MgB_2多芯超导线带材研究进展

回顾了近年来多芯MgB2超导线带材的主要研究进展,分析了包套材料的选取原则;比较了粉末套管法(PIT)、连续粉末装管成型工艺(CTFF)及中心镁扩散工艺(IMD)等几种常用的MgB2线带材加工制备技术的特点;评述了多芯MgB2线带材的磁通钉扎性能、交流损耗、稳定性与失超传播以及力学性能等方面的研究进展;同时简要回顾了多芯MgB2超导线带材的应用研究现状。     

AZ31B镁合金板材的织构

研究了AZ31B镁合金热轧、冷轧和热处理状态板材织构的特征以及对机械性能各向异性的影响.结果表明:轧制镁合金板材具有主要以基面织构为主的板织构,其基面平行于板面,其他织构组分相对较弱;冷轧后的基极密度中心围绕板横向向轧制方向旋转约18°;冷轧后在300℃热处理对织构分布特征影响不大.冷轧后的基面向轧制方向倾斜使该方向的塑性指标得到改善.     

钽丝的织构和再结晶行为研究

研究了变形钽丝在不同温度下退火后的织构演变和再结晶行为，发现1360℃退火后钽丝初次再结晶基本完成；1500℃退火后，钽丝中发生了二次再结晶，晶粒异常粗大。提出了拉拔钽丝的再结晶织构模型。     

镁合金AZ80A搅拌摩擦焊焊核区组织金属学演变

采用取像显微分析技术分析了变形镁合金AZ80A搅拌摩擦焊焊核区塑性条带间的金属学演变过程.结果表明:搅拌摩擦焊搭接头焊核区晶粒尺寸、极图、反极图以及晶粒的取向差均呈周期性的变化,组织结构呈条带分布,基体内部经历了周期性的动态再结晶过程.     

Dynamical Theory of a High-Temperature Superconductor Photo-Thermoelectrical Bolometer

In this paper, we develop a dynamic theory starting from the basic heat balance equation for a high-temperature superconductor (HTSC) photothermoelectrical bolometer. We include dynamics via a small infrared sinusoidal signal incident on the sensitive area of the bolometer. The sensitive area of the bolometer is considered to be approximately mm × mm, with a film thickness in the micron range. This area is a thermoelectrical junction between an HTSC—for example, YBCO—and a high thermoelectic figure of merit material—for example, BiSb—grown on a substrate—for example, Yttria stabilized zirconia (YSZ). The two legs of the thermocouple are connected in a parallel geometry. Heat is transferred by direct conductance to the substrate underneath as well as toward the cold end of the thermojunction—that is, Peltier heat in the plane of the substrate—is also taken into account. It is found that if the bolometer is operated under a voltage bias condition, there is substantial improvement in the response time and the responsivity of the bolometer. This appears to be due to the photothermoelectrical operation superimposed on the normally used photoelectrical operation.     

工业纯钛金属织构标准极图的计算及分析

工业纯钛中的金属织构会引起各向异性,获得织构信息及分析其演变规律对钛材加工与应用非常重要.本文利用单晶钛的晶体结构数据、乌氏网、极图与织构的定义,建立了纯钛的织构与特定晶面极图之间的对应关系,理论计算并绘制了纯钛部分织构的标准极图.基于塑性变形时基本滑移面与滑移方向的演变规律,构建了纯钛金属加工方式与织构之间的内在联系,可为六方系纯钛金属或合金的织构演变与表征提供理论基础。     

Fabrication of BSCCO Nanocrystal Superconductors

Nanocrystal materials have their special properties because of very small grain size.Nanocrystalsuperconductors were prepared by crystallizing the amorphous slices with nominal composition ofBi_(1.6)Pb_(0.4)Sr_2Ca_4Cu_5O_x at certain temperature.The measurements of R-Tcurve and x data prove allthe crystallized samples have superconducting transition though their Meissner effect is weak.All thenanocrystal superconductors are mainly constituent of Bi_2Sr_2CaCu_2O_y phase by the analysis ofX-ray diffraction.     

Analyses of the Pinning Mechanism for the Superconductor/Normal-Metal and Superconductor/Superconductor Multilayers

The vortex pinning force of superconductor(S)/normal-metal(N) multilayers, Nb/Ti and Nb_100−x Ti _x /Ti, and superconductor(S)/superconductor(S′) multilayers, Nb_100−x Ti _x /Nb and Nb₂₈Ti₇₂/Nb₆₅Ti₃₅, has been studied as a function of the layer thickness d for various compositions of x. The transverse pinning force density F _{p ⊥} acting perpendicular to the layer planes makes a peak around d∼ 2ξ_GL (ξ_GL: the GL coherence length) for both the S/N and S/S′ multilayers, where they exhibit the quasi-two-dimensional superconductivity. In contrast, the longitudinal pinning force density F _p‖ acting parallel to the layer plane hardly depends on d. The pinning mechanism inherent in the layered structure has been analyzed based on the GL free energy, which clarified that the effective pinning force due to the multilayer structure originates from the difference in the potential energy for the S/N multilayer and from the difference in the kinetic energy for the S/S′ multilayer between the constituent layers. The d dependence of the F _{p ⊥}, however, has been found to be qualitatively similar for the S/N and S/S′ multilayers.     

Microwave Power Dependence of Surface Resistance of High-Temperature Superconductor YBa2Cu3O y Films by Dielectric Resonator Method

The microwave power dependence of the surface resistance of YBa₂Cu₃O_y films of two different surface morphologies was measured using the dielectric resonator method. The dielectric resonator consisted of a high-quality sapphire rod sandwiched between two superconductor films. Measurements showed that the microwave power dependence of the surface resistance strongly depended on the surface morphology of the YBa₂Cu₃O_y film though the surface resistance of those films at low microwave power was comparable. In conclusion, the surface morphology is one of the reasons of the power dependence which is crucial for high power applications.     

Bi-based superconductors prepared with addition of CoFe2O4 for the design of a magnetic probe

We have investigated the microstructure and the magnetoresistivity of bismuth based superconductor bulks added with nano-sized CoFe₂O₄ particles (10 nm in diameter). Samples were prepared through the solid state reaction (SSR) technique by addition of CoFe₂O₄ nanoparticles during the last step of heat treatment. Phase examination using X-ray diffraction (XRD), morphology investigation by scanning electron microscope (SEM), microstructure and local chemical composition analyses using transmission electron microscope (TEM) coupled with energy dispersive X-ray spectroscope (EDXS), electrical resistance versus temperature ρ(T) under applied magnetic fields (B) and electrical resistance versus B at 77 K, ρ(B), were carried out. The CoFe₂O₄ added sample shows a great magnetoresistance to weak magnetic field at the temperature of liquid nitrogen (77 K). This result is attractive for practical, because CoFe₂O₄ added samples can be utilized as active elements in magnetic fields sensor devices.     

An Equation of State for High-Temperature Superconductor

In the present paper the expression of cohesive energy and the bulk modulus as a function of volume are formulated for high-T _c copper oxide superconductors. The model employed consists of long-range electrostatic Coulomb interaction and short-range overlap repulsion. The short-range overlap potential is considered in the Born–Landé inverse power form. The model parameters of the Born–Landé model are calculated from the equilibrium condition and data of bulk modulus at room temperature. The computed values of pressure derivatives of bulk modulus at P=0 and the values of bulk modulus are found to be in very close agreement with experimental values for high-T _c copper oxide and their nonsuperconducting parent compounds. It is also found that the quantity U/U(V ₀) of these compounds increases with increasing hydrostistic pressure.     

Bi-Sr-Ca-Cu-O系高温超导体结构的电子显微镜研究

本文用透射电子显微术和 EDAX 对 Bi 系超导体的成份和晶体结构进行了分析研究。结果表明该 Bi 系超导体中存在 a=b=5.41(?)c=24.21(?)四方结构超导相,为改进成份、热处理工艺提供了依据。     

Primary Phase Field of the Pb-Doped 2223 High-Tc Superconductor in the (Bi,Pb)-Sr-Ca-Cu-O System

Both liquidus and subsolidus phase equilibrium data are of central importance for applications of high temperature superconductors in the (Bi, Pb)-Sr-Ca-Cu-O system, including material synthesis, melt processing and single crystal growth. The subsolidus equilibria of the 110 K high-T_c Pb-doped 2223 ([Bi, Pb], Sr, Ca, Cu) phase and the location of the primary phase field (crystallization field) have been determined in this study. For the quantitative determination of liquidus data, a wicking technique was developed to capture the melt for quantitative microchemical analysis. A total of 29 five-phase volumes that include the 2223 phase as a component was obtained. The initial melt compositions of these volumes range from a mole fraction of 7.3 % to 28.0 % for Bi, 11.3 % to 27.8 % for Sr, 1.2 % to 19.4 % for Pb, 9.8 % to 30.8 % for Ca, and 17.1 % to 47.0 % for Cu. Based on these data, the crystallization field for the 2223 phase was constructed using the convex hull technique. A section of this “volume” was obtained by holding two components of the composition at the median value, allowing projection on the other three axes to show the extent of the field.     

Software Techniques to Improve Data Reliability in Superconductor and Low-Resistance Measurements

Software techniques have been developed to take low-amplitude data in various patterns, assign a figure of merit to a set of data readings, edit data for erroneous readings (or other experimental variations), and to alert the experimenter if the detected errors are beyond the scope of the software. Erroneous voltage readings from digital voltmeters, intermittent electrical connections, and an array of similar variations in data have been detected through the use of a data editor. The fixed-limit data editor removes readings that are inconsistent with the distribution of the majority of the data readings. The frequency of erroneous readings from a particular digital voltmeter ranges from 1 error per 100 000 readings to 1 error per 100 readings. The magnitude of the error can be as large as 3% of full scale with a zero volt input to the voltmeter. It may be necessary to have multiple meters measuring voltages in the same circuit in order to generate these erroneous readings. A systematic study was performed on the occurrence of the internally-generated erroneous voltmeter readings, and it was determined that the amount that a reading was in error scaled with one of a few parameters. The software techniques described here have been used in a variety of measurements, such as resistance-versus-temperature measurements made on cryoconductors or superconductors, and voltage-versus-current measurements made on superconductors to determine the critical current.     

钢的高温硬度研究

测定了两组共13种工业用钢从室温到700℃的维氏硬度(H)。得出,具有平衡组织的碳钢,其 H—T 关系是非线性的,200—500℃,曲线出现平台,低碳钢甚至出现极大值;含碳0.2-1.2%的碳钢,随温度上升,硬度之差别逐渐减小,在700℃各钢硬度趋于一致;二次硬化状态的工具钢,在500℃以下 H-T 呈线性关系,提出了估算高速钢500℃以下硬度的简易公式;超过回火温度时,由于不可逆软化,使 H—T 关系成为非线性的。     

多芯复合超导线拉拔的有限元模拟

利用商业有限元软件DEFORM-3D对多芯复合超导线材的拉拔过程进行有限元模拟,研究变形过程中复合超导线各亚组元的变形情况,以及拉拔速度对超导线成形的影响.分析超导线拉拔过程中等效应力、等效应变的分布规律;并且结合韧性断裂准则来预测不同位置开裂产生的可能性.总结出拉拔速度对拉拔过程的影响规律,确定了拉拔过程中的危险区域.     

Static Theory of a Self-Driven Photo-Thermoelectrical High-Temperature Superconductor Bolometer

At the present time, radiation detection in the far infrared with millisecond response time requires use of complicated technology to obtain mK-degree operating temperatures and very high quality, critical temperature materials (e.g., W, Al). It is also customary to use films of nanometer thickness in the manufacture of such devices. In this paper, we present theory and computations for the performance a composite high-temperature superconductor (HTSC)–thermolectric materials bolometer, operated at 77 K and with films of thickness around 1 . A practical device with performance comparable to available photoelectrical bolometers is investigated. The simplicity of the technology involved makes it an attractive proposition. A semimetal film leg (SML; e.g., BiSb) is connected in parallel with a HTSC leg (HTSCL; e.g., YBCO). The bolometer is operated in a photovoltaic mode with no external source of bias power. The thermoelectric voltage developed across the SML leg due to radiation absorbed on the sensitive area of the bolometer remains shorted till there is a sufficient temperature rise of the HTSCL so that its resistance becomes comparable to that of the SML. The voltage thus developed across the bolometer would drive an external electronic readout circuit.     

Multimode Sapphire Resonator for the Measurement of Surface Resistance of HTS Films

A multimode sapphire resonator is developed for multiple frequency surface resistance measurement of a single piece of high-temperature superconductor thin film. Simple formulas are used for the calculations of surface resistances. On this sapphire resonator, three modes, TE_011+ε , TE_012+δ and TE_021+ξ (0<ε,δ,ξ<1), which had resonances at 11.84, 17.49 and 31.99 GHz were used simultaneously and the measured surface resistances at these frequencies were 0.553, 1.32 and 3.75 mΩ, respectively. The measured result matches the theory very well.     

Thermodynamic Properties of High-Temperature Superconductors in the Pseudogap Regime

Experimental data extracted from thermodynamic measurements in underdoped high-temperature superconductors show significant deviations from the results predicted by the BCS theory. In these particular compounds, the anomalies observed in the superconducting phase are associated also to the presence of a pseudogap in their normal state. On the basis of a simple model, which treats the pseudogap phenomenologically, we performed a Ginzburg–Landau expansion to extract the main properties of the superconducting phase. Our results for the specific-heat-coefficient jump at the transition point, (T _c), coherence length, T(T), and penetration depth, (T), qualitatively recover the experimental data.     

High-Temperature Oxidation Behavior of a Ni-Cr-W-Al Alloy

A study was conducted to examine the isothermal oxidation behavior of a new Ni-Cr-W-Al alloy in air at 1250℃ with different time. Oxidation kinetics was determined from weight-change measurements. The microstructure and composition of the oxide scale were investigated by means of scanning electron microcopy and X-ray diffraction. The results showed that the oxide scales of the alloy were a compact and continuous outer Cr2O3 and NiCr2O4 layer and an inner Al2O3 layer that was in dendrite shape. Oxides scales with good adherence were formed on the surface of the alloy, which made the alloy perform excellent high-temperature oxidation resistance.