Phase transformations in a heterogeneous Ti-xNb-7Zr-0.8O alloy prepared by a field-assisted sintering technique

Tailoring a Low Young Modulus for a Beta Titanium Alloy by Combining Severe Plastic Deformation with Solution Treatment

“…There have been some progress in this direction: while conventionally/commonly used αor (α + β)-Ti alloys (including consecrated Ti-6Al-4V) exhibit a modulus of about 100-110 GPa, β-Ti alloys exhibit moduli of around 55-70 GPa [15][16][17][18][19][20], which is much closer to the elastic modulus of cortical bone (approximately 30 GPa) [21]. Associated with the Young's modulus should be a sufficiently high yield strength, which, for the β-Ti alloy, seems to be quite a difficult requirement as the yield strength generally has medium values for the β-single microstructure [6].…”

“…Aside from the β-stabilizing character, the biocompatibility function of these elements is very important in addition to that of titanium. From this perspective, Nb, Zr, and Ta are considered able to be used without limit due to their non-cytotoxicity character [6,7]. On the other hand, Mo and Fe can be used to a limited extent [6,8,9].…”

“…From this perspective, Nb, Zr, and Ta are considered able to be used without limit due to their non-cytotoxicity character [6,7]. On the other hand, Mo and Fe can be used to a limited extent [6,8,9]. The most appreciated is Nb, which also has the strongest β-stabilizing character and high biocompatibility [1,2,10].…”

“…From this point of view, Fe is a good alternative being more accessible [8][9][10][11]. Therefore, many studies have tried to replace expensive Ta with Fe also considering that Ta has a very high melting temperature (T top Ta = 2996 • C) comparative to the above enumerated, making the alloy synthesis and homogenization difficult [6,8,9,11,12]. The next demanding condition for the β-Ti alloy design refers to obtaining the minimum possible elastic modulus to avoid the so-named "stress shielding effect".…”

“…The second modality explored to meet the above requirements for β-Ti alloys used for implants is to introduce oxygen alongside the alloying elements. Here, however, some uncertainties regarding the influence degree of two dichotomous manifestations of the oxygen still persists: on one hand, oxygen is considered a α-stabilizing element with respect to the β-transus temperature, which increases with oxygen addition [32]; on the other hand, the β-stabilizing nature of oxygen is more often taken into account and reported on considering its strong interstitial strengthening character [4][5][6] that can thus inhibit stress-induced martensitic transformation (β→α") [33][34][35][36]. It seems that the first manifestation is less influential than the second one if a sufficiently high content of β stabilizing elements is taken into account, since the reports on the second direction of manifestation are more numerous [7,11,[33][34][35][36][37][38].…”