Properties of nanocrystalline copper prepared by vacuum-warm-compaction method

Nanocrystalline Cu with average grain size of 22.8-25.3 nm was prepared by vacuum-warm-compaction method. Scanning electronic microscope, HMV-2 type microhardness tester, X-ray diffractometer, and 6157 type electrometer were used to determine the microstructure, microhardness and electrical resistivity of as-prepared nanocrystalline Cu, respectively. The results show that the microhardness of nanocrystalline Cu increases with larger pressure, longer duration of pressure or higher temperature. The highest microhardness of nanocrystalline Cu is 3.8 GPa, which is 7 times higher than that of coarse-grained copper. The electrical resistivity of as-prepared specimens is (1.2-1.4)×10-7 Ω·m at temperature 233-293 K, which is 5-6 times higher than that of the coarse-grained copper.     

Novel preparation of big bulk-nanocrystalline Cu in large quantities

1 Introduction Bulk nanocrystalline(nc) metals, in which the grain is in nanometer range, often have some interesting properties such as increased hardness and strength, unique electronical and optical properties,which would open up a range of new applications[1, 2]. These remarkable mechanical properties of nc materials are highly desirable for structural application. To optimize the mechanical behavior, it is important to produce big-sized bulk nc metal materials in a way of lower cost and …     

Physical properties of selected brazing filler metals

Abstract

A suitable selection of the filler metal is vital for producing satisfactory brazed joints. The wettability of brazing alloys with base metals depends on physical properties such as surface tension, density, melting point, and viscosity. Thermal conductivity and electrical resistivity are also important since the filler metal is frequently required to have similar values to those of the base metal. In the present paper, the physical properties of liquid alloys relevant to brazing have been evaluated. Six different filler metal systems were analysed, comprising alloys based on Ag, Al, Au, Cu, Ni, and Ti. Results show that the viscosity values for most binary brazing filler alloys are of the order of 2–8 mPa s, with Cu and Al alloys exhibiting the lowest viscosities. The surface tensions of brazing alloys vary from 800 to 1800 mN m^-1, with the lowest surface tension values corresponding to the Ag and Al alloys. Thermal conductivity and electrical resistivity values fall in the range 10–200 W m^-1 K^-1 and 17–300 μΩ cm, respectively.     

Structure and microhardness of nanocrystalline composite alloys on the basis of Al and Ti

A nanotechnology for production of layered composite nanocrystalline Al-Si, Al(1Hf + 0.2Nb + 0.2Sn, wt %)-Si, Al(0.5Ce + 0.5Re + 0.1Zr, wt %)-Si, and Ti-Si alloys has been suggested. The structure of the nanocrystalline composites obtained has been studied by the methods of optical microscopy and scanning and transmission electron microscopy. Experimental data on the microhardness of layered composite nanocrystalline alloys on the basis of aluminum and titanium are given. The microhardness of the nanocrystalline two-layered Al-Si composite in comparison with submicrocrystalline aluminum increased by a factor of three. In the nanocrystalline two-layered Ti-Si composite (compacted from powders), the microhardness also increased by a factor of almost six in comparison with nanocrystalline titanium. In the nanocrystalline two-layered composite alloys of aluminum, the increase in microhardness in the case of the Al(Hf,Nb,Sn)-Si alloy was up to 45% as compared to the composite on the basis of the metallic foil and by a factor of two as compared to the powder-compact composite; and in the case of the Al(Ce, Re,Zr)-Si alloy, by a factor of 1.6 and 2.7, respectively. An increase in the number of layers in the composites had no significant effect on the level of microhardness.     

Cu和Fe大变形下的性能及Cu-Fe原位复合材料的强度计算

对工业纯Cu和纯Fe冷拔变形,研究大变形下性能与组织的变化。研究表明,在大变形的情况下,与退火态相比其抗拉强度、硬度和电阻率均有提高。纯Cu的抗拉强度、显微硬度和电阻率在截面真应变4.621时分别提高80.5%、42.5%和8.00%;纯Fe的抗拉强度、显微硬度和电阻率在截面真应变3.544时分别提高198.2%、54.4%和3.16%。随真应变的增大,Cu、Fe抗拉强度均明显增加,Fe表现的尤为突出。Cu的硬度和电阻率在应变增加到一定值后基本保持不变,而Fe的硬度和电阻率与抗拉强度一样始终随应变的增加而增加。用纯Cu和纯Fe在截面真应变3.544时的抗拉强度计算了Cu-11.5%Fe原位复合材料在相应变形下的抗拉强度,计算结果与测量值相符。     

硫代硫酸盐无氰镀银工艺及银镀层微观组织分析

采用硫代硫酸盐无氰镀银工艺,分别以 AgNO3和 AgBr 为主盐进行镀银。研究主盐含量、电流密度对Ag镀层表面质量、沉积速率和显微硬度的影响,并优化电镀参数。分析优化工艺下的Ag镀层结合强度和晶粒尺寸。结果表明：在AgNO3体系中,AgNO3最佳用量为40 g/L,最佳电流密度为0.25 A/dm2,制备的Ag镀层光亮平整,与基体结合良好,晶粒尺寸为35 nm。在AgBr体系中的最佳AgBr用量为30 g/L,最佳电流密度为0.20 A/dm2,与基体结合良好的Ag镀层的晶粒尺寸为55 nm。与AgBr体系相比,AgNO3体系适用的电镀电流密度范围较宽,制备的Ag镀层显微硬度高,晶粒尺寸小。     

Effects of intermetallic compound on the electrical and mechanical properties of friction welded Cu/Al bimetallic joints during annealing

Al/Cu metal joints applied for the electrical connector was joined by the friction welding method to limit the formation of intermetallic compound under optimum friction welding condition. To guarantee the reliability of the Al/Cu joints in service requirement, the effects of the intermetallic compound layer on the electrical and mechanical properties have been investigated under various annealing conditions. Two kinds of intermetallic compounds layer were formed in the joints interface and identified by AlCu and Al₂Cu. The growth kinetic of these intermetallics during the annealing can be followed by volume diffusion process. The activation energy of Al₂Cu, AlCu and total intermetallic compound (AlCu + Al₂Cu) represented 107.5, 98.42 and 110.22 kJ/mol, respectively. A thicker intermetallic compound layers could seriously degrade the electrical resistivity and tensile strength. The electrical resistivity with 21 μm thickness of intermetallic compound was 45 μΩ cm and increased to be 85 μΩ cm with 107 μm of intermetallic compound. Tensile strength remarkably decreased from 85 MPa to near zero at the annealing condition of 773 K and 129.6 ks and fracture occurred through the intermetallic compound layers.     

低温球磨制备块体纳米晶7050铝合金的组织和性能研究

采用低温球磨、热等静压和挤压等工艺制备了块体纳米晶7050铝合金。分别利用透射电镜(TEM)和扫描电镜(SEM)对制备铝合金的微观组织和断口形貌进行了观察,并对该铝合金的化学成分、密度、硬度和拉伸性能进行了测定。结果表明,制备的块体纳米晶7050铝合金的平均晶粒尺寸为100~200 nm,密度为2.76 g/cm3,HV显微硬度为1184 MPa。抗拉强度和延伸率分别为412 MPa和5.2%。经时效处理后,材料的拉伸性能虽有所提高,但仍低于传统7050铝合金。分析认为,由于雾化参数和球磨参数的选取欠合理,导致了薄片状粉体的产生。而薄片状的形貌又使得粉体不能有效充填包套,最终得到的块体材料致密度低,内部缺陷较多。这些缺陷使得块体材料内部的晶粒(或颗粒)之间形成弱界面连接,降低了材料的拉伸性能。     

液态Cu和Al的短程有序结构

为了研究液态Cu和Al的短程有序结构,建立了液态微观结构的纳米晶粒模型.根据这个模型,从晶体X射线衍射学的角度出发,通过对一定晶格结构的固态Cu和Al衍射峰进行宽化处理,计算出了它们的液态X射线衍射强度曲线.结果表明,这些强度曲线与实验获得的液态Cu和Al的X射线衍射强度曲线具有较好的一致性,这不仅证明了纳米晶粒模型的正确性,同时也证明了Cu和Al的液态短程有序结构分别是FCC和BCC.     

时效对铜铝钎焊接头界面化合物和性能的影响

采用Zn-22Al钎料对铜铝异种合金进行了火焰钎焊,并用加速老化试验模拟了其服役环境.研究了时效过程中铜铝钎焊接头界面化合物的形貌变化及其对铜铝钎焊接头电阻率和抗剪强度的影响,并对其生长规律进行了初步计算.结果表明,铜侧界面化合物在250℃恒温时效过程中不断变厚,其生长规律呈抛物线状,且其生长系数约为6.1×10-13cm2/s;当界面化合物的厚度为4.2μm和18.1μm时,铜铝接头的电阻分别为120.3μΩ和132.9μΩ,该界面化合物厚度对电阻率的影响系数为0.25;铜铝接头抗剪强度在时效过程中先有3%的上升,随后逐渐降低至接头初始值的85%.     

纳米晶体铜的制备及其结构表征

研究了纳米晶体铜材料的压制工艺条件对其相对密度和显微硬度的影响,并用正电子湮没寿命谱、扫描电镜和热重分析仪对其微观结构进行了表征。结果表明:压制压力越大,保压时间越长,样品的缺陷尺寸及数量减少,相对密度增加,显微硬度显著提高。随着压制压力的增大,缺陷类型的相对含量发生变化。而且纳米铜粉表面吸附的气体是纳米晶体铜样品内部缺陷的一个主要来源。     

Effects of noble metal addition on microstructure and thermoelectric properties of NaxCo2O4

The synthesis of Na_xCo₂O₄/Ag and Na_xCo₂O₄/Au composites was tried by mechanical milling and subsequent sintering. Ag and Au particles were added to the Na_xCo₂O₄ powder prior to the mechanical milling. The microstructure and thermoelectric properties of the Na_xCo₂O₄/Au composite were compared to those of the Na_xCo₂O₄/Ag composite and the Na_xCo₂O₄ single phase, and the effects of the Ag and Au addition on the thermoelectric performance of Na_xCo₂O₄ were discussed. Au particles around 2 μm or smaller in size, which were significantly smaller than Ag particles around 10 μm in size, were dispersed in the Na_xCo₂O₄ matrix. The Seebeck coefficient and the electrical resistivity of Na_xCo₂O₄ were slightly enhanced and significantly reduced by these noble metals addition, resulting in the large power factor of these composites. On the other hand, the Na_xCo₂O₄/Au composite showed the electrical resistivity larger than that of the Na_xCo₂O₄/Ag composite. Ag and Au addition markedly increased the thermal conductivity, and the dimensionless figure of merit of Na_xCo₂O₄ could not be improved by these noble metals addition.     

Dislocation contribution to modulus defect in nanocrystalline pure metals

The characteristic properties of dislocations in nanocrystalline pure metals are discussed in detail. It is considered that nanocrystalline metals prepared by inert gas condensation and compaction method or gas deposition method would contain dislocation densities equivalent to almost one dislocation in each grain, in general. Modulus defect expected from these dislocations is estimated to be roughly 1%. Further, a sensitivity of dislocation pinning effect to a number of point defects introduced in the specimen, is shown to be smaller by a factor of more than 10⁻⁶ in nanocrystalline metals, than in coarse-grained metals. These figures seem to be in reasonable agreement with recent results of low-temperature irradiation experiments.     

填充金属对钛合金与不锈钢电子束焊接的影响(英文)

采用Ni、V、Cu等填充材料进行钛合金与不锈钢的电子束焊接实验。采用光学显微镜、扫描电镜及X射线衍射对接头的微观组织进行分析。通过抗拉强度和显微硬度评价接头的力学性能,分析讨论填充材料对钛/钢电子束焊接接头微观组织和力学性能的影响。结果表明:填充材料有助于抑制Ti-Fe金属间化合物的产生。所有接头均由固溶体和界面化合物组成。对于不同的填充材料,固溶体和界面化合物种类取决于填充材料与母材之间的冶金反应。对于Ni、V及Cu填充材料,界面化合物分别为Fe2Ti+Ni3Ti+NiTi2,TiFe和Cu2Ti+CuTi+CuTi2。接头抗拉强度主要取决于金属间化合物的脆性。采用Cu填充金属的接头抗拉强度最高,约为234 MPa。     

Measurements of electrical and thermal properties with growth rate,alloying elements and temperature in the Al–Si–X alloys

In this work, effect of alloying elements (X = Cu, Co, Ni, Sb and Bi) and growth rates on the microstructure, physical properties (electrical resistivity, enthalpy and specific heat) of the directionally solidified Al–Si eutectic alloy have been investigated. Al–12.6Si–2X (wt. %) samples were prepared using metals of 99.99% high purity in the vacuum atmosphere. These alloys were directionally solidified under constant temperature gradient, G (7.80 K/mm) and different growth rates, V (8.3–166.0 μm/s). Flake spacing (λ) and electrical resistivity (ρ) were measured from the solidified samples. The variation of electrical resistivity with temperature in the range of 300–500 K for alloying elements in the Al–Si eutectic cast alloy was also measured. The enthalpy of fusion (ΔH) and specific heat (C_p) for the same alloy were determined by a differential scanning calorimeter from the heating curve during the transformation from solid to liquid.     

双相层状复合Cu-24%Ag合金的组织与性能

采用冷轧和时效工艺制备了Cu-24%Ag(质量分数)合金板材,研究了轧制过程中合金组织与性能的演变规律,讨论了合金强化和电导率与组织变化的关系。剧烈的轧制变形后,合金组织演变成Cu基体和Ag相交替排列的纳米层状结构,Cu基体中包含大量细小的Ag析出相纤维,一些Ag层区域分布着(Cu+Ag)共晶体。当变形至94%左右时,纵截面组织出现剪切带。随变形量增大,Cu基体和Ag层之间的相界面间距、Ag析出相纤维间距和共晶体片层间距均逐渐减小至几十纳米,强化效应显著增强,使合金的硬度在变形量大于96%时急剧增大。建立了Cu/Ag界面引起的电阻率增幅与变形量的关系,可以反映轧制变形引起的组织细化对合金电导率的影响规律。     

Al2O3/Al纳米复合材料的强化机制

将含氢等离子蒸发法制备的Al2O3/Al纳米复合粉体冷压成直径为25mm，厚度为2mm的块材，并通过620℃，40min热烧结和变形量为55％的冷轧形变处理使样品的相对密度达到99％。对官致密Al2O3/Al纳米复合材料的拉伸实验表明：其屈服强度σ0.2和断裂强度σb分别为粗晶Al的12－16倍和5－6倍，延伸率δ比同质冷轧粗晶Al约高28％。表征了Al2O3/Al纳米复合材料的结构和热稳定性，研究了晶粒细化的强化效应、非晶Al2O3弥散增强和冷变形加工硬化等对材料强度的影响。探讨了Al2O3/Al纳米复合材料的强化机制。     

溅射沉积Cu-Mo薄膜的结构和性能

用磁控溅射法制备含钼2.19%～35.15%(摩尔分数)的Cu-Mo合金薄膜,运用能谱仪(EDX)、X射线衍射仪(XRD)、透射电镜(TEM)、扫描电镜(SEM)、显微硬度仪和电阻计对薄膜成分、结构和性能进行研究.结果表明Mo添加使Cu-Mo薄膜晶粒显著细化,Cu-Mo膜呈纳米晶结构,存在Mo在Cu中的FCCCu(Mo)非平衡亚稳过饱和固溶体;随Mo含量的增加,Mo固溶度逐渐增加,而薄膜微晶体尺寸则逐渐减小,Mo的最大固溶度为30.6%.与纯Cu膜对比表明,Cu-Mo膜的显微硬度和电阻率随Mo含量的上升而持续增加.经200、400和650℃热处理1h后,Cu-Mo膜的显微硬度和电阻率均降低,降幅与热处理温度呈正相关;经650℃退火后,Cu-Mo膜基体相晶粒长大,并出现亚微米-微米级富Cu第二相.在Cu-Mo膜的XRD谱中观察到Mo(110)特征峰,Cu-Mo薄膜结构和性能形成及演变的主要原因是添加Mo引起的晶粒细化效应以及热处理中基体相晶粒的生长.     

Thermal evolution of high-purity and boron-doped sub-microcrystalline Ni3Al produced by severe plastic deformation

The influence of boron on the structural stability of sub-microcrystalline Ni₃Al intermetallic compounds was investigated by comparing a high-purity material with a boron-doped (0.1 wt%) compound. The nanocrystalline structure was obtained by severe shear deformation under quasi-hydrostatic pressure. Residual electrical resistivity, Vickers microhardness, X-ray diffraction and transmission electron microscopy were used to characterize the material evolution during thermal treatments in the temperature range 293–1313 K. After severe deformation the materials were disordered, with a small crystallite size of about 20 nm, similar in both materials. During isochronal anneals, the evolution of the microstructure, the long-range ordering and the recovery of the investigated properties took place at higher temperatures in the boron-doped compound, i.e. the thermal stability of the cold-worked structure was higher.     

Microstructures and Mechanical Properties of Electron Beam-Welded Titanium-Steel Joints with Vanadium,Nickel, Copper and Silver Filler Metals

Electron beam welding experiments of titanium alloy to stainless steel with V, Ni, Cu and Ag filler metals were carried out. The interfacial microstructures of the joints were examined by optical microscopy, scanning electron microscopy, and x-ray diffraction analysis. Mechanical properties of the joints were evaluated according to tensile strength and microhardness. The results showed that all the filler metals were helpful to restrain the Ti-Fe intermetallics formed in the Ti/Fe joint. The welds with different filler metals were all characterized by solid solution and interfacial intermetallics. And the type of solid solution and interfacial intermetallics were depended on the metallurgical reactions between the filler metals and base metals. The interfacial intermetallics were Fe₂Ti + Ni₃Ti + NiTi₂, TiFe, Ti₂Ag, and Cu₂Ti + CuTi + CuTi₂ in the joints welded with Ni, V, Ag, and Cu filler metals, respectively. The tensile strengths of the joints were primarily determined by the hardness of the interfacial intermetallics. The highest tensile strength was obtained in the joint welded with silver filler metal, which is about 310 MPa.