尺寸条件下Cu-Nb-Cu复合线材微观结构的演变机制

本文采用集束拉拔技术成功制备出了Nb管增强Cu-Nb的多芯复合线材,分别对不同尺寸(Φ2.5mm、Φ2.2mm、Φ2.0mm,Φ1.7mm)线材的微观形貌进行了表征,并测试了不同尺寸线材的纳米压痕实验曲线.探究了尺寸效应下,Cu-Nb-Cu复合线材微观形貌的变化规律,及引入Nb管后,材料的界面、芯丝、及不同铜层的硬度演变规律.最后通过对Φ1.7mm线材进行高分辨场TEM测试,结果显示,线材经过大塑型变形后,完整的Nb管已经发生了破裂,呈条带状分布.     

氧化石墨烯增强Cu-Nb 复合线材结构及性能影响研究

本文采用粉末套管法成功制备出氧化石墨烯增强的 GO/Cu-Nb 多芯(192 芯) 复合线材及未掺杂氧化石墨烯的 Cu-Nb 多芯(192 芯) 复合线材. 通过金相、SEM 及拉曼光谱等表征不同尺寸下两种复合线材的芯丝组态、 界面特征及特征峰. 结果表明, 氧化石墨烯由于良好的自润滑特性较好地协调了芯丝与基体的变形, 其弥散分布有效阻隔了 Nb 颗粒团聚及大尺寸晶粒的产生, 芯丝变形更均匀, 形态更规则. 力学和电学性能测试结果表明, 掺杂氧化石墨烯后,Cu-Nb 复合线材的力学与电学性能均明显提升, 分析认为, 氧化石墨烯的尺寸大小、 分散均匀性及热处理是影响线材综合性能提升的主要原因.     

变形方式对Cu-Nb复合线材的结构和性能影响研究

Cu-Nb复合线材作为一种典型的高强度、高电导、高导热铜基复合材料,是制备超高场脉冲磁体的首选导体材料.低温和轧制变形作为梯度纳米材料塑性变形的新型变形手段,得到广泛关注。本文分别开展了低温、轧制变形方式对锯管增强Cu-Nb复合线材(Cu-Nb-Cu)的结构及性能影响的研究.有效调控了复合线材的强度和电导倒置关系,实现了Cu-Nb-Cu复合线材的综合性能突破.揭示了轧制变形后Cu-Nb-Cu复合带材的芯丝结构演变特征,探讨了Cu-Nb-Cu复合线带材的低温和轧制变形机理.     

Nb芯增强MgB2多芯超导线材的制备及性能研究

以Nb/Cu复合管作为外包套材料,Nb棒作为中心增强体,通过原位法粉末装管工艺(in-situ PIT)制备了不同芯丝结构的TiC 粉末掺杂MgB2/NbCu多芯线材.在高纯流动氩气保护条件下、700℃烧结2h进行成相反应.对烧结后的线材分别进行了应力-应变分析、微观结构以及超导电性等分析检测.拉伸实验分析表明,Nb芯...     

千米量级多芯MgB2/Nb/Cu超导线材的制备及性能研究

以无磁性的Nb作为中心增强体和阻隔层材料,无氧铜作为稳定体包套材料,采用原位法粉末装管工艺(in-situ PIT)制备了千米量级7芯导体结构的MgB2/Nb/Cu超导线带材,由于Nb/Cu包套材料具有良好的塑形加工性能,整个加工过程中未进行中间退火热处理,复合多芯线材最终加工到Φ1.4mm;在真空热处理炉中680℃保温2小时进行成相热处理;对烧结后的线材进行了微观结构、超导电性、纵向电流分布均匀性及常温力学性能等分析检测.线带材的工程临界电流密度在20K,1T磁场条件下达到2.5×104 A/cm2.结果表明该工艺能够制备实用化高性能的MgB2线带材.     

Nb芯增强千米级7芯MgB_2超导线材的机械性能及超导性能研究

以非铁磁性的Nb作为中心增强体和阻隔层材料,无氧铜作为稳定体包套材料,采用原位法粉末装管工艺(in-situ PIT)制备了千米量级6+1芯导体结构的MgB2/Nb/Cu超导线带材,由于Nb/Cu包套材料具有良好的塑形加工性能,整个加工过程中未进行中间退火热处理,复合多芯线材最终加工到Φ1.4mm;在真空热处理炉中680℃保温2小时进行成相热处理;对烧结后的线材进行了超导电性、纵向电流分布均匀性及弯曲及拉伸力学性能等分析检测。线材的工程临界电流密度在20K,1T磁场条件下达到2.5×104A/cm2,表明该工艺能够制备实用化高性能的MgB2线带材。     

MgB_2/Nb/Cu多芯线材的力学性能研究

实验中对采用原位法粉末装管工艺(in-situ PIT)制备的Nb芯增强,6芯、12芯和36芯等多种导体结构的Nb/Cu复合包套MgB2多芯超导线材的力学性能进行了针对性地研究;设计并加工了一套专门用于低温下MgB2线带材弯曲应力测试的样品架;研究了MgB2线带材的临界电流随弯曲应力的变化性能;同时研究了室温及低温条件下的拉伸对MgB2线材超导电性的影响。力学性能分析表明,所制备的Nb芯增强6芯MgB2超导线材在弯曲直径为80mm以上时,超导临界传输电流没有出现明显的退降,同时该线材的拉伸力学性能也比未增强线材有明显的改善。     

有限元法模拟Nb_3Sn线材的应变分布

Nb3Sn超导磁体正常运行时,复合超导线材将受到大的机械载荷(如温度载荷、轴向拉伸和电磁力),其超导电性可能发生可逆和不可逆的退化。针对Nb3Sn线材经高温热处理后冷却到4.2K所产生的热应变,对复合线材结构建立详细的三维有限元分析模型,解决了一维模型不能详细模拟应变分布的问题,从微观尺度仿真了导体内部的应变分布,阐明了导体不同组份材料上热应变分布的特点。在此基础上,进一步分析了对Nb3Sn复合导线施加轴向拉力时,内部Nb3Sn芯丝上由压应变向拉伸应变的转换过程。     

尺寸对Cu-Nb微观复合材料磁滞特性的影响

本文研究了Cu-Nb多芯复合线微观结构对磁滞特性的影响.样品通过不同塑性应变和热处理获得不同显微结构.结果表明,经冷加工变形和800℃/1.5h退火,尺寸为Φ1.06mm样品的磁化曲线中只在高场下出现了一个峰,这个峰来源于Nb的体钉扎.Φ2.04mm样品在退火后的曲线中出现了三峰结构,低场下的两个峰是由于临界效应使Cu基体中产生了超导电性引起的,而高场下出现的第三个峰也与Nb的体钉扎有关.样品中Nb芯丝直径及芯丝间距等因素影响了复合材料直流磁化曲线的特征.     

热处理对C掺杂MgB2/Nb/Cu单芯线材微观结构及超导电性的影响

采用原位法粉末装管工艺(In-situ)制备了MgB2/Nb/Cu单芯线材,通过X射线衍射(XRD)、能谱分析(EDS)和物性测试仪(PPMS)等手段研究了热处理温度对线材微观结构及超导电性的影响.结果显示,随着热处理温度的提高,衍射图谱中的(110)峰向高角度偏移,说明掺杂元素C进入晶格的量也在增加;烧结温度对C掺杂...     

高性能内锡法Nb_3Sn超导股线生产用Sn-Ti合金的研制

高性能内锡法Nb3Sn超导股线可用于国际热核聚变反应堆(ITER)磁体,股线加工过程中的断线问题是股线制备的关键技术之一.在股线的Sn组元中添加适量的Ti不但能够提高Sn的强度利于股线的长线加工;同时Ti元素的添加还可以提高热处理中Nb3Sn的成相速度,降低晶粒尺寸,提高股线的电磁特性.本文介绍了满足Nb3Sn超导股线制备要求的Sn-Ti合金的制备技术,分析了不同浇铸温度对铸锭的影响,对比了加工中Sn-Ti合金的微观组织变化,为我们制备满足ITER要求的Nb3Sn超导股线提供了重要的保障.     

Effect of dislocation hardening on monotonic and cyclic strength of severely deformed copper

The present study aims at clarifying the role of dislocation strengthening in fatigue of materials manufactured by severe plastic deformation (SPD) techniques. Employment of single crystals hardened via equal channel angular pressing (ECAP) helps to minimise or completely eliminate the effect of high angle boundaries on strengthening and fatigue behaviour. Both monotonic strength and high cycle fatigue (HCF) resistance were improved significantly after the first ECAP pressing, when low-angle dislocation configurations dominate in the microstructure. The essential role of dislocation accumulation during severe plastic deformation is highlighted for both tensile and fatigue strength (SPD). Dilute alloying of copper by silver stabilises the deformation microstructure and further improves the fatigue properties considerably.     

Intensification of tube drawing by axial ultrasonic oscillation of the plug

During tube drawing with axial ultrasonic oscillation of the plug at high intensities, a dynamic force occurs, the magnitude of which is comparable with the forces of plastic deformation of metallic materials. Significant reduction in the drawing force is then obtained with the possibility of intensification of the drawing process, especially for metals and alloys with low deformability. It has also been observed that, for constant oscillation amplitude of the plug, the reduction in the drawing force decreases with increasing drawing velocity.     

Influence of heat treatment on microstructure and mechanical properties of the interface in an EN AW-6082/1.4310 composite extrusion

The presented paper deals with a unidirectional steel wire reinforced aluminum matrix composite manufactured by composite extrusion. The main objective of this work was to determine the effect of heat treatment, and the influence of long solution annealing times on the composites interface regarding microstructural changes and the resulting interface strength. For evaluation of the microstructure high resolution transmission electron microscope (TEM) investigations accompanied with electron dispersive X-ray spectroscopy (EDX) were performed. It could be shown that diffusion from the steel wire into the aluminum matrix occurs and that the diffusion paths as well as particle formation is influenced by the preceded heat treatment. Diffusion paths in the range of 40–150 nm could be observed for Al, Fe, Cr and Ni. After annealing times over 5 h an extensive growth of an intermetallic reaction layer was found. The mechanical properties of the interface were determined by push-out-tests and tensile tests radial to the interface, which provided the debonding shear strength σ_deb and for the latter experiment the interfacial radial strength σ_IR. It has become apparent that debonding shear strength is highly influenced by matrix properties. In radial tensile tests the failure is predominantly controlled by the chemical bond of the interface. It was shown that interface strength of specimen with small reaction zones of about 3 μm were beneficial for the mechanical behavior in both loading conditions. Longer annealing times showed a drastic decrease of interface shear strength. It was concluded from EDX measurements and in comparison with literature that the reaction zone is dominated by the growth of Al₅Fe₂ (η-phase).     

颗粒增强金属基复合材料变形强化中的应变梯度效应

 针对单轴压缩实验,根据颗粒增强金属基复合材料中颗粒和基体两相的局部变形协调条件,并通过简单的位错模型,确定出与变形协调相应的几何必需位错密度,进而导出一种颗粒强化-应变梯度律。从中可以清楚地看出,颗粒增强金属基复合材料的强化由材料的微结构特征几何参数l和基体应变梯度联合控制。对于颗粒含量一定的复合材料,颗粒越小,应变梯度越高,强化效果越好。这一结果揭示了,颗粒强化及尺寸效应主要是通过应变梯度效应来表现的。这也同时说明,应变梯度可能是控制材料变形与断裂的重要因素之一。     

Effect of laser melting on plasma-sprayed aluminum oxide coatings reinforced with carbon nanotubes

The effect of laser melting on the microstructure and mechanical properties of plasma-sprayed aluminum oxide composite coating reinforced with 4 wt% multi-walled carbon nanotubes (CNTs) is reported. Laser-melted layer consists of dense, coarse columnar microstructure which is significantly different from plasma-sprayed coating that consists of splats and porosity. CNTs retained their original cylindrical graphitic structure after undergoing laser irradiation. Three dimensional heat flow model has been developed to estimate temperature variation in the laser-melted composite layer. Laser-melted layers show an increase in the microhardness at the expanse of degradation of fracture toughness. Nanoindentation study indicates an increase in the elastic modulus and yield strength of the laser-melted layer which is attributed to dense microstructure with absence of weak-bonding splats and porosity.     

超细Ni80Cr20合金丝的冷拉拔制备及表征

开展特定直径超细Ni80Cr20合金丝的冷拉拔制备研究,并通过扫描电子显微镜(SEM)、X射线衍射仪(XRD)和金属丝强力仪等对超细合金丝进行了表征。研究结果表明:烧头过程最佳电解液浓度为0.05mol/L,时间为3s;制备的镍铬合金丝直径为24.54μm,表面光滑,尺寸精准;拉拔后晶粒尺寸减小,退火后晶粒尺寸长大;拉拔态镍铬丝由于加工硬化,其伸长率由16%降低至1.88%;退火可改善镍铬丝性能,其断裂强度降低,伸长率增大,合金塑性增强,氮气退火丝的断裂强度大于真空退火丝的断裂强度,伸长率则相反。