Yunyun Liu

INTERACTION BETWEEN ND-RICH PHASE PARTICLES AND LIQUID-SOLID INTERFACE IN AS-CAST TI-5AL-4SN-2ZR-1MO-0.25SI-1ND TITANIUM-ALLOY

The composition (wt%) of ingot fir this investigation is 86.75%Ti, 5%Al, 4%Sn, 2%Zr, 1%Mo, 0.25%Si, 1%Nd. The alloy was prepared by vacuum arc melting in the form of buttons of mass 500 kg, which was remelted three times repeatedly to obtain homogeneous composition. The Nd-rich phase particles in the as-cast Ti-55 alloy are about 1.2{approximately}11.07 {micro}m and uniformly distribute in the matrix. The shapes of the particles are mainly ellipsoids together with short needle-like and blocky morphologies. The calculated diameter of the Nd-rich phase particles is {approximately} 10 {micro}m, which is within the 1.2{approximately}11.07 {micro}m range of the particle diameter experimentally measured in the as-cast Ti-55 alloy. The practical interface velocity is three orders of magnitude greater than V c, and the Nd-rich phase particles in the as-cast Ti-55 alloy are trapped by the liquid-solid interface.

Eutectic precipitation of melt quenched titanium-silicon-neodymium alloy

Titanium based metallic glasses have attracted keen interest because of the promise of industrial applications owing to their improves corrosion resistance, better mechanical properties, occurrence of superconductivity and superior magnetic properties. The titanium alloy systems where metallic glass has been obtained include Ti-Cu, Ti-Be, Ti-Si, Ti-B. Polk et al. had reported that they were able to produce an amorphous phase in binary Ti[sub 80]Si[sub 20] alloy system by using an arc-melting piston and anvil apparatus. In the present study, the authors have investigated the effect of adding rare earth element Nd on eutective precipitation of the amorphous Ti[sub 80]Si[sub 20] alloy and the orientation relationship which exists between the [beta]-Ti and Ti[sub 5]Si[sub 3].

A 2 micron passively Q-switched bulk state pulsed laser based on WS2

We report a 2 micron passively Q-switched bulk state pulsed laser with a pulse of 430 ns based on graphene-like 2D WS2 nanosheets. To the best of our knowledge, it is the shortest pulse compared with other bulk state lasers based on WS2 saturable absorbers at this waveband. The WS2 nanosheets are prepared through a facile hydrothermal reaction. Its max output power and pulse energy are 488 mW and 5.422 μJ, respectively. The wavelength is distributed from 1934 to 1942 nm. These results reveal that WS2 is a promising nanomaterial in the fields of photonics and electronics.

Co-effects of Yb 3+ sensitization and Pr 3+ deactivation to enhance 2.7 μm mid-infrared emission of Er 3+ in CaLaGa 3 O 7 crystal

Er3+/Yb3+/Pr3+: CaLaGa3O7 crystal was successfully grown by the Czochralski method. Detailed spectroscopic analyses of Er3+/Pr3+: CaLaGa3O7, Er3+/Yb3+: CaLaGa3O7 and Er3+/Yb3+/Pr3+: CaLaGa3O7 crystals were carried out. Compared with Er3+/Pr3+: CaLaGa3O7 and Er3+/Yb3+: CaLaGa3O7 crystals, Er3+/Yb3+/Pr3+: CaLaGa3O7 crystal not only shows a better absorption characteristic but also exhibits weaker up-conversion and near-infrared emissions, as well as superior mid-infrared emission. Furthermore, the self-termination effect for the 2.7 μm erbium laser is suppressed successfully since the fluorescence lifetime of the 4I13/2 lower level of Er3+ decreases markedly while that of the upper 4I11/2 level falls slightly in Er3+/Yb3+/Pr3+: CaLaGa3O7 crystal. Besides, the sensitization effect of Yb3+ and deactivation effect of Pr3+ ions as well as the energy transfer mechanism in Er3+/Yb3+/Pr3+: CaLaGa3O7 crystal were studied in this work. Moreover, energy transfer microparameters between Yb3+ and Er3+ were also calculated and analyzed based on Dexters model. In conclusion, the introduction of Yb3+ and Pr3+ is favorable for achieving an enhanced 2.7 μm emission in Er3+/Yb3+/Pr3+: CaLaGa3O7 crystal which can act as a promising candidate for mid-infrared lasers.

Direct observation of the nucleation of rare-earth-rich phase particles in rapidly solidified Ti-5Al-4Sn-2Zr-1Mo-0.25Si-1Nd alloy

Ti-5Al~4Sn-2Zr-lMo-0.25Si-1Nd is a near-alpha high temperature titanium alloy offering excellent tensile strength and good creep resistance up to 550°C together with improved fatigue strength. Addition of 1 wt% Nd to Ti-A1-Sn-Zr-Mo-Si system results in a uniform distribution of incoherent dispersoids and improves high temperature properties [1]. There have been many studies of rare earth additions to titanium alloys [2-6], but most work placed emphasis on binary or ternary alloys: none systematically reported Nd addition to high temperature titanium alloys such as the Ti-A1-Sn-ZrMo-Si system. It is well known that rapid solidification prevents kinetic growth of crystals, and even causes the formation of amorphous phases. It is possible that the nucleation process of the rare-earth-rich phase particles in Ti-5Al-4Sn-2Zr-lMo-0.25Si-lNd alloy can be clearly observed. By using an arc-melting piston and anvil apparatus, rapidly solidified Ti-5A14Sn-2Zr-lMo-0.25Si-lNd alloy flakes, 30-60/~m thick, were obtained. The observation was performed in a top-entry JEOL 2000 EXII high resolution electron microscope (HREM) with a point-to-point resolution of 0.21 nm. The foils were prepared by electrothinning in a methanol, butylethanol and perchloric acid mixture cooled to about -30 °C. A HREM image of a typical rare-earth-rich phase particle and matrix is given in Fig. 1. It can be seen that the matrix is in a crystalline state, and the rareearth-rich phase particle is amorphous. When the matrix has solidified, the rare-earth-rich phase remains liquid within a certain temperature range. According to the diffraction pattern, the matrix is a Ti, and the lattice fringes in the matrix are from the (0 0 0 2) plane. The contrast between the matrix and particle is mainly due to the lattice fringes (or to the rows of well-defined bright spots). EDAX results show that the amorphous phase consists of Nd and Sn, and the particles can be denoted as the rareearth-rich phase. Region V of Fig. 1 shows that a partial crystallization of the rare-earth-rich phase particle appears at the boundary between matrix and rare-earth-rich phase particle. Some rare-earth-rich phase particles begin to nucleate after matrix crystallization. It is clear that the nucleation of the rare-earth-rich phase Figure l HREM image of partially nucleated rare-earth-rich phase particle in the as-quenched Ti-5A1-4Sn 2Zl~lMo-0.25SilNd alloy.

A study of the microstructure of melt-quenched high-temperature Ti-5Al-4Sn-2Zr-1Mo-0.25Si-1Nd alloy

Abstract The microstructural morphology of the melt-quenched high-temperature Ti-55 alloy consists of a uniform distribution of bands of ultrafine Nd-rich phase particles. The calculated diameter of the particles is 6.648 nm, which is within the 6–15 nm range observed experimentally. The matrix first solidifies and engulfs the Nd-rich liquid droplets, and then the liquid droplets crystallize. Finally, bands of ultrafine particles are formed parallel to the advancing solidification plane-front.