Thermo Mechanical Working and Heat Treatment Studies on Meta-Stable Beta Titanium Alloy (Ti15V3Al3Sn3Cr) Plates

Abstract

The beta titanium alloys are highly cold workable in annealed condition, due to presence of single phase bcc structure (beta) at ambient temperature. The Ti15V3Al3Sn3Cr alloy is a metastable beta alloy retains single beta phase at ambient temperature by beta annealing. The beta alloys are most hardenable among titanium alloys, due to the formation of hard alpha (hcp) precipitates in beta (bcc) grains in solution treated and aged (STA) conditions. The present paper brings out the hot forging and rolling studies carried above beta transus temperature and correlating microstructure with mechanical properties in heat treated conditions (a. 800°C for 30 minutes and b. 800°C for 45 minutes, subsequent water quenched from single phase beta region plus aged at 482°C/538°C). The results conclude that solution treatment carried for 45 minutes and aged at 482°C/538°C achieved high tensile strength with improvement in ductility. This is due to less nucleation sites of alpha precipitates along the grain boundaries for the 45 minutes solution treated specimens. The Young’s modulus evaluated for solution treated (78GPa), aged at 482°C (105GPa) and 538°C (103GPa), the increase in aged conditions is due to the formation of alpha precipitates throughout the matrix and makes the alloy two phase alpha-beta system.Keywords: Metastable beta, alpha precipitates, solution treatment, tensile strength, Young’s modulus.

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

“…The T β value strongly depends on the alloying elements: α-stabilizers increase T β , β-stabilizers decrease T β , while the neutral elements do not change T β [42]. Equation (1) to find the T β value is given below [32]:…”

“…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].…”

Heat Treatment of Metastable Beta Titanium Alloys

“…On the other hand, with the same holding time (8 h), 18% ductility along with a considerable decrease in the tensile strength is obtained by increasing the aging temperature to 560°C; the difference is attributed to the variation in the size of the acicular α precipitates [28]. The influence of aging on Young's modulus and ductility of Ti-15-3 alloy was clearly brought out by Naresh Kumar et al [23]. Hardenability of the beta Ti alloy is proportional to the content of the beta stabilizer.…”