偏量应变定标模型在Nb_3Sn股线中的应用

采用Pacman弹簧装置测量在不同磁场,温度和应变条件下Nb3Sn多芯股线的V-I特征曲线。外部磁场变化范围由4T到14T,温度变化由4.2K至10K,材料轴向应变变化范围在-0.9%～+0.6%。在此基础上详细介绍了近年来应用广泛的三维偏量应变定标模型,通过该定标模型模拟了Nb3Sn超导材料临界电流Ic随应变状态的变化规律。     

Graphene micro-substrate-induced π gap expansion in MgB2

The lattice effect induced by tensile strain on the superconductivity of graphene–MgB₂ composites was studied systematically to deduce the electron–phonon coupling (EPC) and the multiple superconducting gap behavior. Compared with nano-carbon doped MgB₂, graphene–MgB₂ composites show larger lattice parameters and higher critical superconducting transition temperatures (T_c). The EPC strength of MgB₂ with ∼2 wt.% graphene addition is even higher than that of the pure reference sample, as estimated from the Sommerfeld constant. The π gap was found to be expanded by graphene addition through the analysis of heat capacity data, and it is responsible for both the enhanced EPC strength and the weak dependence of T_c on the graphene content.     

Roles of humidity and heat treatment temperatures on YBa2Cu3O7-x coated conductors by trifluoroacetic acid-metal organic deposition process

YBa₂Cu₃O_7−x(YBCO) films were fabricated on an LAO substrate using the trifluoroacetic acid-metal organic deposition (TFA-MOD) method and the effects of the humidity and heat treatment temperatures on the microstructure, degree of texture and critical properties of the films were evaluated. In order to understand the combined effects of the humidity and the calcining and firing temperatures on critical properties, heat-treatment was performed at various temperatures with the other processing variables fixed. The films were calcined at 400–430 and fired at 750–800 °C in a 0–12.1% humidified Ar-O₂ atmosphere. The texture was determined by pole-figure analysis. The amount of the BaF₂ phase was effectively reduced and a sharp and strong biaxial texture was formed under a humidified atmosphere, which led to increased critical properties. In addition, the microstructure varied significantly with firing temperature but changed little with calcining temperature. The highest I_C of 40 A/cm-width, which corresponds to J_C value of 1.8 MA/cm², was obtained for the films fired at 775 (in 12.1% humidity) after calcining at 400–430 °C. It is likely that °C the highest I_C value is due to the formation of a more pure YBCO phase, c-axis grains, and a denser microstructure.     

STUDY ON HIGH TEMPERATURE DEFORMATION CHARACTERISTICS OF Cu–0.23%Al2O3 DISPERSION–STRENGTHENED COPPER ALLOY

利用Gleeble--1500热模拟机、金相以及透射电镜对Cu--0.23%Al₂O₃(体积分数)合金高温塑性变形过程中的流变应力和显微组织变化规律进行了研究. 研究结果表明, Cu--0.23%Al₂O₃合金在热压缩过程中,热压缩条件不同流变应力变化规律会有所差异. 此外, 还求得了该合金高温变形的平均激活能和其他相关材料常数, 据此建立了峰值屈服应力--应变速率--温度之间的本构方程. 随热压缩温度的升高, 基体内动态再结晶晶粒尺寸和数量不断增加, 而在同一温度压缩时, 随应变速率的增加,组织分布不均匀性有所增加, 亚晶尺寸不断减小, 位错密度先增加后降低.     

Synthesis temperature of Ba4CuPt2O9 compounds and the influence of their addition on the orientation of the c-axes of fluorine-doped YBCO superconductors

An experimental study has been carried out to investigate the synergistic effect of Ba₄CuPt₂O₉ compounds on the critical current density of fluorine-doped YBCO superconductors. The Ba₄CuPt₂O₉ compounds were synthesized by a solid state reaction. It was found that the synthesis temperature of the Ba₄CuPt₂O₉ compounds was over 800°C, which was higher than that ever reported previously. In addition, the influence of Ba₄CuPt₂O₉ compounds on the critical current density of YBCO superconductors has been investigated using two types of Ba₄CuPt₂O₉ compounds: one is not heat-treated, i.e. source materials; and the other is heat-treated at 950°C. It was found that the former affected the orientation of the c-axes, but the latter did not have an influence on the orientation of the c-axes, but adversely affected the superconductivity of samples quenched at temperatures above 850°C.     

镁扩散制备Pr6O11掺杂的 MgB2块体临界电流密度和磁场性能研究

采用镁扩散方法制备了Pr₆O₁₁纳米颗粒添加的MgB₂超导块体,研究了Pr₆O₁₁掺杂对其临界电流密度(J_c),不可逆磁场(H_irr)和上临界磁场(H_c2)的影响。实验结果表明Pr₆O₁₁纳米颗粒掺杂明显提高了块体的J_c,H_irr和H_c2,但没有降低其超导转变温度T_c。在20 K自场条件下,质量比为1 wt.% Pr₆O₁₁掺杂的MgB₂块体的J_c较没掺杂样品提高了将近5倍, J_c=3.61×10₅A/cm₂。在10 K温度下,MgB₂块体H_c2 和H_irr较没掺杂样品分别提高了1.9 T and 2.6 T。同时讨论了Pr₆O₁₁纳米颗粒掺杂对MgB₂块体的电性能和磁通钉扎机制的影响。     

Alloyed W–(Co,Ni,Fe)–C phases for reaction sintering of hardmetals

It has been shown that W–Co–C phases could dissolve a substantial amount of metals such as V, Cr and Ta, which are known to positively influence the microstructure of hardmetals with respect to uniform grain size distribution and fine grain size. This offers a tool to circumvent the conventional doping of hardmetals with individual carbides. In the present study we used double- and triple-alloyed κ-W₉Co₃C₄ (i.e. κ-(W,V,Cr)₉Co₃C₄ and κ-(W,V,Cr,Ta)₉Co₃C₄) and applied a variety of sintering experiments to obtain WC–Co, WC–(Ti,Ta,Nb)C–Co and WC–(Ti,Ta,Nb)(C,N)–Co hardmetals. We also prepared κ-W₉Fe₃C₄, alloyed κ-W₉Ni₃C₄, and κ-W₉(Fe/Ni)₃C₄, and used the latter for sintering.     

Chemical polymerization of aniline using periodic acid in acetonitrile

The chemical polymerization of aniline in anhydrous medium was investigated using periodic acid, H₅IO₆ as an oxidant. This is the first time that H₅IO₆ has been used as an oxidant in the chemical synthesis of conductive polymers. The product was characterized by FTIR, UV–vis spectroscopies, scanning electron microscope (SEM), energy dispersive X-ray (EDX) spectroscopy, thermogravimetric (TG) analysis, and electrical conductivity measurements. EDX and thermogravimetric analysis showed that Pani includes ClO₄⁻ and iodine or iodide ion as dopants. Electrical conductivity of polyaniline with H₅IO₆ was measured as 100 S cm⁻¹. H₅IO₆ oxidant produces first IO₃⁻ and then I₂. Therefore, it could ensure both oxidation of aniline by IO₃⁻ and then doping polyaniline with I₂, without any residual oxidant contamination. I₂, which is a well known extrinsic dopant, was produced intrinsically in this study. Thus, H₅IO₆ was found to be an effective oxidant material for the chemical polymerization of aniline.     

Infrared spectroscopic properties of Tm, Ho:NaY(WO4)2 single crystals

Singly doped and Tm³⁺/Ho³⁺ co-doped NaY(WO₄)₂ single crystals were grown successfully by Czochralski method. The room temperature polarized absorption and fluorescence spectra as well as the decay curves were measured. Spectroscopic parameters related to the laser operation around 2.0 μm via the ³F₄ → ³H₆ (Tm³⁺) and ⁵I₇ → ⁵I₈ (Ho³⁺) transitions have been evaluated. The energy level scheme and energy transfer processes of Tm³⁺ and Ho³⁺ were analyzed.     

DEFORMATION BEHAVIOR AND CONSTITUTIVE EQUATION FOR Zr55Cu30Al10Ni5 BULK METALLIC GLASS IN SUPERCOOLED LIQUID REGION

Zr₅₅Cu₃₀Al₁₀Ni₅块体非晶合金(BMG)在过冷液态区内的单向压缩实验表明: 材料在过冷液态区内的形变行为强烈依赖于温度和变形速率. 随着应变速率的增加, 材料的流变特征由Newtonian流变转变为非Newtonian流变.利用扩展指数本构方程模型建立了非晶合金的流变应力、应变速率和温度的关系.     

受控短路过渡CO2焊焊接电流波形参数优化

对于波控短路过渡CO₂焊,电弧峰值电流I_pa,电弧基值电流I_ba以及由峰值电流切换到基值电流所用的时间(拖尾时间t_w)等电流波形参数是可调的,它们对过渡稳定性和焊缝质量具有很大影响,利用正交试验,对不同送丝速度下电流波形参数进行了优化.结果表明,电弧峰值电流的影响最大.送丝速度为320 cm/min时,电流波形参数I_pa,I_ba和t_w无论如何调整,飞溅率均在2.5%以上,焊缝表面质量差;送丝速度为360~400 cm/min时,最优电流波形参数为:I_pa=440 A,I_ba=50 A,t_w=0.6 ms.而在400 cm/min的送丝速度下,在宽广的电流波形参数范围内(I_pa为440~480 A,I_ba为30~50A,t_w为0.6~0.8 ms)均可获得飞溅率极低、焊缝表面质量好的稳定焊接过程.     

Process–structure–property relations of micron thick Gd2O3 films deposited by reactive electron-beam physical vapor deposition (EB-PVD)

Thick polycrystalline gadolinium oxide (Gd₂O₃) films up to 11 μm in thickness were deposited via reactive electron beam-physical vapor deposition (EB-PVD) on silicon (111) substrates for use in neutron radiation detection. The effects of coating thickness, substrate temperature, and oxygen flow on film structural, electrical and optical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), capacitance–voltage (C–V) measurements, and ultraviolet–visible (UV–Vis) spectroscopy. Films were characterized as either monoclinic or mixed monoclinic and cubic phase depending on deposition parameters. Increasing the deposition temperature resulted in increased film crystallinity and cubic phase volume while decreasing the O₂ flow rate resulted in increased volume of the monoclinic phase. Evidence of a thickness dependent crystallography is also presented. Electrical property measurements showed thin film dielectric constant could be tailored between 12 and 20 at 1 MHz frequency by decreasing the oxygen flow rate at deposition temperatures of 250 °C which is attributed to an increased presence of the monoclinic phase and increased film density. Band gap values were calculated from transmission measurements and ranged between 5.44 and 5.96 eV.     

Oxidation behavior of micro-sized Al2O3–TiC–Co composites prepared from cobalt-coated powders

The oxidation behavior of hot-pressed Al₂O₃–TiC–Co composites prepared from cobalt-coated powders has been studied in air in the temperature range from 200 °C to 1000 °C for 25 h. The oxidation resistance of Al₂O₃–TiC–Co composites increases with the increase of sintering temperature at 800 °C and 1000 °C. The oxidation surfaces were studied by XRD and SEM. The oxidation kinetics of Al₂O₃–TiC–Co composites follows a rate that is faster than the parabolic-rate law at 800 °C and 1000 °C. The mechanism of oxidation has been analyzed using thermodynamic and kinetic considerations.     

As-deformed filament's density and transport currents of MgB2/Ti/Glidcop wire

Filamentary MgB₂/Ti/Glidcop wire has been manufactured by in situ process using hydrostatic extrusion, cold drawing and finally subjected to high pressure and standard densifications. Filament density of as-deformed wires was evaluated by micro-hardness measurements and related to applied deformation. It was found that filament's density and uniformity in as-deformed wire have a strong effect on the critical current density (J_c) of annealed samples. The highest J_c was measured for the filaments densified by cold isostatic pressing with 2 GPa and also for rotary swaged ones showing the best uniformity. Presented results showed the importance of filament density and homogeneity and also demonstrate suitability of hydrostatic extrusion for uniform long-length filamentary MgB₂ wires production.     

Tunable red-green-blue multicolor luminescence in Yb/Tm/Ho:Gd3Ga5O12 nano-crystals

The Yb³⁺/Tm³⁺/Ho³⁺: Gd₃Ga₅O₁₂ nano-crystals have been successfully prepared via a citric acid complex procedure. The luminescence spectra were measured and the up-conversion processes were discussed. By means of adjusting the doping concentrations of Yb³⁺/Tm³⁺/Ho³⁺, the red-green-blue up-conversion luminescence changed obviously. Results indicated that the ratio of red-green-blue up-conversion emissions enhanced heavily with the increasing concentrations of Tm³⁺ doped in the Yb³⁺/Tm³⁺/Ho³⁺:Gd₃Ga₅O₁₂ nano-crystals, which was rooted in the three-photon resonant cross relaxation processes(¹G₄ (Tm) + ⁵I₇ (Ho) → ³H₅ (Tm) + ⁵S₂ (Ho)). The tunable red-green-blue luminescence could be used in the fields of display, illumination, and photonics such as the white light generation.     

High temperature thermo-physical properties and thermal shock behavior of metal–diborides-based composites

The thermo-mechanical properties and thermal shock resistance of two metal diborides composites, HfB₂ with 20 vol.% SiC and HfB₂ with 20 vol.% SiC and 10 vol.% AlN, were investigated. Results showed that the composite HfB₂–SiC–AlN had a higher specific heat capacity than that of composite HfB₂–SiC. However, the occurrence of a Si–Al–O phase in the grain boundaries increased the heat flow resistance at grain boundaries, resulting in decrease thermal diffusivity and thermal conductivity. The calculated thermal shock resistance parameters indicated that the addition of AlN increased the resistance against crack initiation and crack propagation of composite, corresponding to the increase in critical thermal shock temperature difference from 400 to 600 °C.     

Synthesis and crystal structure of Ba3Si4C2

SiC powder prepared by the Na flux method at 1023 K for 24 h and Ba were used as starting materials for synthesis of tribarium tetrasilicide acetylenide, Ba₃Si₄C₂. Single crystals of the compound were obtained by heating the starting materials with Na at 1123 K for 1 h and by cooling to 573 K at a cooling rate of −5.5 K/h. The single crystal X-ray diffraction peaks were indexed with tetragonal cell dimensions of a = 8.7693(4) and c = 12.3885(6) Å, space group I4/mcm (No.140). Ba₃Si₄C₂ has the Ba₃Ge₄C₂ type structure which can be described as a cluster-replacement derivative of perovskite (CaTiO₃), and contains isolated anion groups of slightly compressed [Si₄]⁴⁻ tetrahedra and [C₂]²⁻ dumbbells. The electrical conductivity measured for a not well-sintered polycrystalline sample was 2.6 × 10⁻²–7 × 10⁻³ S cm⁻¹ in the temperature range of 370–600 K and slightly increased with increasing temperature. The Seebeck coefficient showed negative values of around −200 to −300 μV K⁻¹.     

Structural and electrical properties of Gd(Ni1/2Zr1/2)O3

The Gd(Ni_1/2Zr_1/2)O₃ (GNZ) ceramic is synthesized by the solid-state reaction technique. The X-ray diffraction pattern of the sample shows monoclinic phase at room temperature. The dielectric dispersion of the material is investigated in the temperature range from 303 K to 673 K and in the frequency range from 100 Hz to 1 MHz. The relaxation peak is observed in the frequency dependence of the loss tangent. The relaxation time at different temperatures is found to obey Arrhenius law having activation energy of 1.1 eV which indicates the hopping of ions at the lattice site and may be responsible for the dielectric relaxation of GNZ. The scaling behaviour of loss tangent suggests that the relaxation mechanism is temperature independent. The frequency dependent conductivity spectra follow the power law. In the impedance formalism, the Cole-Cole model is used to study the relaxation mechanism of GNZ.     

Thermal and electrical properties of TiB2–MoSi2

The present communication reports the effect of MoSi₂ addition on high temperature thermal conductivity and room temperature (RT) electrical properties of TiB₂. The thermal diffusivity and the thermal conductivity of the hot pressed TiB₂–MoSi₂ samples were measured over a range from room temperature to 1000 °C using the laser-flash technique, while electrical resistivity was measured at RT using a four linear probe method. The reciprocal of thermal diffusivity of TiB₂ samples exhibit linear dependence on temperature and the measured thermal conductivity of TiB₂-2.5% MoSi₂ composites correlate well with the theoretical predictions from Hashin’s model and Hasselman and Johnson’s model. A common observation is that the thermal conductivity of all the samples slightly increases with temperature (up to 200 °C) and then decreases with further increasing temperature. It is interesting to note that both the thermal conductivity and electrical conductivity of TiB₂ samples enhanced with the addition of 2.5 wt.% MoSi₂ sinter additive. Among all the samples, TiB₂-2.5 wt.% MoSi₂ ceramics measured with high thermal conductivity (77 W/mK) and low electrical resistivity (12 μΩ-cm) at room temperature. Such an improvement in properties can be attributed to its high density and low volume fraction of porosity. On the other hand, both the thermal and electrical properties of TiB₂ were adversely affected with further increasing the amount of MoSi₂ (10 wt.%).     

Plasma spraying of Al2O3–WO3 composite coatings

Al₂O₃–WO₃ oxide composites are of considerable interest as solid acid catalysts in the petrochemical industry. Typically they consist of a monolayer of WO₃ dispersed over a high surface area alumina support. The aim of this work was to form a single layer Al₂O₃–WO₃ composite coating by plasma spraying. Ammonium metatungstate was dispersed through porous alumina particles and transformed to WO₃ by heat treatment. WO₃ doped powders were plasma sprayed using “low” and “high” enthalpy plasma systems. Plasma spraying led to dramatic changes in the WO₃ oxide to form metallic tungsten, a metastable Al₂O₃–W solid solution and the mixed oxide Al₂(WO₄)₃. The mechanisms accounting for these transformations are discussed.