Stabilizing the body centered cubic crystal in titanium alloys by a nano-scale concentration modulation

Abstract

It is well-known that the body centered cubic (bcc) crystal in titanium alloys reaches its stability limit as the electron-to-atom (e/a) ratio of the alloy drops down to ~4.24. This critical value, however, is much higher than that of a multifunctional bcc type alloy (e/a = 4.15). Here we demonstrate that a nano-scale concentration modulation created by spinodal decomposition is what stabilizes the bcc crystal of the alloy. Aided by such a nano-scale concentration heterogeneity, unexpected properties from its chemically homogeneous counterpart are obtained. This provides a new strategy to design functional titanium alloys by tuning the spinodal decomposition.

Tracing the coupled atomic shear and shuffle for a cubic to a hexagonal crystal transition

“…Contributed by the nano-scale Nb modulation [27], the alloy is free of the  phase, as evidenced by the in-situ SXRD profiles in Fig. 1c.…”

Review of the Design of Titanium Alloys with Low Elastic Modulus as Implant Materials

“…[115] Many previous results proved that the phase stability of Ti alloys is related to the e/a ratio. [103,116,117] The as-quenched phase constitutions of Ti alloys are reported as a function of the e/a ratio, as shown in Figure 5. [118] It shows that the stability of the β phase in Ti alloys increases with the e/a ratio.…”

“…That is a key reason for low modulus. The elastic modulus of multicomponent Ti alloys [17,28,32,116,118,[122][123][124][125] against e/a ratio in Figure 7 indicates that the relationship between elastic modulus and e/a ratio in multicomponent Ti alloys is similar to binaries.…”

Significantly fast spinodal decomposition and inhomogeneous nanoscale martensitic transformation in Ti–Nb–O alloys

“…In Ti-Nb binary system, the β phase separation region does not exist in the equilibrium phase diagram but it appears in the metastable phase diagram considering only the β and ω phases [14]. The spinodal decomposition in Ti-Nb-based alloys has been observed experimentally in a Ti-Nb-Ta-Zr alloy via three-dimensional atom-probe tomography [15,16]. It has been suggested that the MT behavior and mechanical properties of the alloy can be influenced by the concentration modulation of Ti and Nb introduced by the spinodal decomposition [17].…”