离子取代镍基铁氧体的性能及吸波涂层优化设计

在同等实验条件下,以镍铁氧体为基体,通过溶胶-凝胶法,制备二元镍基复合铁氧体Ni0.5A0.5Fe2O4(A=Zn,Co,Mn,Cu)。用X射线衍射仪、扫描电子显微镜、振动样品磁强计和矢量网络分析仪对粉末的结构及电磁性能进行表征并对其吸波性能进行优化设计。结果表明:4种离子取代后均能形成在室温条件下具有超顺磁性的纯净镍基铁氧体粉末。离子取代使铁氧体样品的复介电常数实部ε′增大,虚部ε″在2~6 GHz和13~18 GHz变小,在6~13 GHz增大。Zn2+、Mn2+、Cu2+3种离子取代样品与未进行离子取代的NiFe2O4相比,其复磁导率实部μ′变化不大,而Co2+离子取代样品的μ′整体要大于其他几种离子取代样品及未取代样品的μ′;在2~11 GHz进行Zn2+、Co2+、Mn2+3种离子取代样品的虚部μ″变大,且以Ni0.5Zn0.5Fe2O4的最大,Cu2+取代样品的虚部μ″与未取代样品的虚部μ″相比变化不大。利用传输线理论优化设计时发现,Co2+取代后的复合铁氧体没有匹配点,Zn2+取代后的复合铁氧体匹配效果最好,在最佳匹配厚度为5.63 mm时,其最小反射率峰值为-36.26 dB,小于-10 dB的频宽可达4.7 GHz。     

Sr0.8Re0.2Fe11.8Co0.2O19(Re=La,Nd)的制备、表征及吸波性能

采用溶胶凝胶法,制备Sr0.8Re0.2Fe11.8Co0.2O19(Re=La,Nd)复合铁氧体。采用X射线衍射仪、扫描电子显微镜、振动样品磁强计和矢量网络分析仪表征粉体的结构及电磁性能。结果表明:得到的粉体为纯净的磁铅石型铁氧体,La3+掺杂样品的各项性能明显改善。在室温条件下,稀土离子掺杂后样品的Ms受到稀土离子掺杂的影响较小,Hc则明显提高;La^3+掺杂样品和Nd3+掺杂样品的Ms值接近,前者的Hc值则明显强于后者的,Sr0.8La0.2Fe11.8Co0.2O19的Ms和Hc分别为58.08A m^2/kg和362.0kA/m。稀土离子掺杂使铁氧体样品的复介电常数(ε′和ε″)增大,与Nd3+掺杂样品相比,La3+掺杂样品的介电损耗和磁损耗改善更为明显。利用传输线理论优化设计时发现,在1.2~2.4 mm之间,随着厚度的增加,Sr0.8La0.2Fe11.8Co0.2O19的反射率峰值先减少后增加,逐渐向低频移动;在厚度为2.0 mm时,其反射率峰值达到最小值为27.8 dB(11.8 GHz),小于10 dB的吸波带宽为5.2 GHz(9.5~14.7 GHz)。     

钡铁氧体/Fe-Ni合金复合材料吸波性能研究

采用溶胶-凝胶法制备Z型钡铁氧体Ba3Co2Fe24O41,真空球磨法制备Fe Ni3合金,通过真空球磨将Fe Ni3合金添加到铁氧体中,并对该复合进行退火处理。对样品电磁参数测定发现,Fe Ni3合金的添加有利于减小样品的复介电常数虚部ε',提高复磁导率虚部μ',而且退火处理可进一步提高μ'。吸波性能测试发现,Fe Ni3的添加使样品对微波的吸收量有明显提升,尤其在低频率段吸收量有近3倍的提高,而退火后样品的微波吸收量又有所提高,且整体波动幅度也有所减小。     

Cu2+掺杂调控NiZn铁氧体的P波段吸波性能

目的 研究离子掺杂对NiZn铁氧体电磁特性的影响,提高NiZn铁氧体的P波段吸波性能。方法 以NiO、ZnO、Fe2O3、CuO等为原料,采用高温固相反应法,通过球磨、预烧、造粒以及烧结等工艺,制备Cu²⁺掺杂的Ni0.22Zn0.66CuxMn0.04Co0.08–xFe2O4(x=0.04、0.05、0.06、0.07)铁氧体样品。通过XRD、VSM和SEM分别表征样品的晶格特征、磁学特性和微观形貌,利用阻抗分析仪对样品的电磁特性进行测量。结果 Cu²⁺掺杂量的增加引起NiZn铁氧体的A-B超交换作用减弱和磁晶各向异性降低,样品的Ms、Hc和Mr都呈现出减小的趋势。样品的复磁导率与其磁特性关系密切,随着Cu²⁺的增加,实部μ?减小,而虚部μ?增大。此外,Cu²⁺掺杂量的增加对Fe²⁺与Fe³⁺之间的电子迁移率产生影响,使得复介电常数实部ε?增大,而ε?增大的主要原因是Cu²⁺掺杂量的增加导致铁氧体内部产生了晶格缺陷。Cu²⁺的掺杂量对样品的P波段吸波性能影响显著,随着Cu²⁺掺杂量的增加,NiZn铁氧体的阻抗匹配特性明显改善,电磁衰减能力显著提高,这进一步降低了样品的最佳吸波匹配厚度。掺杂量x=0.07的NiZn铁氧体样品,在厚度为6.6 mm时,实现了有效吸波带宽完全覆盖P波段。结论 通过调节Cu²⁺的掺杂量可以调控NiZn铁氧体的P波段吸波性能,增加Cu²⁺掺杂量对于降低样品的P波段吸波匹配厚度有积极作用。     

钙钛矿型锰氧化物La0.8Sr0.2MnO3的高频性能

采用溶胶-凝胶法制得La0.8Sr0.2MnO3氧化物多晶样品。通过XRD、SEM对样品的微观结构进行了分析,结果表明:所得样品为钙钛矿结构,样品的颗粒大小比较均匀,平均粒度约100nm。利用阻抗分析仪对样品的介电常数和磁导率的频谱(10MHz～1GHz和1MHz～1GHz)进行了研究。研究表明,在整个测试频率范围内,La0.8Sr0.2MnO3的介电常数实部和虚部随频率的升高而降低。La0.8Sr0.2MnO3的复磁导率的频谱谱线为典型的弛豫型谱线,磁导率实部在1MHz时为6.2,共振频率fr为50MHz,共振时虚部峰值为2.8;磁谱测试表明材料的弛豫损耗峰出现在频率f≤300MHz的频率范围内,在此频率区域引起损耗的机制主要是畴壁共振。     

燃烧合成法制备N掺杂SiC粉体及其微波介电性能

采用燃烧合成法,以硅粉和炭黑为原料、固态氮化剂α-Si3N4为掺杂剂及聚四氟乙烯(polytetrafluoroethylene,PTFE)为化学活性剂,制备N掺杂的β-SiC粉体吸收剂。通过X射线衍射分析和扫描电子显微镜对燃烧产物进行了表征。结果表明:PTFE含量为10wt%时,燃烧产物中β-SiC的纯度较高,具有较好的颗粒形貌。利用矢量网络分析仪测试了样品在8.2～12.4GHz频率范围的微波介电常数,10wt%PTFE样品显示了最大的介电常数实部ε′、虚部ε″和损耗角正切tanδ。     

多层吸波材料反射损失计算机模拟

设定了六种不同的吸波材料,它们具有不同的相对磁导率的实部（μ＇r）与虚部（μ＇＇r）以及不同的相对介电常数的实部（ε＇r）与虚部（ε＇＇r）.按照Kraus的传输线阻抗转换方程,迭代计算了厚度3mm,1～6层吸波涂层的反射损失在2～18GHz频率范围随频率的变化.计算结果表明,涂层排列方式对反射损失随频率的变化规律有很大影响.     

低稀土含量的纳米复相α-Fe/Nd2Fe14B淬态合金微结构与微波电磁特性研究

对低稀土含量的Nd6Fe91B3合金进行熔体快淬处理,制备了由α-Fe相和少量的Nd2Fe14B相组成的纳米复相材料,并对其进行球磨处理25h。研究了快淬速度对淬态合金的相组成、微观结构、微波电磁性能的影响规律。研究结果表明,随着淬度的提高,淬态合金中高磁晶各向异性的Nd2Fe14B相逐渐减少,材料的自然共振频率向低频移动,但样品微波磁导率随淬速的提高而升高。淬速为40m/s的样品微波磁导率虚部在4.17GHz获得最大值μ"rmax=4.66,其实部在1.55GHz获得最大值μ’max=7.88。同时,低稀土含量的纳米复相α-Fe/Nd2Fe14B材料具有良好的微波电特性,其复介电常数在2GHz附近出现共振。由于磁损耗和电损耗共同作用,有利于该材料在GHz频段电磁波吸收材料中的应用。     

Nd2Fe14B／α-Fe复相材料微结构对微波复磁导率的影响

采用熔体快淬、晶化退火工艺及机械球磨方法制备了Nd2Fe14B／α-Fe纳米晶双相材料。研究了机械球磨工艺对材料的微结构、形貌和微波复磁导率的影响。结果表明：适当的机械球磨工艺可使材料粒度变细、变薄，晶粒细化，增强软、硬磁相晶粒间的交换耦合作用，提高其磁各向异性和饱和磁化强度，从而调节材料的共振吸收峰频率和微波复磁导率。球磨25h样品的复磁导率虚部μ’在3GHz达2．6，μ”在12GHz达1．2，μ”在30．5GHz达0．85，Nd2Fe14B／α-Fe纳米晶双相材料共振峰可控，不仅可应用于厘米波而且可应用于毫米波吸收材料的设计中。     

X波段宽频大损耗BaZnCo-Z型铁氧体的磁性和微波吸收特性

采用柠檬酸溶胶.凝胶自蔓延法制备了Ba3(Zn1-xCox) 2Fe24O41(x=0.2,0.4,0.6,0.8)铁氧体纳米晶颗粒.材料相结构、静态磁参数和电磁参数分别通过XRD、VSM和矢量网络分析仪测得.结果表明,随着Co含量的增加,样品静态磁性能的改变与Co2+在点阵中的占位密切相关;样品的复磁导率实部的变化较好的符合单畴畴转磁化理论,而其虚部变化还要受到旋磁阻尼系数的影响;样品的复介电常数受到Co含量和晶粒尺寸的共同影响.反射功率损耗测试表明,在X波段1 mm厚x=0.6样品的反射功率损耗最大吸收值可达49.907 dB,并且反射功率损耗大于30 dB和20 dB的频宽分别为3.56 GHz和4.26 GHz.可见x=0.6样品在整个X波段内具有非常好的微波吸收性能,是X波段理想的微波吸收剂.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。