The Atomic Defect Relaxation Processes in the Ti–Mo Alloys

Abstract

The relaxation processes correlated to atomic defects were investigated by the internal friction method using a multifunctional internal friction apparatus for TiMo alloys. The microstructures of the TiMo 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 ¢ phase increases and ¡ phase decreases in volume with increasing Mo content for the furnace-cooled alloys. Similarly, the ¢ M 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 Ti24 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 Ti3Mo and Ti5Mo alloys. Relaxation parameters of P1 peak are H wq1 = 1.56 « 0.1 eV and¸0 wq1 = 2.5 © 10 ¹16«0.1 s and those of P2 peak are H wq2 = 2.3 « 0.1 eV and¸0 wq2 = 2.1 © 10 ¹17«0.1 s for the water-quenched Ti5Mo alloy, respectively. The P1 peak is attributed to the stressinduced short-range ordering of oxygen complexes around Ti atoms in the TiMo alloys. The increase of the P1 peak height with increasing Mo content is attributed to the increase of ¢ phase in volume. The P2 peak is resulted from the interaction of MoO atoms or the reorientation of MoMo atomic pairs by means of vacancies. The MoO 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.

The Influences of Third Alloying Element on the Internal Friction Behavior and the Mechanical Properties in the Water Quenched Ti-12Mo Alloys

“…In contrast, the Ti-Mo alloys will form α , (with a hcp structure), α ,, (with an orthorhombic structure), βM (metastable β ) or their combination, which is dependent on Mo content when Ti-Mo alloys are rapidly cooled [3,10,11,13]. It is confirmed that the water quenched Ti-12Mo alloy possesses α ,, +βM phases [12].…”

“…The present P1 and P2 peaks has been investigated in Ref. [12]. That the P1 peak height increases with increasing Mo content can be attributed to the increase of β phase and oxygen in amount.…”

“…The P2 peak is deduced to be 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 and the vacancy volume is also increased when Mo content is increased, resulting in the increase of both the peak temperature and the activation energy of the P2 peak [12]. Fig.…”

“…Therefore, the Ti-Mo alloys have been also extensively studied as one of the β-type Ti alloys for biomedical applications [6][7][8][9][10]. The reported results are helpful for our understanding for the mechanism of high performance of Ti-Mo alloys [9][10][11][12], In which the internal friction mechanism of Ti-Mo alloys and the influences of Mo content and heat treatments on the internal friction behavior are described. However, it is not yet clear what changes may take place when the third element is added to Ti-12Mo alloys in the internal friction.…”

Structural Changes due to Heating and Stress Loading of Metastable Quenched Martensite Structures in Ti–(10–20) mass% Nb Alloys

“…The atomic defects in metals, such as quenched-in vacancies or interstitial elements, have important effects on their physical, mechanical properties and anelasticity, which is generally characterized by internal friction. 37) It is also reported that concentrations of quenched-in vacancies since it has been found that point defects play an important role in martensitic transformation. 38) We hypothesize that the change in Young's modulus and internal friction are affected by the change in the state of the quenched metastable martensite phase.…”