退火温度对微合金铁粉压缩性的影响

通过还原-磨选法制取的特种天然微合金铁粉具有优异的性能。为了提高铁粉的压缩性,研究了不同退火温度对微合金铁粉压缩性的影响。采用扫描电镜、X射线衍射和硬度测试,探讨了晶粒大小、显微硬度对微合金铁粉压缩性的影响。结果表明:不同温度退火后粉末形貌、松装密度和流动性变化不大;但退火温度对微合金铁粉的晶粒尺寸、显微硬度影响较大,进而影响压缩性。随着退火温度的升高,粉末的晶粒尺寸增大,显微硬度降低。粉末的压缩性随着晶粒尺寸的增加有所提升;同等压力下压缩性随着显微硬度的降低而提高。压力为500MPa时,显微硬度对粉末压缩性的影响最大。     

热成型工艺对镍包铁粉填充橡胶电磁屏蔽及隔声性能的影响

研究了热成型工艺对镍包铁粉填充橡胶电磁屏蔽性能及隔声性能的影响。结果表明:硫化时间随硫化温度的升高而降低,硫化时间过长及硫化温度过高对材料的电导率及电磁屏蔽性能均有不利影响。当硫化温度为150℃时,材料的电磁屏蔽性能最佳。硫化压力提高,材料的密度会得到提升,材料的隔声量相应得到提高。当硫化压力为40 MPa时,材料隔声量最高,达到34.9 d B。     

制备工艺对铁硅铝磁粉芯品质因数的影响

采用球磨制粉和模压成型法制备了FeSiAl磁粉芯,研究了绝缘剂用量、成型压力、退火温度和磁粉粒度对铁硅铝磁粉芯品质因数的影响.结果表明,随绝缘剂用量和成型压力的增大,磁粉芯的品质因数增大;退火温度升高,有助于降低磁粉芯的内应力,提高品质因数,但过高的退火温度会降低磁粉芯的品质因数;随着磁粉粒度的减小,磁粉芯品质因数增大.     

终轧温度对含钛铌超低碳铁素体不锈钢显微组织、织构和力学性能的影响

实验室研究了终轧温度对钛、铌复合添加的16%Cr超低碳氮铁素体不锈钢的显微组织、织构和力学性能的影响。结果表明,当终轧温度从940℃降低到800℃时,热轧退火钢板和冷轧退火钢板的铁素体晶粒尺寸均减小,因此采用低温终轧有利于细化铁素体晶粒。降低终轧温度,热轧退火后钢板中形成的γ纤维明显增强且比较均匀。由于织构具有遗传性,在冷轧退火钢板中也形成了均匀的γ再结晶织构。采用较低的终轧温度既有利于提高成型性又有利于改善材料的各向异性。     

冷轧Cu-15Cr原位复合材料组织和性能研究

经冷轧变形和中间退火制备了Cu-15Cr形变原位纤维增强复合薄板材料。用SEM、拉伸试验机和电阻率测试仪研究了变形量及退火温度对Cr纤维形貌、合金强度及导电性能的影响。结果表明:随合金变形量的增加,Cr纤维逐渐变薄、变宽,纤维间距逐渐减小,材料的抗拉强度和导电率都逐渐增大。退火温度升高,材料抗拉强度随之降低,导电率先升高后降低,退火温度为550℃时,导电率峰值为84.4%IACS;退火温度升高,Cr纤维依次发生球化,球化加剧、纤维断裂。最终变形量时,材料达到较好的综合性能匹配,退火前抗拉强度和导电率为694 MPa和78%IACS;500℃退火后抗拉强度和导电率为570 MPa和83%IACS。     

Fe-Ni-Cu-C合金粗粉注射成型工艺参数的优化

采用正交试验法研究了注射压力、注射温度、注射速度及其交互作用对注射成型坯质量的影响,评价了各参数对生坯质量影响的显著程度,优化了注射成型参数.试验结果表明,注射压力、注射温度、注射速度及注射压力与注射温度的交互作用对生坯抗弯强度影响显著,注射压力、注射温度及注射温度与注射速度的交互作用对生坯密度影响显著.注射压力增加,生坯密度和抗弯强度都增大;注射温度提高,生坯密度降低,注射温度在155～160 ℃之间时,生坯抗弯强度变化不大,超过160 ℃时抗弯强度明显降低.注射速度为60%时,生坯密度达到最大值.最佳注射成型工艺参数为:注射压力8 MPa,注射温度155 ℃,注射速度60%.     

低温烧结Ni0.2Cu0.2Zn0.6Fe2O4铁氧体的工艺条件研究

采用化学共沉淀法制备了Ni0.2Cu0.2Zn0.6Fe2O4铁氧体,研究了制备工艺及助烧剂对材料显微结构和电磁性能的影响.结果表明,成型压力、保压时间、烧结温度和助烧剂对NiCuZn铁氧体材料的生坯密度和饱和磁化强度等有显著影响.随成型压力的增加,当保压一定时间、添加一定量助烧剂时,生坯密度随之增加,饱和磁化强度也相应提高.并确定了能实现低温烧结且具有良好饱和磁化强度的工艺条件:压制压力300 Mpa,保压时间 4min,烧结温度900℃.     

铁硅铝磁粉芯磁导率的研究

采用粉末冶金法制备铁硅铝磁粉芯,研究了绝缘粘结剂用量、成型压力、退火温度和磁粉粒度对铁硅铝磁粉芯磁导率的影响.结果表明,随着绝缘粘结剂用量的增多,磁粉芯的磁导率减小;去应力退火有助于提高磁粉芯的磁导率,随退火温度的升高,磁粉芯的磁导率增大;随着磁粉粒度及成型压力的增大,磁粉芯的磁导率增大.     

高频陶瓷粉体/Fe磁粉芯的微观结构与磁性能研究

对高纯铁粉进行表面改性处理,处理后的铁粉分别与SiO2、Al2O3及TiO2粉体用高能球磨法进行复合,在模具中压制成型,然后进行热处理.结果表明:Al2O3/Fe复合粉体具有最佳的成型性能,经过模压后磁粉芯的致密度达到理论密度的75.4％.该磁粉芯经1000℃×1h热处理后,磁粉芯内铁粉出现冶金结合,当Al2O3陶瓷粉体含量大于3％时,生成典型的Al2O3/Fe复合材料,该复合材料的电阻大大高于铁基体材料,使得该磁粉芯的高频性能得到提高;当复合3％Al2O3陶瓷粉体时,Al2O3/Fe磁粉芯磁导率μi为44.58,中心频率f达到12.02 MHz,中心频率品质因素Q达到14.6,综合高频软磁性能最佳.     

Fe-硅酮树脂软磁复合材料的成形工艺与磁性能研究

采用具有良好耐高温性能的硅酮树脂作为绝缘包覆剂制备铁基软磁复合材料,并研究了硅酮树脂绝缘包覆和成型压力对软磁复合材料磁性能的影响。结果表明:在铁粉颗粒表面存在一层均匀的包覆层,包覆后的样品具有在高的电阻率和宽的频率范围内良好的频率特性。600 MPa压力下成型的3wt%硅酮树脂包覆样品具有低的磁损耗,在50 kHz时其磁损耗仅为未包覆样品的29.8%。样品的压制密度和磁导率实部值随成型压力的增大逐渐提高,但高的压力会破坏绝缘层的连续性,导致涡流损耗增加。     

Die wall lubricated warm compacting and sintering behaviors of pre-mixed Fe–Ni–Cu–Mo–C powders

Polytetrafluoroethylene (PTFE) emulsion was used as die wall lubricant. Die wall lubricating warm compacting and sintering behaviors of pre-mixed Fe–2Ni–2Cu–1Mo–1C powders were studied. Results show that green density and spring back effect of pre-mixed powders all gradually increased as the compacting pressure rose. The green density of pre-mixed powder increased with the rise of compacting temperature and then slightly fell, the maximal green density was obtained at 120–140 °C. The degree of effect of warm compaction conditions on green density in turn from big to small followed as compacting pressure, lubrication, compacting temperature, mixing method and compacting speed. Die wall lubrication in combination with warm compaction effectively increased the compact density of pre-mixed powder. Sintered density of pre-mixed Fe–2Ni–2Cu–1Mo–1C material first increased and then fell as the temperatures went up after compacts were sintered at different temperatures for 50 min, but the trends of sintering dilatation were quite the reverse. Sintered density first reduced and then increased with the going on of sintering time at 1300 °C, but the trends of dimension change after sintering were just the reverse.     

Electroless coating of Permalloy powder and DC-resistivity of alloy composites

A high-resistivity coating of Permalloy (Ni–17.81Fe–1.97Mo wt.%) powders for soft magnetic composites, SMC, was developed and characterized. The coating was made using the electroless plating method employing an aqueous solution of sodium and nickel phosphates. The chemical process led to the formation of a layer up to 1 μm thick deposited on each particle surface and composed of a mixture of Ni(OH)₂, P₂O₅ and NaPO₃ compounds, as shown by X-ray photoelectron spectrometry and X-ray powder diffraction studies. The effect of coating on electrical DC resistivity was evaluated on SMC obtained mixing the metal, coated or uncoated, and thermoplastic polymer PEEK (polyetheretherketone) powders, pressing the mixture at 800 MPa and heating in air up to melting the polymer (380–410 °C). The SMC made with coated powders showed an increase in resistivity of more than two orders of magnitude compared to that obtained with uncoated powders when the polymer ranged between 0.5 and 1.5 wt.%. This difference prevails in comparison with sintered materials processed at the same pressure and sintering in hydrogen at 1350 °C. Thus, this process would restrict the eddy currents which affect the performance of soft magnetic products for AC applications.     

Fe-VC-Fe<Subscript>3</Subscript>C nanocomposites produced by mechanical synthesis from various starting components

Methods of X-ray diffraction, Mössbauer spectroscopy, and electron and atomic force microscopy have been used to study the sequence of structural and phase transformations upon mechanical alloying, annealing, and compacting of iron-vanadium-carbon alloys produced from mixtures of various compositions, such as powders of Fe (70 at %) and VC (30 at %); powders of pure elements of Fe (70 at %), V (15 at %), and graphite (15 at %); powders of Fe (70 at %) and V (15 at %) and toluene. It has been shown that in all cases the mechanical alloying results in the formation of nanocomposite powders with a complex phase composition representing a mixture of an α-Fe-based solid solution, carbide-based X-ray amorphous phase, and vanadium carbide VC. The annealing and compacting lead to the formation of an Fe-VC-Fe₃C nanocomposite. The use of liquid organic media as the source of carbon makes it possible to obtain materials with a narrow grain-size distribution and a uniform spatial distribution of carbide phases, which results in high values of microhardness, to 12 GPa.     

Recrystallization of the ultradispersed structure of pure iron formed at different stages of the deformation-induced strain hardening

Grain growth has been investigated during heating of pure single-phase iron with an ultra-dispersed structure of different types under conditions which exclude retardation by impurity atoms or by dispersed particles. The rate of growth mainly depends on the type of boundaries formed in this structure during a preliminary treatment, which determines the different kinetics of primary recrystallization. The thermal stability of submicrocrystalline (SMC) structure increases with increasing degree of deformation. In contrast to the materials with an impurity and carbide retardation, in pure iron an intermediate annealing of the SMC structure, which usually leads during low-temperature recrystallization to the formation of a honeycomb structure, does not influence thermal stability. The formation of thermally activated centers of recrystallization has been found to occur during heating of iron with a uniform isotropic SMC structure at the temperature of the onset of the recrystallization of moderately deformed iron. The formation of a honeycomb structure does not lead to a considerable reduction in the accumulated strain energy, and, during further heating, thermally activated nuclei of recrystallization are formed.     

La2O3掺杂AgSnO2电接触材料的制备及性能研究

以Ag、Sn、La₂O₃粉为原料,采用机械合金法制备复合粉体。结合氧化法与粉末冶金工艺,对复合粉体进行氧化、压制、烧结。采用扫描电镜(SEM)和能谱仪、硬度计、金相显微镜、金属电导率测量仪等对复合粉体氧化前后的形貌以及电接触材料烧结前后的性能进行表征。结果表明：烧结后,电接触材料硬度较于烧结前明显下降。同时电接触材料随Sn含量增大,电阻率升高,密度反而下降。在一定的La₂O₃(0wt.%、0.75wt.%、1.5wt.%、2.25wt.%、3wt.%)含量范围内,La₂O₃掺杂量越高,密度越低。同时电接触材料经烧结后,随La₂O₃含量增加,其电阻率先降后升,在La₂O₃含量为0.75wt.%时,电接触材料的电阻率最低。     

Evolution of the structure upon heating of submicrocrystalline and nanocrystalline copper produced by high-rate deformation

Methods of electron microscopy, dilatometry, and microhardness and resistivity measurements have been used to study the effect of annealing on the process of recrystallization of a mixed submicrocrys-talline+nanocrystalline (SMC+NC) structure of 99.8% copper produced by high-rate (∼10⁵ s⁻¹) deformation using dynamic channel angular pressing (DCAP). It has been shown that the SMC+NC structure of copper is thermally stable upon heating to a temperature of 150°C. It has been found that the ρ/ρ⁰ ratio of copper with an SMC+NC structure at a temperature of 4.2 K is considerably (by 5 times) higher than ρ/ρ⁰ of copper in the annealed coarse-grained state. This effect is due to a high concentration of defects and a high degree of dispersity of the copper structure after DCAP. Changes in the microhardness and in the resistivity (at a temperature of 4.2 K) of the SMC+NC copper after annealing characterize the level of relaxation processes.     

Warm compacted NbC particulate reinforced iron-base composite(Ⅰ)--Effect of fabrication parameters

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Formation of Iron-aluminide Coating through Annealing of Shrouded Plasma-sprayed Iron/Aluminum Composite

The formation of iron aluminide coating was attempted through annealing of plasma-sprayed iron/aluminum composite deposit.Shrouded plasma spraying with nitrogen as protective gas was employed to prepare iron/aluminum composite coating using mechanically blended iron and aluminum powders with Fe/Al atomic ratio of 65:35.Annealing of the as-sprayed coating was carried out in argon atmosphere at 450,500,550,and 600 o C for different durations.The microstructure of the coatings was characterized by scanning electron microscopy and X-ray diffraction.The effect of annealing on the microstructure and phase evolution in the coatings was examined.The results show that iron/aluminum composite coating with low oxide inclusions and porosity is deposited by shrouded plasma spraying.It is found that Fe2Al5 intermetallics forms as an intermediate phase in the composite coating during annealing.As the annealing duration and temperature increase,iron aluminide intermetallic phases in the coatings increase and the microstructure becomes more homogeneous.After annealing at 600 o C for 336 h,FeAl and Fe3Al intermetallic phases will present in the coating as the main phases.     

Structure and properties of mechanically alloyed composite materials Al/Al-Cu-Fe quasicrystal

The structure and properties of metal-matrix Al/Al-Cu-Fe-quasicrystal composites produced by compacting mechanically alloyed powders have been studied. An increase in the time of mechanical alloying was found to lead to an increase in the microhardness. Compression tests showed that the failure of samples occurred via the intense formation of cracks along the direction parallel to the applied stresses; the ultimate strength increases with increasing time of mechanical alloying. As the compacting temperature increases, the ultimate strength remains unchanged to temperatures of 300–400°C; at higher temperatures, a marked increase in the ultimate compression strength is observed. An increase in the compacting temperature leads to an improvement of frictional characteristic of samples.     

铜包钢线加工工艺对其电阻率的影响

本研究采用包覆焊接法制备铜包钢线,并对其进行拉拔变形及退火处理。给出了经拉拔变形后的铜包钢线电阻率的计算公式。研究了不同的拉拔变形量和退火处理对其电阻率的影响;分析了其电阻率随加工工艺的变化规律。研究结果表明,铜包钢线的电阻率随其形变量的增加而升高。根据纯铜和钢丝原材料的电阻率,可计算经过不同拉拔变形量的导线的电阻率。随着铜包钢线退火时间的延长和退火温度的升高,其电阻率降低。通过实验数据分析,得到了铜包钢线的退火温度和退火时间分别与其电阻率关系的回归方程。