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。     

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.     

片层法制备的NbTiTa/Cu超导体在3.0、4.2K的临界电流密度

将钛片、铌片和钽片在铜包套中按…TiTaNbTaTi…次序周期排列,通过4次挤压制成NbTiTa/Cu超导复合体,然后对复合体交替进行拉拔减径和时间分别为40、50、60、70h的时效热处理.在3.0、4.0K下随着最终附加应变的增加,NbTiTa/Cu超导线材的临界电流密度显著提高;在3.0 K、11T磁场中,1.25 mm直径线材的临界电流密度为350 A/mm2,表明采用片层法制备的NbTiTa/Cu超导线材具有高的上临界场.     

结合连续管线成型技术和粉末套管法制备SiC掺杂的MgB_2超导线材研究

结合连续管线成型技术和粉末套管方法,原位掺杂SiC制备出了20m长的单芯MgB2/Fe、MgB2/Nb/Fe线材和7芯、19芯及49芯的MgB2/Nb/Cu/Fe复合多芯线材。采用XRD和SEM分别对烧结后样品芯部进行相成分和微观结构研究,并通过TEM对SiC掺杂的机理进行了简单分析。采用四引线法对线材进行电流测量并获得临界电流密度。结果表明,线材经过不同温度保温15min的真空退火后,在800℃形成的MgB2相含量最高,其中单芯MgB2/Fe线材在4.2K,11T下Jc值超过104A/cm2,7芯复合线材在4.2K,7.5T下Jc值也达到104A/cm2,并且具有较好的热稳定性,在低场下仍可稳定通过电流。     

多芯MgB2超导线材的挤压制备技术及微观结构研究

为了提高多芯MgB2超导线材中芯丝相互之间的结合强度和超导芯丝的致密度,将传统的热挤压技术引入到MgB2线材制备过程中。采用挤压工艺制备180芯导体结构的多芯MgB2/Nb/Cu超导线材,Φ64mm的复合包套通过单道次挤压工艺加工到Φ20 mm。挤压后的线材通过冷拉拔和中间退火热处理最终加工到Φ0.81 mm。对加工不同阶段的复合线材进行了微观结构分析,发现多芯线材中MgB2超导芯丝分布良好,Nb阻隔层厚度分布较为均匀,无破损现象。通过该工艺已成功制备出百米量级长度的多芯MgB2超导线材。该技术为MgB2超导长线的制备提供了新途径。     

多芯MgB_2超导线材的挤压技术及其微观结构研究

为了提高多芯MgB_2超导线材中芯丝相互之间的结合强度和超导芯丝的致密度,将传统的热挤压技术引入到MgB_2线材制备过程中。采用挤压工艺制备180芯导体结构的多芯MgB_2/Nb/Cu超导线材,Φ64mm的复合包套通过单道次挤压工艺加工到Φ20 mm。挤压后的线材通过冷拉拔和中间退火热处理最终加工到Φ0.81 mm。对加工不同阶段的复合线材进行了微观结构分析,发现多芯线材中MgB_2超导芯丝分布良好,Nb阻隔层厚度分布较为均匀,无破损现象。通过该工艺已成功制备出百米量级长度的多芯MgB_2超导线材。该技术为MgB_2超导长线的制备提供了新途径。     

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。     

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。     

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。     

超导产业应用的未来展望

日本住友电工公司特别技术顾问中原恒雄在2000年7月大阪举行的超导科学技术研究会(FSST)第47次会议上作了《超导产业应用的未来展望》综述报告，现简述如下。长尺度Bi系线材 长尺度Bi系线材，宽约4mm，厚约0.2mm~0.3mm，长达约1000m，一天可制备数根，对这种线材每隔4mm进行连续测试评价。代表性的线材在77K，0T下的Ic约为74A。更详细地说，61芯Bi系线材，宽3.81mm，厚0.234mm，银比2.95，77K，0T下的Ic为74A，Jc为34kA/cm2，Je为8.1kA/cm2，是目前代表性的长尺度Bi系超导线材。高Ic Bi系线材 对设计稍作变动，可得更高Ic的Bi系线…     

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.     

高临界电流密度、低损耗Cu5Ni基NbTi线材制备技术研究

重离子装置中的加速器磁体均服役在±2.25T/s的高速脉冲条件下,因此要求该种磁体所用的超导线材具有较高的临界电流和较低的损耗。针对项目需求,本文设计及制备了两种新型结构的NbTi/Cu5Ni超导线材,芯数分别为12960芯和10800芯、铜比2.0、芯丝直径均小于5 μm。系统研究了两种新型结构超导线的芯丝截面形貌、芯丝表面形貌、磁滞损耗及不同时效热处理下的临界电流密度和n值。通过优化工艺后获得了Jc(5 T、4.2 K)为2902 A/mm_²,Qh(4.2 K,± 3T)为34.2 mJ/cm_³ 的千米级NbTi/Cu5Ni超导长线,并可实现批量化生产,为重离子装置的研制提供材料基础。     

通过Nb，Ti扩散反应制备不同成分的超导体

利用Nb片和Ti片交替组配加工,经扩散反应制备了Ti含量在42.56%-56.62%之间的3种不同成分的NbTi超导线。运用扫描电镜(SEM)观察了Nb/Ti界面的扩散形态及微结构,并对热处理工艺和不同Ti含量对临界电流密度(Jc)的影响进行了讨论。结果表明:随着Ti含量增加,可提高超导线在低场(<5T)时的临界电流密度Jc。该工艺制备的NbTi超导线材的Jc可达到2800A/mm2(5T,4.2K)和4200A/mm2(3T,4.2K)。随着Ti含量的增加,试样的Jc在低场时很高,而在高场时的性能偏低,且下降迅速,而Ti含量低的试样的Jc衰减相对缓慢些。对Ti含量较高的合金,在一定温度下,选用较短的热处理时间,可获得高的Jc,对Ti含最较低的合金,则要求较长热处理时间。     

Property of Amorphous/Nanocrystalline Hybrid Wires of TiNi-Base Shape Memory Alloys

The microstructures and mechanical properties of amorphous/nanocrystalline hybrid TiNi wires produced by severe cold drawing were investigated. Annealed wires of Ti-50.9?mol%Ni and Ti-41?mol%Ni-8.5?mol%Cu were subjected to severe cold drawing of 50-70% reduction. The as-drawn TiNi wires were composed of the mixture of amorphous phase and predominantly B2 nanocrystalline phase. Young??s modulus increased with the drawing reduction which can be attributed to the increase in the amount of amorphous phase. For the binary TiNi wires, the volume fraction of amorphous phase was estimated to be about 60% from Young??s modulus and electrical resistivity. The wires drawn over 60% exhibited peculiar large linear elastic strain which is quite different from superelasticity. Aging at 573?K led to an increase in tensile elongation as well as in the recoverable strain. The amorphization by cold drawing was also confirmed for Ti-41?mol%Ni-8.5?mol%Cu in 62% drawn wires.     

挤压过程中NbTiTa复合体的微观组织变化

研究了以Nb,Ti,Ta片为原料制备NbTiTa超导线材的工艺中各次挤压后NbTiTa复合体的微观组织以及复合体中各片层间的扩散行为.结果表明:挤压过程中复合体的温度升高和塑性变形造成的大量晶体缺陷使复合体中Nb,Ti,Ta片间发生了严重的互扩散.由于互扩散复合体中形成了非超导的富Ti区和超导的富Nb区和富Ta区,富Ti区的体积百分数超过30%,而且富Ti区、富Nb区和富Ta区的横界面在挤压和拉拔过程中都最终演变成了条带状.     

A metallurgical approach to high-Tc microcomposites

A metallurgical approach has been developed to produce high-critical-temperature (high-T_c) superconducting oxide/silver microcomposites. Metallic precursor alloys, which contain the metallic constituents of the superconducting oxides and silver, were made by melt spinning, melt dipping or melt writing, and then converted into superconducting microcomposites by atmospherecontrolled oxidation and annealing. The Bi-Pb-Sr-Ca-Cu-Ag alloy system was chosen as the system upon which to apply these methods, and superconducting composites with zero resistance at 104–110K and engineering critical current densities of 400–700 A/cm² at 77K were produced in this way with excellent reproducibility. The analysis of the process includes a variant of a temperature-time-transformation diagram. The processing methods discussed in this article have advantages in producing superconducting materials with improved mechanical properties and flexible shapes, including long ribbons, long wires and coils; they also can be used to join superconductors to either one another or normal metals.     

7芯复合包套Ba1-xKxFe2As2线带材的显微结构与超导性能研究

传统Ag包套与铁基超导材料具有良好的化学相容性以及塑性加工特性,但是其机械强度低;而采用复合包套来制备高强度Ba1-xKxFe2As2铁基多芯线带材是一种直接高效且成本低廉的方法。本研究选取高强度高延展性的Ag/Nb/Cu三层复合包套,从线带材包套尺寸、冷加工工艺和中间退火等方面进行优化,获得了结构稳定且易于加工的Ba1-xKxFe2As2多芯线带材。Ag/Nb/Cu复合包套Ba1-xKxFe2As2线带材的多芯孔型完整并且分布均匀,超导填充因子约为25.3-28.0%,并且具有较好的力学性能。Ba1-xKxFe2As2多芯带材的转变Tc为37.5 K,M-H曲线表明样品具有较强的内在磁通钉扎能力。在4.2 K和2 T下其传输Jc约为1.0×104 A/cm2,在10 T时传输Jc仍然保持为8.7×103 A/cm2。     

Mechanical properties of molybdenum products prepared by using molybdenum powders with different micro-morphologies

Using two kinds of molybdenum(Mo) powders with different micro-morphologies as raw materials, the Mo wires with a diameter of 0.18 mm and Mo sheets with thickness of 0.5 and 0.2 mm were prepared at the same process of pressing, sintering, drawing, or rolling, respectively. By comparative analysis on the microstructure and mechanical properties of Mo wires and Mo sheets, the effect of Mo powder micro-morphology on properties and quality of Mo products was studied. The results show that,compared with that prepared by traditional Mo powder with inhomogeneous particle size and aggregation, the Mo wires prepared by specific Mo powder with homogeneous particle sizes, less agglomeration, and better dispersion exhibit higher yield, higher tensile strength, and lower elongation at room temperature, and the Mo sheets also show excellent high-temperature performances and better isotropy. The essential reason for those is the difference of Mo powder micro-morphology. Inhomogeneous particle size and aggregation of Mo powder greatly influence the microstructure of Mo sintered compacts and mechanical properties of Mo products.     

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.     

TiC掺杂12芯MgB2线材微观结构以及超导电性

采用 PIT工艺,以分步法粉末为装管前驱粉,选用中心铜铌复合棒增强的导体结构制备了TiC掺杂MgB2多芯线材,研究了不同热处理温度对于粉末相组成、线材的微观结构以及超导电性的影响,结果表明分步法粉末能够有效提高C原子的取代水平,同时芯丝中MgB2晶粒尺寸达到亚微米级,MgB2晶粒连结性较好,制备多芯线材在4.2 K,5 T时,其Jc仍高达3×104 A/cm2。