处理电流密度对钴基非晶薄带巨磁阻抗效应的影响

本文研究了焦耳处理工艺的处理电流密度对Co68.15Fe4.35Si12.5B15和Co71．8Fe4．9Nb0.8Si7．5B15非晶薄带巨磁阻抗效应的影响。样品在不同电流密度下进行了处理。实验结果表明：焦耳处理存在最佳电流密度,对Co68.15Fe4.35Si12.5B15窄带来说,最佳处理电流密度为30A／mm^2,处理后样品的阻抗变化率峰值和灵敏度分别为119％和73％／Oe;对Co71．8Fe4．9Nb0.8Si7．5B15窄带来说,最佳处理电流密度为35A／mm^2,处理后的阻抗变化率峰值为232％,灵敏度在30A／mm^2时达到42％／Oe。处理后样品的内应力得到有效释放,软磁性能提高,使薄带的巨磁阻抗效应较淬态时有了明显提高。处理电流密度是焦耳处理方法中影响钴基非晶薄带巨磁阻抗效应的一个重要参数。     

低频脉冲电流退火对CoFeSiB非晶薄带巨磁阻抗效应的影响

研究了经不同低频脉冲电流密度退火的Co66.3Fe3．7Si12B18非晶薄带的巨磁阻抗（GMI）效应。结果表明，在低频脉冲电流下，巨磁阻抗效应的大小与退火电流密度密切相关。非晶带的GMI变化率△Z／Z先随退火电流密度的增加而增强，当电流密度为104A／mm^2时，△Z／Z达到最大值53．8％，此后随电流密度增大，GMI变化率开始减小。对脉冲电流退火影响巨磁阻抗效应的机制作了定性分析。并分析了由脉冲电流退火在材料内感生的横向各向异性场凤对GMI效应的影响，发现HK有利于提高GMI效应的峰值，但同时存在一个临界值，当超过这个值时，GMI效应的峰值减弱。     

磁场退火对CoFeNiNbSiB薄带巨磁阻抗的影响

本文研究了磁场退火对CoFeNiNbSiB非晶薄带巨磁阻抗（GMI）效应的影响，样品在不同条件下进行了退火热处理，结果表明，在300℃下经横向磁场退火处理后获得了最佳的软磁特性，从而得到了最大的GMI效应，在800KHz的交变电流频率下，得到了236%的最大磁阻抗比，在低场下，材料的磁阻抗磁场灵敏度达到1152%/mT。     

脉冲电流退火对Fe73.5Cu1Nb3Si13.5B9合金薄带巨应力阻抗效应的影响

研究了脉冲电流退火工艺对非晶Fe73.5Cu1Nb3Si13.5B9合金薄带巨应力阻抗（GSI）效应的影响。结果表明，在外加100MPa拉应力下对非晶合金进行脉冲电流退火后，巨应力阻抗效应显著提高，并且△Z／Z最大值随退火电流密度的增加而增加，当退火电流密度为930A／mm^2时，阻抗的最大相对变化达到350％。     

退火工艺对Co71．8Fe4．9Nb0．8Si7．5815非晶薄带巨磁阻抗效应的影响

采用四端法研究了退火处理T艺对Co71.8Fe4.9Nb0.8Si7.5B15非晶薄带巨磁阻抗效应的影响.结果表明,Co71.8Fe4.9Nb0.8Si7.5B15非晶薄带试样经350 ℃保温60 min退火处理后,样品的内应力得到有效释放,大大改善了样品的软磁特性,得到了最大的巨磁阻抗效应(GMI).在8 MHz的交变电流频率下,得到了24%的最大磁阻抗比.XRD分析表明,样品发生晶化后将降低巨磁阻抗(GMI)效应.     

Fe73.5Cu1Nb3Si13.5B9非晶丝扭矩阻抗（TGI）效应的研究

本文研究了测量频率、焦耳退火处理及扭矩焦耳退火处理对Fe73.5Cu1Nb3Si13.5B9非晶丝TGI效应的影响。实验表明淬态Fe73.5Cu1Nb3Si13.5B9非晶丝TGI效应的最佳测量频率为7 MHz;对样品进行焦耳退火处理可以提高样品的阻抗变化率,测量频率为7 MHz时,焦耳退火处理的最佳电流密度为32 A/mm2,最大阻抗变化率达198%;扭矩焦耳退火处理后,样品TGI效应的非对称性随着预加扭矩的增大而增大,同时阻抗变化率峰值减小。     

脉冲电流处理对Fe73.5Cu1Nb3Si13.5B9合金薄带GMI效应的影响

本文研究了脉冲电流处理对Fe73.5Cu1Nb3Si13.5B9合金薄带巨磁阻抗效应和脆性的影响,并与等温退火样品的巨磁阻抗效应和脆性进行对比.结果表明,经过应力脉冲电流处理后的样品,其阻抗变化率和灵敏度都显著高于无应力脉冲处理后的样品.淬态样品在9.34MPa拉应力下,经电流密度为930A/mm2的脉冲电流处理后,阻抗变化率可达到220%,灵敏度达到0.35%/A·m-1.用应力脉冲电流处理不仅可以显著提高巨磁阻抗效应,而且可以有效抑制样品长时间的等温退火带来的脆性问题.     

pH值对电沉积FeNi／Cu复合丝巨磁阻抗性能的影响

采用脉冲电沉积方法在φ90μm的Cu丝上制备出Fe20＋δNi80-8／Cu复合丝,并测试了巨磁阻抗（GMI）特性。实验表明：电镀液的pH值在1．48～3．1范围内变化,对于复合丝的镀层成分、厚度、表面质量及其巨磁阻抗（GMI）效应具有显著的影响。在pH为1．9～2．5时复合丝表面平整、缺陷少,在pH=2．03时获得了厚度为11μm、成分为Fe20．3Ni79．7的电镀沉积层。采用10mA的激发电流,频率f=29．6kHz时GMI效应达到631．5％,磁场的灵敏度在10kHz时达到560％／Oe,该频率远远低于CoFeSiB非晶丝材的频率。     

Fe—Cu—Cr—V—Si—B三明治膜的巨磁阻抗效应

用射频溅射法制备了Cu夹层的Fe-Cu-Cr-V-Si-B三明治膜,在不同条件下对样品进行了退火处理,在最佳退火条件下,样品软磁特性得到明显改善,从而获得了优良的巨磁阻抗（GMI）效应,研究了GMI效应与交变电流频率f和外加直流磁场H关系,在5MHz的特征频率下,最大的横向阻抗比△ZH/Zm达91%。由于样品的三明治结构,横向磁阻抗比明显优于纵向。     

NiFeSiMnMo/CU/NiFeSiMnMo多层膜的非线性巨磁阻抗效应

观察用蒸镀法制备的NiFeSiMnMo／Cu／NiFeSiMnMo多层膜的巨磁阻抗效应,经过退火后,得到性能优良的坡莫合金材料,研究了GMI效应与交变电流频率,和外加直流磁场H的关系,样品在3MHz的频率下能够获得一个14．9％的非线性巨磁阻抗效应。     

Electroplastic Tensile Behavior of 5A90 Al–Li Alloys

The electroplastic(EP) tensile properties of 5A90 Al–Li alloys compared with thermal tension were investigated.The microstructural variation at different conditions was observed by SEM and TEM.The current density significantly influences the elongation and the flow stress.With increasing current density,wider and deeper dimples on the fracture surfaces and less dislocation density and pile-ups in the EP tension samples were observed compared with roomtemperature and thermal tension,which indicates the plasticity improvement and flow stress reduction.The EP effect(EPE) mainly results from a comprehensive function of Joule heating and pure EPE.Among them,Joule heating effect is perhaps a dominant factor.     

直流偏置电流对钴基非晶带环形磁芯巨磁阻抗效应的影响

将近零磁致伸缩系数的Co66.3Fe3.7Si12B18非晶薄带卷成环形后,在200Gs横磁场作用下,用密度为25A/mm2的脉冲电流退火30s,在穿过环形薄带圆心的直流电流产生的圆周磁场作用下的巨磁阻抗效应.激励电流频率f＞100kHz时,阻抗随圆周磁场的变化呈现对称双峰曲线;最大阻抗变化率（GMI）max随频率的升高而增大,当频率f=2MHz,幅值Ip=10mA时,（GMI）max=57%.直流偏置电流改变了非晶带横向磁导率,造成阻抗变化的不对称.偏置电流较小时,阻抗变化曲线的一边峰值得到加强,另一边峰值减弱;偏置电流较大时,两峰值都被削弱.阻抗变化的不对称性与激励电流的频率和直流偏置电流大小有紧密联系.     

Grain refinement of commercial pure Al treated by Pulsed Magneto-Oscillation on the top surface of melt

Commercial pure Al can be refined by Pulsed Magneto-Oscillation(PMO) treatment applied via a plate induction coil above the top surface of the melt. The proportion of the equiaxed zone area increases with decreasing Height to Diameter(H/D) ratios from 3.5 to1.8 and further to 1.0. Meanwhile, it increases and then decreases with increasing peak current for the three kinds of ingots with H/D ratios of 3.5, 1.8 and 1.0, respectively. However, when the H/D ratio decreases to 0.44, the area proportion of equiaxed zone can reach the maximum value with a lower peak current. FEA software simulation indicates that smaller H/D ratio results in larger current density, electromagnetic force and convection on the top surface of the melt, favoring nucleation and subsequent grain formation. Through evaluating Joule heating effect by PMO, it was found that the proper amount of Joule heating benefits grain refinement. Excessive Joule heating can reduce the size of the equiaxed zone and change the growth morphology of the grains.     

Electromigration of Pb-free solder under a low level of current density

In this study, current stressing experiments were conducted to investigate electromigration of 99.3Sn0.7Cu solder with Au/Ni UBM in BGA packaging. Although the average current density in the solder bump was only 0.4 × 10⁴ A/cm², the maximum value of the current density was 1.42 × 10⁵ A/cm², which exceeded the threshold value for electromigration to occur. Furthermore, the current caused substantial Joule heating which significantly rose the local temperature of the interconnection. A novel method, forced convection heat-transfer, was introduced to dissipate the Joule heating and cool down the interconnection. Hence, electromigration was achieved under a low level of current density, because the effect of thermal diffusion of atoms was minimized. Ni and Cu migration from the cathode side to the anode side driven by electrons was observed on both the chip and substrate due to the special symmetrical structure. At the low temperature, a few small pieces of intermetallic compound (IMC) were found in the solder bumps, because Ni and Cu diffused into the Sn by a combination interstitial and boundary diffusion. When the temperature approached the melting point of the solder, many large IMC regions appeared along the boundaries in the solder. Here it is believed that Ni and Cu had a high rate of volume diffusion into Sn at the high temperature.     

Co71.8Fe4.9Nb0.8Si7.5B15玻璃包覆非晶丝巨磁阻抗效应研究

本文研究了直流焦耳处理对Co71.8Fe4.9Nb0.8Si7.5B15玻璃包覆非晶丝巨磁阻抗效应的影响.随着处理电流的增大,阻抗最大变化率随之增加,直到最佳处理条件为70mA,阻抗最大变化率为282%.处理电流值进一步提高,阻抗最大变化率下降.本文还研究了偏置电流对经过70mA直流焦耳处理的C021.8Fe4.9Nb0.8Si7.5B15玻璃包覆非晶丝巨磁阻抗效应的影响.随着偏置电流的增加,非对称性逐渐增强,直到偏置电流为2mA;当偏置电流继续增大时,非对称性逐渐减弱.     

Giant magnetoimpedance effect in Fe-Zr-Nb-Cu-B nanocrystalline ribbons

The giant magnetoimpedance effect of the nanocrystalline ribbon Fe84Zr2.08Nb1.92Cu1B11 (atom fraction in %) was investigated. There is an optimum annealing temperature (TA=998 K) for obtaining the largest GMI (giant magneto-impedance) effect in the ribbon Fe84Zr2.08Nb1.92Cu1B11. The ribbon with longer ribbon length has stronger GMI effect, which may be connected with the demagnetization effect of samples. The frequency fmax, where the maximum magnetoimpedance GMI(Z)max =[(Z(H)-Z(O)/Z(O)]max occurs, is near the intersecting frequency fi of the curves of GMI(R), GMI(X), and GMI(Z) versus frequency. The magnetoreactance GMI(X) decreases monotonically with increasing frequency, which may be due to the decrease of permeability. In contrast, with the AC (alternating current) frequency increasing, the magnetore-sistance GMI(R) increases at first, undergoes a peak, and under then drops. The increase of the magnetoresistance may result from the enhancement of the skin effect with frequency. The maximum magnetoimpedance value GMI(Z)max under H=7.2 kA/m is about -56.18% at f= 0.3 MHz for the nanocrystalline ribbon Fe84Zr2.08Nb1.92Cu1B11 with the annealing temperature TA=998K and the ribbon length L=6cm.     

直流电流作用下AZ91D镁合金半固态等温处理过程中的组织演变

考察了直流电流密度、等温温度及等温时间对AZ91D镁合金半固态组织的影响,对电流影响组织演变的机理进行了探讨．实验结果表明：当等温温度和等温时间一定时,随着电流密度的增加,初生相变得圆整,初生相的尺寸有所减小．但电流密度过高时,初生相尺寸有所增加．直流电流可以加速半固态等温处理的组织演化过程,明显改善枝晶球化效果．直流电流增加扩散激活能,增大溶质原子的扩散系数,促进溶质原子的扩散,从而加速半固态等温过程的组织演化;直流电流作用下的电迁移效应、Joule热效应和Peltier效应都将促进枝晶的熔断和球化．     

SOFT MAGNETIC PROPERTIES AND GIANT MAGNETOIMPEDANCE EFFECT IN MAGNETIC FIELD–DEPOSITED FeCuCrVSiB FILMS

采用射频溅射法, 在无磁场和施加72 kA/m的纵向磁场下制备了FeCuCrVSiB软磁合金薄膜样品, 对沉积态样品的软磁特性和巨磁阻抗(GMI)效应进行了测量和分析. 结果表明, 在制备过程中加磁场可明显改善材料的软磁性能, 与无磁场沉积态相比, 样品的矫顽力从1.080 kA/m降低到0.064 kA/m, 在13 MHz频率下有效磁导率比从10%增加到106%. GMI效应与磁导率比的大小密切相关. 无磁场沉积态样品没有检测到GMI效应, 而磁场沉积态样品则具有显著的GMI效应. 在13 MHz 的频率下, 最大纵向和横向巨磁阻抗比分别高达22%和20%. 这些结果都优于厚度几乎相同的退火态FeCuNbSiB薄膜的GMI特性.