nb-Sn alloys so as to facilitate orthopedic applications. In this respect, the β phase was stabilized by the addition of Sn. Consequently, the low Young’s Modulus of quenched alloys was controlled by the stability of the β phase and the ease of (ꭃ) formation which depends on alloy composition. In a statement to Advances in Engineering, Professor Shuji Hanada explained that the constituent phase of quenched and rolled alloys were classified into three regions of β, β(ꭃ)+α” and α” in the Ti-Nb-Sn ternary phase, based on their approach.
Professor Hanada commented “we found that the least stable b Ti-Nb-Sn alloys quenched from high temperature (ST) show considerably low Young’s modulus of 50~55 GPa. Then, to further decrease Young’s modulus, groove-rolling texture was utilized, because Young’s modulus is sensitive to crystal orientation. The groove-rolling of the least stable b Ti-Nb-Sn alloys (CGR) developed extremely sharp preferred orientations of a” and b along the rolling direction (Figure 1), yielding Young’s modulus less than 50 GPa. Especially, the lowest Young’s modulus of 36 GPa, which is close to human cortical bone, is attained in the groove-rolled Ti-35Nb-3.75Sn. This value is much lower than that of Ti-6Al-4V, which is widely used as orthopedic implants (Figure 2). The groove-rolling is effective in reducing Young’s modulus by texturing along the rolling direction and moreover it is expected that the alloy is strengthened by work hardening.
He added “This paper points out that the large lattice deformation strain along a” ∥ b on deformation-induced a” martensitic transformation is responsible for the low Young’s modulus along the rolling direction.”
S. Hanada, N. Masahashi, T.K. Jung, S. Semboshi. Low Young’s Modulus of cold groove-rolled b Ti–Nb–Sn alloys for orthopedic applications. Materials Science & Engineering A 802 (2021) 140645.