The Atomic Defect Relaxation Processes in the Ti–Mo Alloys
Z. C. Zhou, Y. F. Yang, J. Du, S. Y. Gu, X. B. Zhu, Y. J. Yan, M. Sun
The relaxation processes correlated to atomic defects were investigated by the internal friction method using a multifunctional internal friction apparatus for Ti–Mo alloys. The microstructures of the Ti–Mo alloys with different Mo content and heat treatments were observed using an optic microscopy and a scanning electronic microscopy. Their phase constitutions were detected by X-ray diffraction (XRD). The β phase increases and α phase decreases in volume with increasing Mo content for the furnace-cooled alloys. Similarly, the βM phase volume increases when Mo content is increased. The two relaxational internal friction peaks, named as P1 for the low temperature peak and P2 for the high temperature peak, respectively, are found on the internal friction temperature dependent curves in the alloys. The two peaks always appear in the present experimental specimens with different Mo content and different heat treatments except for the water quenched Ti–24 Mo alloys. The P1 and P2 peaks are all influenced by Mo content and heat treatments and related to phase constitutions and microstructures. The P1 peak height increases with increasing Mo content for the water quenched alloys and the P1 peak temperature is not changed with Mo content. The P2 peak height increases also with increasing Mo content and the P2 peak temperature is raised when Mo content is increased but for the water quenched Ti–3Mo and Ti–5Mo alloys. Relaxation parameters of P1 peak are Hwq1 = 1.56 ± 0.1 eV and τ0wq1 = 2.5 × 10−16±0.1 s and those of P2 peak are Hwq2 = 2.3 ± 0.1 eV and τ0wq2 = 2.1 × 10−17±0.1 s for the water-quenched Ti–5Mo alloy, respectively. The P1 peak is attributed to the stress-induced short-range ordering of oxygen complexes around Ti atoms in the Ti–Mo alloys. The increase of the P1 peak height with increasing Mo content is attributed to the increase of β phase in volume. The P2 peak is resulted from the interaction of Mo–O atoms or the reorientation of Mo–Mo atomic pairs by means of vacancies. The Mo–O interaction is strengthened when Mo content is increased, which results in the increase of both the peak temperature and the activation energy of the P2 peak.