Anelastic relaxation associated to phase transformations and interstitial atoms in the Ti-35Nb-7Zr alloy

Ti-35Nb-7Zr (wt.%) alloy was analyzed by mechanical spectroscopy. The results showed a relaxation peak, involving components of phase transformations and matrix-interstitial interactions and substitutional-interstitial interactions. The phase transformation β → ω in the first thermal cycle was identified by increases in elastic modulus and Vickers hardness. In the subsequent thermal cycles, a fall in the strength of relaxation and stabilization of the dynamical elastic modulus were associated with variation in the fraction of ω-phase formed and nucleation of the α-phase, as indicated by DSC, XRD and SEM-EDX results. In addition, once the strength of relaxation was stabilized shifts of the relaxation peak to higher temperatures were observed with increasing oscillating frequency. This frequency dependence of the peak was accompanied by a change in the oscillation frequency that is characteristic of a Snoek-type relaxation. Thus, this behavior can be related to stress-induced reorientation of interstitial oxygen atoms with matrix (Ti) and substitutional (Nb) atoms in the bcc structure of the β-phase.