原位粉末装管法37芯MgB2线材的制备及性能研究

传统的Cu包套原位粉末装管法(in situ PIT)制备多芯MgB₂超导线材时,易于出现断芯、断线现象。针对一问题,本实验中以强度较高的梦乃尔合金(Monel 400)作为包套材料,以旋锻、拉拔、轧制及中间热处理相结合的加工手段成功的制备出直径Φ1.0 mm、37芯结构的多芯MgB₂超导长线材。微观结构分析表明多芯线材中MgB₂芯丝及替换芯丝等亚组元的分布较为规整,阻隔层未出现明显破损现象,最终线材中MgB₂超导芯丝的平均直径约80 μm。室温拉伸性能显示热处理前MgB₂线材的屈服强度为759 MPa,热处理后的线材为248 MPa。4.2 K、4 T下,线材的临界电流密度J_c达到2.31×10^₅ A.cm^_-2,工程临界电流密度达到3.16×10^₄ A.cm^_-2。     

19芯MgB2/NbCu/Monel超导线材的制备及性能研究

为了提高多芯MgB₂超导线材的强度并避免加工过程中的断芯、断线现象,实验中采用强度较高的梦乃尔合金(Monel 400)作为外包套材料,以原位法粉末装管工艺(in situ PIT)制备了19芯导体结构的多芯MgB₂超导线材。二次集束组装后的多芯复合线材通过拉拔、轧制和中间退火热处理相结合的方法从Φ25 mm加工到Φ1.0 mm。对加工过程不同阶段的多芯复合线材进行了微观结构分析,发现多芯线材中MgB₂芯丝分布较为规整,Nb阻隔层表面较为光滑,未出现明显破损现象。最终Φ1.0 mm的多芯线材中MgB₂超导芯丝的平均直径约为100 μm。热处理后MgB₂线材的抗拉强度和屈服强度分别达到396 MPa和200 MPa。MgB₂线材的临界电流密度在4.2 K、4 T时达到1.23×10₅ A.cm_-2。     

高临界电流密度NbTiTa/Cu超导线材

将Nb片、Ti片、Ta片在Cu包套中按照周期的次序…TiTaNbTaTi…排列,然后通过真空焊封、热等静压、热挤压制成61芯NbTiTa/Cu复合体,对复合体在700、600、500℃进行扩散热处理,最后进行减径加工得到φ0.2 mm的NbTiTa/Cu超导线材.在500℃扩散处理后,61芯NbTiTa/Cu超导线材在4.2K的临界电流密度(磁场强度)为5290.29 A/mm2(3T),3782.14 A/mm2(4T),2865.8 A/mm2(5T),1882.65A/mm2(6T),达到国外传统工艺NbTiTa/Cu超导线材临界电流密度的较高水平.在600℃扩散处理的NbTiTa/Cu超导线材的临界电流密度很低,主要是由于扩散温度高,芯丝的成分趋于均匀,从而缺乏α-Ti磁通钉扎中心所致.     

中心Mg扩散工艺6+1芯MgB2线材的制备及其性能

采用中心Mg扩散工艺(IMD)设计并成功制备了2种不同导体结构(Cu和CuNb芯)的百米级MgB₂线材，分别测试了线材的力学性能和超导传输性能；超导层临界电流密度(Layer Jc)达到4.3×105A/cm2(4.2K,4T)。采用不同方法分析了2根线材纵向MgB₂超导层分布的均匀性，发现随着线材直径的减小，超导层分布更趋于均匀化，Φ0.8mm的线材基超比波动范围最小，基超比极差为0.02;MgB₂层分布均匀性的研究显示该线材中Mg、B密度分布均匀性良好；超导电性的测试结果显示Cu替换芯线材临界电流Ic比CuNb替换芯线材临界电流Ic高出19A(4.2K,4T)，而Jc性能基本一致；相同磁场强度下Cu替换芯线材载流均匀性与稳定性(n)均高于CuNb替换芯线材n值。该研究结果表明IMD工艺制备的MgB₂线材能应用于绕制小型磁体以及Mg/B/Nb/Monel基体能够开发百米级高性能的MgB₂线材。     

ITER用NbTi超导线材微观组织及性能

本研究以国际热核聚变反应堆(International Thermonuclear Experimental Reactor,ITER)磁体极向场用NbTi超导线材的性能优化为目的,通过TEM研究热处理工艺对NbTi超导线材微观组织及4.2 K温度下临界电流的影响.结果表明,具有高Jc值的NbTi在4.2 K条件下析出具有典型形貌的α-Ti钉扎中心,即弥散分布于β-NbTi基体上,高度褶皱及卷曲.较高温度的热处理有利于4.2 K下Jc的提高,但增加热处理次数使Jc值略微降低.     

轧制与拉伸对NbTiTa/Cu多芯复合线超导性能的影响

利用Nb47Ti和Ta片作为原料,经过3次挤压并结合拉伸和轧制2种不同工艺,通过时效热处理制备出了NbTiTa/Cu超导线材.通过标准四引线法测量了2种线材在4.2 K下的超导性能.结果表明,采用拉伸法制备的NbTiTa线材具有更高的临界电流密度,φ1.0 mm的超导线材Jc在4.2 K、8 T下,超导性能达到791 A/mm2.通过对线材的微观组织观察表明:在相同条件下,采用拉伸后的试样芯径大小均匀、铜比均匀、芯丝排列整齐且间距相等.     

芯丝中Ta分布对NbTiTa超导线材性能的影响

用Nb47Ti片和Ta片制备NbTiTa/Cu超导线材,在三次热挤压和热处理后NbTiTa超导线材的芯丝中Ta成豆状和条带状,Ta和Nb47Ti间的互扩散很小。在NbTiTa超导芯丝中α-Ti钉扎中心成条带状,厚度为5～10nm,间距为20～50nm,讨论了α-Ti钉扎中心的尺寸和间距对磁通钉扎效果的影响。结果表明,当温度降到3.0K时NbTiTa/Cu超导线材在高场中的临界电流密度反映出Ta在芯丝中作为非超导相依然能够起到提高线材的上临界场和高场中临界电流密度的作用。不同直径的NbTiTa/Cu超导线材的临界电流密度表明,较大的最终附加应变对临界电流密度的提高具有重要意义,如果进一步减小线材的直径,线材的临界电流密度可以继续提高。     

DEFORMATION BEHAVIOR OF SPRAY–DEPOSITED La–BASED BULK AMORPHOUS ALLOY IN SUPERCOOLED LIQUID REGION

研究了喷射成形大尺寸La₆₂Al_15.7(Cu, Ni)_22.3非晶合金在过冷液相区内的塑性变形行为. 结果表明, 随加热温度 的增加和应变速率的减小, 该非晶合金由非稳态变形向单一稳态变形行为转变. 当应变速率为5×10^-3 s^-1, 温度为443 K和挤压比为6.25时, 喷射成形La₆₂Al_15.7(Cu, Ni)_22.3非晶合金样品的密度由挤压前的5.723增加到挤压后的5.924 g/cm³, 达到了同成分吸铸态非晶合金密度 (6.134 g/cm³) 的96.6%. 挤压后非晶合金样品依然保持完全非晶态.     

喷雾热分解制备Bi-2212前驱粉末的相演变和超导性能

采用喷雾热分解技术制备高温超导Bi₂Sr₂CaCu₂O_x（Bi-2212）前驱粉末,并研究了粉末热处理过程中的相演变过程及线材的超导性能。结果表明,喷雾热分解制备的粉末平均粒度为3.03 μm,颗粒为球状并呈弥散分布。粉末在热处理过程中的相演变包含4个过程：粉末在527 ℃下主要进行硝酸盐的分解和组元之间的初步反应;由于喷雾粉末具有很高的活性,在588 ℃时生成Bi₂Sr₂CuO_x（Bi-2201）相;喷雾粉末在780 ℃发生Bi-2212相的成相反应;在834 ℃时粉末完全融化。Bi-2212/Ag超导线材的热处理温度窗口很窄,最高热处理温度T_max变化±2 ℃时,临界电流I_c的降幅达到了31 A。Bi-2212/Ag超导线材的最佳T_max为885 ℃,在该温度条件下制得的线材临界电流I_c（4.2 K, 0 T）达到最高值,约为486 A。前驱粉末的热处理气氛为氧气时,线材的临界电流可以进一步提高到712 A。     

热处理制度对MRI用低铜比NbTi超导线材临界电流密度的影响

以高均匀性Nb47Ti合金锭和高纯无氧铜为原材料,制备了低铜比(1.3)的MRI(Magnetic Resonance Imaging)用NbTi/Cu超导线。研究了时效次数、时效时间和Nb47Ti棒材对NbTi/Cu超导线临界电流密度的影响。测试结果表明:时效次数(3次)相同时,时效时间从120 h延长到200h,临界电流密度基本无变化。时效4次后的临界电流密度较时效3次后大约提高234 A/mm2(4.2 K,5 T),而时效4次和5次后的临界电流密度基本相同。经工艺优化后,时效次数为4次或5次时临界电流密度最高,为3158~3161A/mm2(4.2 K,5 T,判据0.1μV/cm)。     

涡流检测在制备NbTi/Cu六方单芯棒中的应用

利用涡流检测技术可以检测NbTi/Cu六方单芯棒表面铜层中的缺陷。采用外穿过式差动线圈检测方法,对NbTi/Cu六方单芯棒实现涡流探伤。结果表明,涡流检测方法能够有效检测出六方单芯棒表面铜层中存在的夹杂、面上压伤及磕伤等缺陷,保证了单芯棒的质量。涡流检测方法有利于控制超导线材的质量。     

Fabricating Ag2O-stabilized superconductive wires

Fabrication of metal-shielded YBa₂Cu₃O_x superconductive wires provides a possible route to improve the poor mechanical properties and the low critical current densities associated with the ceramic nature of high-T_c superconductive oxide materials. However, results show that wires produced by the powder-in-tube method have low critical current densities and a wide superconducting transition range. A possible reason for these phenomena is the presence of a considerable amount of oxygen-deficient phase in the wire core due to insufficient oxygen diffusion through the metallic shield in the final annealing process. Silver oxide (Ag₂O) was introduced as an in-situ oxygen donor to stabilize the oxygen stoichiometry of the core material. Traditional powder and mechanical metallurgy methods have been used to fabricate these metal-shielded YBa₂Cu₃O_x superconductive wires for bulk electricity applications.     

Transport properties of sealed MgB2/Fe/Ni multifilamentary wires heat treated in air

Ni sheathed multifilamentary MgB₂ wires with Fe barrier and Cu stabilizer were prepared by the in situ Powder-In-Tube (PIT) method. After rolling, the ends of the wires were sealed by a simple capping technique and the wires were directly heat treated in air, without vacuum or any inert atmosphere. The quality of the wires was assessed by analysing the phase assemblage and measurement of superconducting properties such as R-T, J_C-T and J_C-H. Phase analysis revealed that only traces of MgO was formed in the superconductor core. Typical multifilamentary wires prepared by this method showed a T_C ≈ 38.5 K and ΔT_C ≈ 1 K and J_C of the order of 10⁵ A/cm² at 6 K (0 T) and 10⁴ A/cm² at 4.2 K (6 T) respectively. These values are quite comparable with the values obtained for wires heat treated in inert atmosphere.     

First-principles Study on Structure and Hardness of the RuB2

采用原位法粉末装管工艺( in-situ PIT)制备了无定形碳掺杂MgB2/Nb/Cu超导线材并研究了该掺杂对MgB2微观结构及超导电性的影响.复合线材中以Nb作为阻隔层、Cu作为稳定体并采用冷拉拔工艺进行加工.研究了无定形碳掺杂对MgB2相形成、微观结构及超导电性的影响,其中掺杂量分别为MgB2-xCx(x=0.0,0.05,0.08,0.10,0.15).分别采用XRD、SQUID、SEM/EDS及传输电流测试等方法对MgB2/Nb/Cu线材进行分析测试.XRD分析结果显示,700℃热处理后的线材可以获得纯度较高的MgB2超导相;微观结果照片显示无定形碳掺杂后可以获得良好的晶粒连接性;能谱分析表明掺杂物C元素均匀的分布在MgB2基体中;通过四引线法测试了传输临界电流密度Jc,在4.2 K、5T,其Jc值高达1.4×105 A/cm2;在4.2K、10T,其Jc值为3.3×104A/cm2.     

Niobium aluminide as a source of high-current superconductors

The development of high-critical-current superconducting A15 conductors able to carry current in very high magnetic fields (25–30 T) is recognised as an enabling technology for the construction of second-generation NMR magnets operating at frequencies well above 1 GHz. This paper highlights the current status of development of the niobium-aluminide intermetallics with special attention to Nb₃Al, and Nb₃(Al_1-x,Ge_x). Discussion is focused on the materials science aspects of conductor manufacture, such as β-phase (A15) formation, with particular emphasis on the maximisation of the superconducting parameters, such as critical current density, J_c, critical temperature, T_c, and upper critical field, H_c2. Many successful manufacturing techniques of the potential niobium-aluminide intermetallic superconducting conductors, such as solid-state processing, liquid-solid processing, rapid heating/cooling processes, are described, compared and assessed. Special emphasis has been laid on conditions under which the J_c(B) peak effect occurs in some of the Nb₃Al wires. The case is made that mechanical alloying during final wire preparation plays an important role in diminishing the peak effect, except in the case of A15 formation from a mixture of ‘σ-phase’ and Nb. Further study of the influence of mechanical alloying on the maximisation of the critical current density at high magnetic fields is crucial to the understanding of the peak effect formation in tapes formed from ‘σ-phase’. Additionally, many aspects of conductor design requirements such as stress, strain, a.c. losses, thermal and electromagnetic stabilisation, are discussed with reference to literature sources.     

Superconductivity research and applications development at IGC

Intermagnetics General Corporation’s experience in producing high-quality metallic (NbTi and Nb₃Sn superconducting wires, tape, and cable provided the foundation on which it developed a process for manufacturing high-critical-transition-temperature superconductors. The product with the greatest near-term potential is silver-sheathed (Bi, Pb)₂Sr₂Ca₂Cu₃O_x, which is produced by the powder-in-tube process.     

Coextrusion of superconducting wires

Cu/Y₁Ba₂Cu₃O_7?x superconducting composite wires have been fabricated using the powder-in-tube coextrusion process. Increase in load during the extrusion process seems to indicate that powder particles from the deformation zone of the die travel up toward the unextruded part of the billet and gradually increase the density in that part to some saturation value, which prohibits further extrusion at moderate to heavy applied load. A powder removal technique has been devised to perform full length extrusion under such conditions. Powder removal, however, is not required if the extrusion ratio is reduced sufficiently. The extrusion ratio that will give a full length extrusion without powder removal seems to be a function of starting billet length. Extrusion ratio of 2.52 gives smooth full length extrusions with 25.4 mm (1 in.) starting billet length at reasonable load values. Four probe resistivity and magnetic susceptibility measurements indicate a critical temperature (Tc) value of the formed wire to be close to 88 K. Density measurements using the volume displacement method indicate a value of 4.819 g/cm³, which is approximately 76.5% of the theoretical density. M.M. Dehghani and A. Ahmad are Assistant Professor and     

NbTi合金的主要缺陷及形成机制

通过对Nb Ti超导线材的制备过程中引起断线的典型缺陷表征,分析了Nb Ti合金中加工流线的形成和溶质再分配导致的富Ti偏析现象以及流线和暗斑的形成机理。结果表明:Nb Ti合金中的富Ti偏析可用X-Ray透射照片中的呈现的黑斑和木纹表征,其实质是一种通道偏析,为后续改进Nb Ti合金制备工艺,消除富Ti偏析、提高Nb Ti合金成分以及组织均匀性奠定基础。     

Experimental investigation and Ginzburg–Landau modeling of the microstructure dependence of superconductivity in Cu–Ag–Nb wires

The type-II superconducting properties of heavily deformed Cu–Ag–Nb wires, containing only 4 wt% (4.18 vol.%) of elongated Nb filaments as a separate superconducting phase, were investigated as a function of microstructure, temperature, total wire strain, and external magnetic fields. The microstructure of the wires was examined using optical and electron microscopy. The experimental observation of the proximity effect, i.e. of the penetration of the superconducting state into the normal resistive Cu–Ag matrix leading to bulk-superconductivity, is explained in terms of the experimentally determined topology of the microstructure in conjunction with Ginzburg–Landau theory. The pronounced drop of the critical temperature and of the critical magnetic field with increasing wire strain is explained in terms of the reduced thickness of the ductile Nb filaments which is at large strains of the order of the Ginzburg–Landau correlation length in Nb.