稀有金属材料与工程最新文献

The Al₃Zr-η′ core-shell particles were observed in the Al-12Zn-2.4Mg-1.1Cu-0.5Ni-0.2Zr alloy using high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). Two types of Al₃Zr particles appear in the Al matrix: one is a standalone Al₃Zr particle that is coherent with the matrix, and the other is an as-core Al₃Zr particle acting as a nucleation site of the η′ precipitates, resulting in a core-shell particle which is semi-coherent with the matrix. The shell is composed of η′ precipitates with four variants. The strain in the as-core Al₃Zr is lower than that in the standalone Al₃Zr, and a considerable amount of strain exists across the interfacial regions between the η′ precipitates and the matrix.

Diffusion couples for Co-rich fcc Co-Cr-V alloys were prepared, all of which were annealed at 1473 K for 259 200 s. The interdiffusion coefficients in fcc Co-Cr-V ternary systems were investigated by means of Whittle and Green method with the help of electronic-probe microanalysis (EPMA). On the basis of the thermodynamic parameters available in the literature, the interdiffusion data were critically assessed to develop the atomic mobilities of the fcc Co-Cr-V alloys via the DICTRA software. Comprehensive comparisons between the calculated and experimental diffusion coefficients show that the experimental data can be well reproduced by the atomic mobilities obtained in this work. And the validity of the diffusion mobilities was tested by simulating the concentration-distance profiles and diffusion paths in diffusion couples.

The effects of cryogenic treatment prior to hot rolling on the strength, toughness and ductility of as-cast AZ31 magnesium alloy plates were investigated. The cryogenic treatment conditions were −60 °C/12 h, −120 °C/12 h, −180 °C/12 h, −60 °C/2 h, and −180 °C/2 h. Experimental results show that appropriate cryogenic treatment conditions can significantly refine the grain size and the improve strength, toughness and ductility. A large number of twins appear in both kinds of samples cryogenically treated for 2 h. The sample experienced cryogenic treatment for 12 h at −60 °C followed by rolling process shows the finest and most uniform and increase in yield strength by 25.8%. Meanwhile, a four-time increase in extension rate (3.06% to 12.31%) is attains. The tensile fracture present a mixed-mode fracture, which is characteristic of brittle and ductile fracture mechanisms.

This work developed a simple and low-cost method to achieve superior superhydrophobicity and corrosion resistance of 5A05 Al alloy. The microscale wrinkles covered with nanoscale craters were prepared by a one-step wire electrical discharge machining process. Meanwhile, the wettability and corrosion resistance of the as-prepared structures were investigated after the low-surface-energy modification. The results show that the modified surface exhibits excellent superhydrophobicity with a water contact angle (CA) of 152.7° and a rolling angle (RA) of 7.1°. Furthermore, its corrosion resistance was assessed by electrochemical tests. Ultimately, owing to the trapped air in micro-nano structures, the solid-air-liquid interface helps to resist seawater penetration on the superhydrophobic surface and significantly enhances its corrosion resistance.

Ni7W/Ni12W/Ni7W composite substrates for YBa₂Cu₃O_7-δ coated conductors were prepared by rolling assisted biaxially textured substrates route. A threefold intermediate annealing at different temperatures was introduced in the rolling process of Ni7W/Ni12W/Ni7W composite substrates to optimize the deformation texture. The recovery microstructure and the deformation texture of latitude and longitude section were studied with X-ray diffraction and electron backscattered diffraction to reveal the possible mechanism of temperature effects on rolling and strong cube texture formation processes. The results show that the highest cube area fraction is found in sample intermediately annealed at 600 °C/60 min; in this way Ni7W/Ni12W/Ni7W composite substrates with high cube texture content of 95% (<10°) are obtained at a low recrystallization annealing temperature. Crystal orientation maps reveal that a higher amount of cube orientation exists in its recovery and initial recrystallization samples. Point to point misorientation files confirm the high grain boundary angle of these cube grains, which strongly boost the cube texture formation during subsequent recrystallization.

A NiFeBSiNb amorphous/nanocrystalline composite coating was prepared through flame thermal spraying, where a gas atomized alloy powder substituted an amorphous powder. The microstructure and thermal behavior of the laboratory-produced powders and the produced as-sprayed coating were characterized. The results demonstrate that the powder, which is spherical or ellipsoidal, is mainly composed of Nb₂Ni₂₁B₆ and (Ni,Fe)₂₃B₆ crystalline phases, whereas the as-sprayed coating consists of a glassy structure and certain nanocrystalline phases. It is obtained through calculations that the R_c (critical cooling rate) of the powder and the as-sprayed coating for the amorphous phase formations is 6.01×10⁵ and 4.56×10³ K/s, respectively. The explanation for the amorphous structure, as it occurred in the as-sprayed coating, is the rapid quenching from the melt at the cooling rates which exceeds the critical cooling rate R_c. The as-sprayed amorphous coatings displays a low friction coefficient of 0.17 and excellent wear resistance.

In order to overcome the defects of high over-potential and preparation cost existing in traditional Pb alloy anodes, a new type aluminum foam/Pb-0.6 wt%Ag alloy composite anode (AF/Pb-0.6 wt%Ag anode) was produced. The electrochemical performance of AF/Pb-0.6 wt%Ag anode and traditional Pb-0.6 wt%Ag anode after 72 h galvanostatic polarization in 160 g/L H₂SO₄ solution was investigated comparatively by chronopotentiometry (CP), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and Tafel measurements. The results show that the anodic layer of AF/Pb-0.6 wt%Ag anode is more intact than that of the Pb-0.6 wt%Ag anode, and exhibits better corrosion resistance. Moreover, the AF/Pb-0.6 wt%Ag anode shows a lower stable anodic potential, which is consistent with higher PbO₂, lower PbO, PbO·PbSO₄ content and R_ct value obtained by CP and EIS measurements. It is also revealed that the AF/Pb-0.6 wt%Ag anode possesses a better oxygen evolution reaction (OER).

Grain boundary character and microstructural evolution during hot deformation of a high Nb-containing TiAl alloy with the composition of Ti-45Al-8.5Nb-(W, B, Y) was investigated. The plasma arc-melted alloy exhibits nearly lamellar microstructures with β/B2 phase precipitates along colony boundaries. The retained β/B2 phase rich in Ti, Nb and W and poor in Al is formed by the β→α transformation during nonequilibrium solidification. This β/B2 precipitation is caused by the high cooling rate, low atom diffusion rate of β stabilizers and different partition coefficients of the elements. B and Y elements exist mainly as borides and Y₂O₃, respectively. The morphology, size, composition and stability of β/B2 phase are determined by hot deformation. The high temperature and press enhance the elements diffusion, and thus the variation of the composition of β/B2 phase in deformed samples is obviously observed. When the samples are deformed in (α + γ) phase region, the transformation β/B2→α₂ takes place. Considering the different crystal structures of β/B2 and α₂ phases, there is a tendency for β/B2 phase to transform to a more closed packed structure of α₂ during deformation. The β/B2→ α₂ transformation is promoted by the hot deformation.

On international thermal nuclear experimental reactor (ITER) superconducting fusion device, Nb₃Sn composite strands have been applied to CICC (cable-in-conduit conductor) to undergo the impact of the magnet field above 12 T. The strain of Nb₃Sn-based conductor due to Lorentz forces leads to changes in critical current and coupling loss time constant. Therefore the study on the critical performance degradation of CICC is still inadequate, and the influence of the contact properties with strain on the coupling loss time constant is also insufficient. In order to calculate the coupling loss accurately and quickly, a new calculation model of coupling loss time constant was put forward in this paper. The model is expressed by a linear equation using some parameters such as the cabling sequence ratio, contact resistance and void fraction with strain main from electromagnetic force. In this model, the computation expression of cabling sequence ratio, as well as the contact resistance and the void fraction are obtained under the strain from cyclic electromagnetic load. Compared with numerical calculation using Gandalf and the traditional method, coupling loss calculated by the new model has a small error, and it is close to the engineering measurement.

The effects of the addition of Pr₆O₁₁ nanopowder on the critical current density (J_c), irreversible field (H_irr) and upper critical field (H_c2) of the MgB₂ bulks prepared by a Mg-diffusion method were investigated. The results show that the Pr₆O₁₁ nanopowder doping can significantly enhance the J_c, H_irr and H_c2 of the MgB₂ bulks, but has little effect on the superconducting transition temperature (T_c). At 20 K in a self-field, the J_c value of the 1 wt% Pr₆O₁₁-doped MgB₂ sample is 3.61×10⁵ A/cm², which is nearly 5 times larger than that of the undoped sample. In addition, at 10 K, the H_c2 and H_irr of the bulk increase by 1.9 and 2.6 T, respectively. The effect of Pr₆O₁₁-doping on superconductivity and flux pinning mechanism was also discussed.