Precipitation in Ni—35 at.pct Cr Alloy

Precipitation study was carried out in Ni-35 at,pct Cr alloy by measuring electrical resistivity at different ageing temperatures and long ageing times.During ageing,it was observed that electrical resistivity initially rose with ageing time and then fell after very long ageing at a constant temperature.The initial increase in resistivity during ageing may be attributed to the formation of GP zones/Cr-rich precuipitates at early stages by nucleation process and decrease in resistivity,and after attaining a maximum,is due to the growth of precipitate particles and subsequently by coarsening of these precipitates.The results of electrical resistivity measurements during ageing were confirmed by X-ray diffraction analysis indicating the formation of a Cr-rich phase and a Cr3Ni2 phase in the Ni matrix.     

残余应力对SrRuO3薄膜磁学及电输运性能的影响

采用射频磁控溅射法在单晶SrTiO₃ (STO)衬底和硅(Si)衬底上制备出不同取向的SrRuO₃ (SRO)薄膜, 对薄膜的残余应力进行了分析, 并研究了应力对不同取向SRO薄膜磁学性能与电输运特性的影响。根据X射线衍射(XRD)结果分析可知, Si基SRO薄膜为多晶单轴取向薄膜, 且应力来源主要为热失配拉应力; STO基SRO薄膜为外延薄膜, 其应力主要为热失配压应力和外延压应力; 磁学性能测试表明, (001)取向SRO薄膜比(110)取向薄膜拥有更高的居里温度T_C; 压应力提高了(001)取向SRO薄膜的T_C, 却降低了(110)取向薄膜的T_C。电阻性能测试表明, 对于在同种类型衬底上沉积的SRO薄膜, (001)取向的薄膜的剩余表面电阻比(RRR)高于(110)取向的薄膜。另外, 拉应力引起了薄膜微结构的无序度增加, 弱化了表面电阻率的温度依赖性, 提高了金属绝缘体转变温度(T_MI)。     

Peculiarities of the electrical resistivity and structural-magnetic transformations in Fe-18r-(10–25)Ni steels at low temperatures

The change of the electrical resistivity of austenitic FeCrNi steels containing 18 wt % Cr and 10 to 25 wt % Ni has been studied in the temperature range 4.2 to 293 K. Peculiarities of the electrical resistivity — the change in gradient of p(T) curves and the nonmonotonic p dependence (percent of nickel) of predeformed samples - are discussed considering the structural and magnetic transformations in steels. The assumption of a magnetic state at low temperatures in the steels studied is confirmed by the change of electrical resistivity in the steels in a constant magnetic field at 4.2 K.     

Thermophysical Properties of Undercooled Liquid Cu–Ni Alloys

Experimental data for the surface tension, density, and electrical resistivity of undercooled liquid Cu–Ni alloys of different compositions and at different temperatures are presented. The experiments were performed in facilities that combine the containerless positioning method of electromagnetic levitation with contactless measurement techniques. Although Cu–Ni alloys are rather simple from a chemical point of view, the data for density, surface tension, and electrical resistivity unveil the occurrence of short-range atomic order processes in the melt. For the density this manifests in a composition-dependent excess volume, for the surface tension in smaller values due to an increased surface segregation, and for the electrical resistivity in a deviation from the linear temperature dependence at low temperatures.     

Effect of processing conditions on microstructure and electrical characteristics of Ni thin films

Ni thin films with an intermediate layer of Cr were prepared by using dc magnetron sputtering under different conditions. Effects of deposition temperature, post-deposition annealing on the microstructure and the electrical characteristics were investigated. The relationship between film microstructure and its resistivity was analyzed. It was found that the crystal grains aggregated into large ones when the deposition temperature reached or exceeded 150 °C. This could be explained that high deposition temperature conduced high activation energy, which increased surface mobility of the adatoms. Annealing treatments resulted in the densification of the films. Resistivity of the films strongly depended on grain size and crystallinity. The influence of Cr intermediate layer on the resistivity was also discussed. Compared to annealing treatment, the deposition temperature exhibited larger controlling effect on film resistivity.     

Synthesis and Thermophysical Studies of Nanoferrites

Soft ferrites are very useful for a wide variety of technological applications especially in high frequency devices due to high resistivity and low eddy current losses. Co nanoferrite particles were synthesized by co-precipitation method and characterized to understand the microstructure and electrical transport properties. The composition was varied by changing the ??A?? concentration in Co_1?x A _x Fe₂O₄ (A= Zn, Ni) nanoparticles with stoichiometric proportion (x) varying from 0.0 to 1.0. X-ray diffraction was used for structural analysis. Then samples were sintered at 550?°C and 750?°C for 2 hours, characterized by X-ray diffraction at room temperature and DC electrical resistivity measurements were done as a function of temperature. The effects of sintering on structure were investigated. Activation energy was calculated from DC electrical resistivity data as a function of temperature.     

Structural and transport properties of SrRuO3 thin films grown by MOCVD on (0 0 1) SrTiO3 substrates: The role of built-in strain and extra phases

Pure SrRuO₃ (SRO) thin films and SRO thin films containing the extra metallic phases Ru, RuO₂ and Sr₃Ru₂O₇ were deposited by MOCVD on (0 0 1) SrTiO₃ substrates under different conditions (Ru/Sr and Ar/O₂ ratio in the gas phase, substrate temperature, supersaturation). The single-phase compressively-strained SRO film is of high structural quality and shows a ferromagnetic transition at a suppressed Curie temperature (T_c) of about 142 K and low electrical resistivity (230 μΩ cm). Under certain deposition conditions Ru and RuO₂ extra phases form leading to a reduced room temperature resistivity of 100 μΩ cm. On the other hand, the presence of Sr₃Ru₂O₇ increases the resistivity to 385 μΩ cm. We have observed that the existence of the extra phases caused a slight shift of T_c towards the bulk value, while relaxation of the lattice strain resulted in increase of T_c to 160 K. The deviation from the stoichiometric composition in films with extra phases is also confirmed by the residual electrical resistivity ratio. On the other hand, the pure SRO films, the compressively strained and the plastically relaxed exhibit a stoichiometric ratio.     

Composition Dependence and Irradation Effects on Residual Resistivity in Cu-Al Alloys

Residual electrical resistivity due to short-range order has been calculated for Cu100-xAlx (x=9.13,13.56, 14.5 and 14.76 in at pct) alloys using pseudopotential approach, and the results have been discussed in the light of experimental studies of the local-order structure of these alloys. In case of Cu85.5Al14.5, change in the total residual electrical resistivity due to neutron-irradiation effects has been estimated by including contributions from the short-range order and static atomic displacement correction. Our results show a decrease in the residual resistivity in the irradiated Cu-Al solid solution as compared to the unirradiated sample. This is in accordance with the experimental results     

Microstructure and In-plane Resistivity of Cu/Ni Multilayers

1.IDtroductiGnInrecellty6ars,interesthasgrowninmodulatedcompositestructurescomposedofperiodicallychang-inglayersoftwodifferentmaterials.Itwasshownthatthematerialsmayacquireimprovedqualitiestothoseofcorrespondingpuremetalswhenthemodu-lationwavelengthisverythinatafewnanometersinthickness.ItiswellknownthattheCu/Nimultilayershavebeenstudiedalotbecauseofitsabnormalphysicalproperties,includingelectricalresistivity[1,2],elasticmoduli[3],magneticproperties['l.Asthethicknessofanindividuallayerinmulti…     

Resistometric study on kinetics of reversible short-range ordering and crossover effect in Fe15Ni63Si8B14 metallic glass

The kinetics of reversible short-range ordering (SRO) and crossover effect in the fully stabilized Fe₁₅Ni₆₃Si₈B₁₄ metallic glass were examined by measurements of electrical resistivity change. The kinetic parameters for reversible SRO in the narrow temperature range from 240 to 280° C were determined to be 1.93eV for the activation energy, 8.6×10^–16sec for the preexponential factor and 2.3 for the width of the distribution of relaxation times on the assumption of a log-normal distribution. The crossover effect in reversible short-range ordering and disordering was clearly observed.     

Ni/PTCR陶瓷复合材料的显微结构与再氧化效果

用金属Ni复合的方法降低PTCR陶瓷的室温电阻率,采用草酸镍分解法制备了Ni/PTCR陶瓷复合材料,并对其显微结构进行了表征,研究了再氧化对PTCR效应的恢复和显微结构对再氧化效果的影响.结果表明,热处理可以明显地恢复复合材料的PTCR效应,而显微结构对热处理的效果有很大影响,在一定的工艺条件下这种Ni/PTCR陶瓷复合材料具有明显的PTCR特性和较低的室温电阻率.     

Electrical properties of thin metal zinc films

Thin metal zinc films 40 to 200 nm thick are deposited by thermal evaporation at room temperature onto glass substrates with a deposition rate of 0.2 to 0.7 nm sec^–1. The electrical resistivity is measured as a function of film thickness, deposition rate and annealing temperature. The experimental results show that electrical resistivity decreases as the film thickness, deposition rate and annealing temperature increase, while the temperature coefficient of resistivity increases with the increase in the film thickness. The calculated values of the activation energy for the conduction electrons increases as the film thickness and deposition rate increase. The well known Fuchs-Sondheimer model is applied for zinc films. The theoretically calculated values for the electrical resistivity and the temperature coefficient of resistivity are in good agreement with the experimental results.     

The effect of aluminum content on phase constitution and heat treatment behavior of Ti–Cr–Al alloys for healthcare application

As life expectancy steadily increases, developing reliable functional materials for healthcare applications gains importance. Titanium and its alloys, while attractive for such applications, are expensive. The present investigation suggests that it may be possible to reduce costs by using new, low-cost beta Ti alloys. To assess their reliability, the heat treatment behavior of beta Ti alloys, Ti–7 mass% Cr with varying Al content (0%, 1.5%, 3.0% and 4.5%), was investigated through electrical resistivity and Vickers hardness measurements. In the Ti–7Cr–0Al alloy quenched from 1173 K, only the beta phase was identified by X-ray diffraction (XRD). In Ti–7Cr–1.5 to 4.5 Al alloys, XRD detected both beta and orthorhombic martensite. On isochronal heat treatment behavior of Ti–7Cr–3.0, 4.5 Al alloys, resistivity at liquid nitrogen temperature and resistivity ratio increased between 423 and 523 K.These increases are due to reverse transformation of orthorhombic martensite to the metastable beta phase.     

Effect of cerium addition to Ni–Cr anode electrode for molten carbonate fuel cells: Surface fractal dimensions,wettability and cell performance

The geometrical and chemical effects of cerium (Ce) addition to Ni–Cr anode electrode in molten carbonate fuel cells (MCFCs) were investigated by measuring the fractal dimensions and wettability of four types of anode electrode with Ce added up to 5 wt.%. In addition, their cell performances were investigated through a single cell operation test and their results were explained based on the wettability of the anode electrodes. The addition of Ce to the anode electrode increased the fractal dimensions and wettabilities of the electrodes. Despite the even larger electrical resistivity of Ce compared to that of Ni and Cr, the electrical resistances of the Ce-added anode electrodes were slightly increased with increasing level of Ce addition. This might be ascribed to the greater wettability of the Ce-added anode electrode that enhanced the cell performance. Therefore, the greater wettability of the Ce-added anode electrode might compensate for its relatively larger electrical resistance. Considering these results, more stable cell operation with a longer potential lifespan was achieved with the Ce (3 wt.%)-added, Ni (90 wt.%)–Cr (7 wt.%) anode electrode, compared to those of the Ce-free Ni–Cr anode electrode.     

Coulomb blockade effects in silicon nanoparticles embedded in thin silicon-rich oxide films

Silicon nanoparticles (Si-nps) embedded in silicon oxide matrix were created using silicon-rich oxide (SRO) films deposited by low pressure chemical vapour deposition (LPCVD) followed by a thermal annealing at 1100?°C. The electrical properties were studied using metal-oxide-semiconductor (MOS) structures with the SRO films as the active layers. Capacitance versus voltage (C-V) exhibited downward and upward peaks in the accumulation region related to charge trapping and de-trapping effects of Si-nps, respectively. Current versus voltage (I-V) measurements showed fluctuations in the form of spike-like peaks and a clear staircase at room temperature. These effects have been related to the Coulomb blockade (CB) effect in the silicon nanoparticles embedded in SRO films. The observed quantum effects are due to 1?nm nanoparticles.     

Study of deformation and aging behaviors of a hot rolled–quenched Cu–Cr–Zr–Mg–Si alloy during thermomechanical treatments

The deformation and aging behaviors of a hot rolled–quenched Cu–Cr–Zr–Mg–Si alloy were investigated by microhardness and electrical resistivity measurements, and transmission electron microscopy observations. The resistivity of aged alloy increases almost linearly with increasing of the secondary cold deformation reductions, and a faster and larger increase in resistivity of the peak-aged alloy is found during the deformation process due to the occurrence of resolution phenomenon. Quantitative analysis shows that about 0.0385 wt.% solutes are re-dissolved into the peak-aged alloy after 70% cold deformation. Results of the following aging treatment show that the deterioration caused by resolution phenomenon in electrical properties can be eliminated by the secondary aging treatment. A good combination of high hardness and low resistivity can be achieved in the Cu–Cr–Zr–Mg–Si alloy after suitable thermomechanical treatments.     

Cr-Si-Ni-N电阻薄膜的晶化与氧化特性

在PN2／PAr2分压比分别为0％，2．5％，5％，10％的溅射气氧化中制备了不同氮含量的Cr-Si-Ni-N薄膜，并研究了薄膜在热处理过程中的晶化，氧化行为以及电性能变化。结果表明，非晶Cr-Si-Ni-N薄膜在加热过程中，将析出晶化相CrSi2，随薄膜中氮含量增加，晶化相的形核与长大减缓，然而，薄膜的抗氧化能力得到提高。与低氮含量Cr-Si-Ni-N薄膜相比，高氮含量Cr-Si-Ni-N薄膜的电阻值在热处理过程中变化较小，欲获得较小电阻温度系数（TCR）需要更高的退火温度。     

Mo元素对ZG04Cr13Ni4Mo不锈钢力学性能的影响

对12%Cr和13%Cr系列ZG04Cr13Ni4Mo不锈钢进行893 K一次回火和893 K+863 K二次回火处理,使用热膨胀仪、X射线衍射仪和室温单轴拉伸等手段研究了Mo含量对这两个系列不锈钢的相组成和力学性能的影响。结果表明,随着Mo和Cr含量的提高钢的奥氏体化开始点(A_s)温度逐渐降低。不同Mo含量的钢经过893 K两相区温区一次回火处理,在加热和保温过程中马氏体向逆变奥氏体的转变量,与回火冷却至室温得到的逆变奥氏体含量不同。这种不同,导致12%Cr系列ZG04Cr13Ni4Mo钢随着Mo含量从～0.3%提高到～0.6%其屈服强度略有降低而抗拉强度略有提高,而Cr含量提高到13%Cr随着Mo含量的提高ZG04Cr13Ni4Mo钢经893 K回火后其屈服强度和抗拉强度都小幅度提高。     

碳纤维-Ni/尼龙66复合材料的制备与性能表征

为制备低电阻率的尼龙66基复合材料,以碳纤维和镍粉(Ni)填充尼龙66制备碳纤维-Ni/尼龙66高导电复合材料。研究填料表面改性和含量对碳纤维-Ni/尼龙66复合材料导电性能和力学性能的影响。结果表明:KH550改性碳纤维和Ni有助于降低碳纤维-Ni/尼龙66复合材料的电阻率。碳纤维-Ni/尼龙66复合材料的电阻率随着碳纤维和Ni含量的增加而减小,且碳纤维和Ni填充尼龙66的导电逾渗阈值均为20wt%,此时制备的碳纤维-Ni/尼龙66复合材料的电阻率为455Ω·cm,熔融温度为202.2℃。碳纤维-Ni/尼龙66复合材料的弯曲强度和拉伸强度随着碳纤维或Ni含量的增加而先增大后减小。当Ni含量为20wt%时,碳纤维-Ni/尼龙66复合材料的弯曲强度和拉伸强度在碳纤维含量分别为20wt%和10wt%时达到最大值,分别为98MPa和70 MPa;当碳纤维含量为20wt%时,碳纤维-Ni/尼龙66复合材料的弯曲强度和拉伸强度则在Ni含量为30wt%和20wt%时达到最大值,分别为120 MPa和67 MPa。     

The influence of processing temperature on the structure and properties of mesophase-based polygranular graphites

Two polygranular graphites were prepared by sintering a coal-tar pitch based mesophase and a naphthalene-based mesophase. The influence of temperature on the structural (density, porosity and light texture), mechanical (flexural strength) and electrical (electrical resistivity) properties of the carbons was studied at different stages of carbonization/graphitization (400–2600°C). The results show that the density of the materials increases continuously with temperature, pores mainly appearing below 800°C, during the low-sintering phase and at the initial stages of the solid-sintering process. Above this temperature, porosity decreases due to the densification of the materials. Densification is clearly evidenced by a reduction in interlayer spacing and an increase in crystallite size. Flexural strength and electrical resistivity follow a different trend depending on the temperature range. Thus, flexural strength reaches its maximum value at 1000°C, while electrical resistivity decreases continuously with temperature. Any variation in these properties is mainly related with porosity and crystallographic order. The different composition of the raw materials causes structural, mechanical and electrical changes to occur to different extent in both materials.