【作者】 黄晓莉；

【导师】 武高辉；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2009， 博士

【摘要】 本文采用电沉积方法制备了泡沫Fe-Ni材料,并利用光学显微镜(OM),扫描电子显微镜(SEM)、透射电镜(TEM)、物理性能测量系统(PPMS)、同轴测试装置、点聚焦透镜天线、电子拉伸机等多种手段对其微观组织、力学性能、电磁屏蔽性能进行了系统的研究,并探讨了多孔材料的微观结构与性能的相关性。论文综合考虑了金属网状材料以及坡莫合金在电磁屏蔽应用中的优缺点,提出以磁性材料Fe-Ni系合金为骨架,以透气性的三维网状材料为结构,制备具有软磁特性的泡沫Fe-Ni材料,并研究其在恒磁场以及交变电磁场屏蔽中的电磁屏蔽效能。泡沫Fe-Ni材料的密度为0.2g/cm~3～1.2g/cm~3,致密度为2.3%～12%。在空间中近似认为由正十四面体紧密堆积而成,泡沫Fe-Ni材料的骨架中空,骨架壁厚由两端到中间逐渐减薄,骨架截面积近似于圆形。热处理后,泡沫Fe-Ni与传统的1J50坡莫合金的主要成分相同,但其杂质含量较1J50多。骨架上Fe、Ni两种元素没有完全扩散之前,骨架上元素的分布为连续的梯度分布状态,主要的结构为与1J50相同的γ-(Fe,Ni)相。利用积分叠加方法建立了泡沫Fe-Ni磁导率与元素扩散的相关性。热处理工艺不同对材料宏观磁导率的影响主要来源于泡沫骨架上Fe、Ni两种元素分布的不同,且遵从的关系。结果表明,当Fe、Ni元素呈现一定的梯度分布时,材料的磁导率出现极大值。而不同孔径材料达到最佳磁性能的保温时间因为泡沫骨架半径的不同而不同。90ppi,厚度为3mm,致密度为12%的泡沫Fe-Ni热处理后,骨架表面γ-(Fe,Ni)的晶粒大小约在5μm ~ 30μm范围内,晶粒内部的磁畴多以条带状分布,不同晶粒之间的磁畴取向呈现一定的角度。材料的磁导率在外磁场强度为H=6Oe时达到最大,在静磁场和工频磁场下的屏蔽效能分别为8dB和21dB。使用Maxwell 2D软件模拟了多孔泡沫材料的磁场屏蔽效能与泡沫材料宏观结构参数之间的关系。结果表明,泡沫材料的磁屏蔽效能随着致密度的增加而增大,且当泡沫材料的致密度达到75%时,其磁场屏蔽效能与对应致密材料相差无几。选择适当的泡沫材料与致密材料组成双层方形屏蔽体时,其屏蔽效能与相应的致密材料相当,此时屏蔽体重量降低21.5%;若增大双层屏蔽体之间的空隙到8mm,磁场屏蔽效能增加24%,与圆形致密材料相差无几。利用积分叠加方法计算了热处理后Fe、Ni元素分布对泡沫Fe-Ni电导率的影响规律,结果表明:材料的电导率随着热处理温度的升高和保温时间的延长逐渐降低,导致泡沫Fe-Ni在30kHz ~1.5GHz范围内的屏蔽效能有2dB~4dB的降低。采用目前常用的几种理论模型分析了泡沫Fe-Ni材料的电导率随致密度的变化关系,结果表明,泡沫Fe-Ni的导电性能也随着材料致密度的增加而增加。电磁屏蔽效能测试表明,在30kHz~1.5GHz范围内,泡沫Fe-Ni的电磁屏蔽效能均大于60dB,且随着频率的增加逐渐降低;在2.6GHz~40GHz范围内,多孔Fe-Ni合金的电磁屏蔽随着频率的增加逐渐升高,且当f >26.5GHz时,其平均电磁屏蔽效能高于90dB。在频率200<f<400MHz,2GHz<f<15GHz范围内,泡沫Fe-Ni的电磁屏蔽效能与铝合金板相当,但其密度仅为铝合金板的1/3~1/2。与传统的不锈钢、铁网以及铜网相比,三维网状结构的泡沫Fe-Ni合金在宽频带内的屏蔽效能要远高于传统的二维网状结构。在整个测试的交变电磁场频率范围内,泡沫Fe-Ni的屏蔽机制为反射损耗和多次反射损耗共同作用的结果,增加材料的导电性以及多次反射界面都会提高泡沫Fe-Ni的电磁屏蔽效能。泡沫Fe-Ni的压缩曲线呈现比较典型的弹塑性形变行为,试样的变形主要分为三个阶段:弹性变形段,屈服平台阶段以及致密化阶段。应用Gibson经验公式并根据本试验材料的结构参数进行调整,得到泡沫Fe-Ni的表观屈服强度随着泡沫骨架长径比的增加而增加。更多还原

【Abstract】 In this paper, we designed open-cell iron-nickel foam, and systematically investigated the microsructure, mechanical properties, electromagnetic shielding effectiveness of the material by using optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), physical properties measurement system (PPMS), coaxial cable method and Focusing lens antenna, and discussed the relations between properties and microstructure.In the thesis, the adventige and disadventiges of metal mesh and permalloy in electromagnetic shielding are summarized and the factors influencing shielding effectiveness are analyzed. Accordingly, open-cell Fe-Ni foam with magnetic material Fe-Ni alloy frame in application in magnetic field and electromagnetic shielding are proposed.The density of open-cell Fe-Ni foam is in the range 0.2g/cm~3～1.2g/cm~3 and the relative density is 2.3%～12%. The open-cell foam is considered stacking by tetrakaidecahedron cell in the space and SEM observations indicate that the metal mass is clustered more toward the nodes along ligaments, and the cross-section of ligament is approximate as circle.Based on the analysis of X-ray fluorescence spectrometry and X-ray diffraction, a similar chemical composition and structure ofγ-(Fe, Ni) is found in open-cell Fe-Ni foam to solid permalloy 1J50 after heat treatment. Moreovere, the Fe and Ni is gradient distributied in the diffusion layer before they are uniform on a ligament.The relations between distribution of elements and magnetic permeability and electrical conductivity are established by integral method. It indicates the maximum magnetic permability is observed for a certain distribution of Fe and Ni before they are uniform distributed in the layer. The analysis of energy diffraction spectrometry indicates that holding time of heat treatment is different with different ligament to reach the maxium magnetic permability.As for the open-cell Fe-Ni foam of 90 ppi (poles per inch) with 3mm in depth and 12% relative density, the shielding effecitivness (SE) is 8dB and 26.5dB in magnetic field and magnetic field of 50Hz, respectively when it is heat treated for 3 hours at 1100℃. Moreover, the grain size ofγ-(Fe, Ni) increases with the holding time of heat treatment, and generally in the range 5μm ~ 30μm. The Magnetic Force Microscopy (MFM) shows that the magnetic domain is banded distribution in grain and there is certain orientation of magnetic domain between different grains.The SE value of open-cell Fe-Ni foam is simulated by Ansoft Maxwell 2D. In this method, the SE value is confirmed to increase with increasing relative density. And the SE is similar to that of solid permalloy when the relative density is 75%. All the results also show that the weight reduce 21.5 percentages when the solid shield with 3mm in depth is substitued by a two-layers shield of solid permalloy with 2mm in depth and foam with 3mm in depth of 81% porosity. Moreover, there is 24 percentages increase in SE value when the distance of two layer is 8mm.Furthermore, the electrical conductivity of open-cell Fe-Ni foams is also calculated by integral method. It shows the electrical conductivity decreses with the increase of temperature and the holding time and hence lead to 2dB ~ 4dB decrease in SE value in frequency range 30kHz~ 1.5GHz. The electrical conductivity also increases with the increasing relative density.The measurement of electromagnetic shielding effectiveness (EMSE) show that the SE value of open-cell Fe-Ni foam is more than 60 dB in the frequency range 30kHz~1.5GHz, and more than 90 dB when the frequency surpasses 26.5GHz. This SE value is similar to that of aluminum in the frequency range 200MHz~400MHz and 2GHz~15GHz, while a little 5dB lower than that of Al in 400MHz~1.5GHz.Compared to traditional materials like copper, iron and steel mesh, it shows better electromagnetic shielding application in wide frenquency band. Study on the mechanism of EMSE indicates he electromagnetic shielding of open-cell Fe-Ni foam is the common effect of reflection and multiple reflections in the whole frequency range investigated, and the SE value can be enhanced by the way either for the increase of electrical conductivity or the surfaces and interfaces of multiple reflections.Compressive stress-strain curve of open-cell Fe-Ni foam include three regions: elastic region, plateau region and densification region. The yield strenghth of open-cell Fe-Ni foam increase with the increasing aspect ratio of ligament更多还原