On some physical properties of nanostructured Cu-Pb alloy prepared by mechanical alloying

Cu-Pb alloys have no solubility in the whole solid state and their physical properties are very different from each other. In the present study, nanostructured Cu-Pb alloy powders were synthesized by the mechanical alloying process, and their nanostructural characteristics were evaluated in order to elucidate the relationship between structure and properties. By appropriate control of mechanical alloying process variables, the Pb solid solubility in Cu matrix was increased up to 10 wt.%. The monotectic temperature of Cu-Pb alloy was also decreased by decreasing the crystalline size. The relation between the structure and properties of this nanostructured Cu-Pb alloy is discussed on the basis of the experimental results.     

The reaction of hydrogen with Mg-Cd alloys prepared by mechanical alloying

In this paper, we present the hydrogen storage properties of Mg-Cd alloys prepared by ball milling. Mechanical alloying of a mixture of Mg and Cd elemental powders containing up to 20 at.%Cd leads to a magnesium solid solution. The lattice spacings of the hcp Mg phase shrink with dissolution of cadmium atoms in Mg. The mechanically alloyed pure Mg-Cd alloys are very difficult to activate for hydrogen absorption. However, if vanadium and graphite additives are added, a Mg(Cd)-V-C nanocomposite forms after ball milling and the activation then becomes very easy. The hydrogen absorption/desorption kinetics are very fast. The plateau pressure and slope of hydrogen absorption/desorption increase, while the hydrogen storage capacity decreases with increasing cadmium content.     

Lead free solder alloys Sn-Zn and Sn-Sb prepared by mechanical alloying

The mechanical alloying (MA) processes of tin-9zinc (Sn-9Zn) and tin-5antimony (Sn-5Sb) were analyzed using an X-ray diffractometer, a differential scanning calorimeter (DSC) and a scanning electron microscope (SEM). The results showed that supersaturated solid solution and intermetallic compound were produced during the MA process. The size of powder particles could be controlled under the proper MA conditions and was reduced to 5 to 20 m. As a surfactant, proper addition of rosin allows MA to occur smoothly. However, it may also be a source of contamination of the metallic powder. It is considered that MA may be a technique analogous to casting to prepare solder alloys.     

Non-equilibrium W-Cu system alloy powder and bulk body prepared by mechanical alloying and shock compression

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

SnSb-Mo三元合金的电化学性能及其改性

以机械合金法制备了SnSb-Mo合金,并用XRD、SEM和EDS对合金的成分、组成及形貌等进行了分析;对合金材料的嵌脱锂性能研究发现,合金材料在最初的几次循环较好,但在随后的循环过程中容量迅速下降,通过SEM和EIS的分析发现影响合金材料循环性能的主要原因是合金材料与Cu基体之间的电接触.经过热处理后具有良好的嵌脱锂性能,首次嵌锂容量高达589mAh/g,经过20次循环之后仍具有451mAh/g的容量.     

Structure of nanocomposites of Al-Fe alloys prepared by mechanical alloying and rapid solidification processing

Structures of Al-based nanocomposites of Al-Fe alloys prepared by mechanical alloying (MA) and subsequent annealing are compared with those obtained by rapid solidification processing (RSP). MA produced only supersaturated solid solution of Fe in Al up to 10 at.% Fe, while for higher Fe content up to 20 at.% the nonequilibrium intermetallic Al₅Fe₂ appeared. Subsequent annealing at 673 K resulted in more Al₅Fe₂ formation with very little coarsening. The equilibrium intermetallics, Al₃Fe (Al₁₃Fe₄), was not observed even at this temperature. In contrast, ribbons of similar composition produced by RSP formed fine cellular or dendritic structure with nanosized dispersoids of possibly a nano-quasicrystalline phase and amorphous phase along with α-Al depending on the Fe content in the alloys. This difference in the product structure can be attributed to the difference in alloying mechanisms in MA and RSP.     

机械合金化制备Cu-Cr-C复合粉体

以Cu、Cr、C粉末为原料,采用机械合金化方法制备CuCr-C复合粉体,其中Cr、C的添加量按照Cr_3C_2质量分数为5%来计算;利用X射线衍射(XRD)和扫描电镜(SEM)研究机械合金化过程中粉末的物相和微观形貌,并结合能谱仪(EDS)面扫描得到粉末的元素微观分布。结果表明:随着机械合金化的进行,C、Cr和Cu形成Cu-Cr-C过饱和固溶体,随着球磨时间的延长,粉末粒径细化,颗粒形态由片状向球状发展;球磨30 h后,生成Cr_3C_2增强相,粉末细化趋势变缓并逐渐产生团聚,故原位生成Cr_3C_2的最佳球磨时间为30 h。     

机械合金化和粉末冶金法制备Fe-Mn-Si基形状记忆合金的研究进展

铁基形状记忆合金由于价格低廉、强度高、加工性能好、可焊接等优点引起广泛重视。机械合金化(MA)和粉末冶金(PM)作为制备材料的新工艺,可以用来制备性能优越的形状记忆合金。本文详述了机械合金化和粉末冶金工艺在制备Fe-Mn-Si基形状记忆合金过程中对合金相变、组织与性能的影响,以及此类合金在新领域的应用。最后提出了现阶段在研究MA/PM工艺制备Fe-Mn-Si基SMA中有关工艺参数、相变机制以及回复应力和低温应力松弛所存在的问题。     

Thermal and structural study of nanocrystalline Fe(Co)NiZrB alloys prepared by mechanical alloying

Three nanocrystalline alloys, Fe_75−x Co _x (Ni₇₀Zr₃₀)₁₅B₁₀ (x = 0, 10, and 20), were synthesized from elemental powders in a planetary high-energy ball mill. Their microstructure, magnetic properties, and thermal stability were characterized by X-ray diffraction, transmission M?ssbauer spectroscopy, transmission electron microscopy, scanning electron microscopy, induction coupled plasma, vibrating sample magnetometry, and differential scanning calorimetry. After 80 h of milling, the nanocrystallites size of alloys is in the range 6–10 ± 1 nm. The lattice parameter decreases when increasing (decreasing) milling time (Fe content). Furthermore, the thermal stability of the nanocrystalline phase increases when increasing Co concentration. The activation energy of the main crystallization process, between 275 ± 8 and 311 ± 10 kJ mol⁻¹, is associated with grain growth. Slight contamination from milling tools and milling atmosphere was detected. Minor differences were detected after M?ssbauer analysis.     

Thermoelectric properties of chromium disilicide prepared by mechanical alloying

CrSi and Cr_1?x Fe _x Si particles embedded in a CrSi₂ matrix have been prepared by hot pressing from CrSi_1.9, CrSi₂, and CrSi_2.1 powders produced by ball milling using either WC or stainless steel milling media. The samples were characterized by powder X-ray diffraction, scanning, and transmission electron microscopy and electron microprobe analysis. The final crystallite size of CrSi₂ obtained from the XRD patterns is about 40 and 80 nm for SS- and WC-milled powders, respectively, whereas the size of the second phase inclusions in the hot pressed samples is about 1–5 μm. The temperature dependence of the electrical resistivity, Seebeck coefficient, thermal conductivity, and figure of merit (ZT) were analyzed in the temperature range from 300 to 800 K. While the ball-milling process results in a lower electrical resistivity and thermal conductivity due to the presence of the inclusions and the refinement of the matrix microstructure, respectively, the Seebeck coefficient is negatively affected by the formation of the inclusions which leads to a modest improvement of ZT.     

溶融法和机械合金法制备Fe0．65Cr0．35-xVx合金的穆斯堡尔谱研究

通过机械合金法和溶融法制备了Fe0.65Cr0.35-xVx三元合金,采用X射线衍射、穆斯堡尔谱和振动样品磁强计(VSM)对其三元合金性质进行了研究.两种不同制备方法得到的样品均为体心立方(bcc)结构.采用二项式理论计算了的超精细磁场分布,并与实验值进行比对,在V高浓度时实验与理论值吻合地很好,这表明V原子可随机地占据Fe的bcc晶格位置;而当V原子浓度增加时,超精细磁场分布的实验值转移到低场处.引起它的原因可能有两种:(1) Fe-Cr系统比Fe-V系统进一步合金化更困难;2) Cr原子或Cr原子团簇形成近程有序.从平均每个Fe原子的磁矩随V含量的变化图中可以看出,随着V含量的增加,平均原子磁矩逐渐减小.     

Synthesis of nanocomposites and amorphous alloys by mechanical alloying

Mechanical alloying (MA) is a powder metallurgy processing technique that involves repeated cold welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Due to the specific advantages offered by this technique, MA was used to synthesize a variety of advanced materials. This article presents two specific examples of synthesis of nanocomposites containing a high volume fraction of the reinforcement phase in Al and TiAl matrices. It was possible to uniformly disperse 50 vol% of nanometric (50 nm) Al₂O₃ in Al and achieve high strength and modulus of elasticity. Similarly, it was possible to disperse 60 vol% of Ti₅Si₃ phase in the γ-TiAl intermetallic. Fully consolidated material showed superplastic behavior at 950 °C and a strain rate of 4 × 10⁻⁵ s⁻¹. Amorphous phases were produced by MA of blended elemental powder mixtures in several Fe-based compositions. From the systematic investigations carried out, it was possible to deduce the criteria for glass formation and understand the interesting phenomenon of mechanical crystallization. By conducting some controlled experiments, it was also possible to explain the mechanism of amorphization in these mechanically alloyed powder blends. Other examples of synthesis of advanced materials, e.g., photovoltaic materials and energetic materials, have also been briefly referred to. This article concludes with an indication of the topics that need special attention for further exploitation of these materials.     

Synthesis of nanocrystalline alloys and intermetallics by mechanical alloying

Nanocrystalline Al₃Ni, NiAl and Ni₃Al phases in Ni-Al system and theα, β, γ, ɛ and deformation induced martensite in Cu-Zn system have been synthesized by mechanical alloying (MA) of elemental blends in a planetary mill. Al₃Ni and NiAl were always ordered, while Ni₃Al was disordered in the milled condition. MA results in large extension of the NiAl and Ni₃Al phase fields, particularly towards Al-rich compositions. Al₃Ni, a line compound under equilibrium conditions, could be synthesized at nonstoichiometric compositions as well by MA. The phases obtained after prolonged milling (30 h) appear to be insensitive to the starting material for any given composition > 25 at.% Ni. The crystallite size was finest (∼ 6 nm) when NiAl and Ni₃Al phases coexisted after prolonged milling. In contrast, in all Cu-Zn blends containing 15 to 85 at.% Zn, the Zn-rich phases were first to form, and the final crystallite sizes were coarser (15–80 nm). Two different modes of alloying have been identified. In case of NiAl and Al₃Ni, where the ball milled product is ordered, as well as, the heat of formation (ΔH _f) is large (> 120 kJ/mol), a rapid discontinuous mode of alloying accompanied with an additive increase in crystallite size is detected. In all other cases, irrespective of the magnitude of ΔH _f, a gradual diffusive mode of intermixing during milling seems to be the underlying mechanism of alloying.     

Phase transformations in nanocrystalline alloys synthesized by mechanical alloying

The effect of nanometer grain size and extensive grain boundary regions in nanocrystalline alloy systems was investigated for the chemical order-disorder, structural, precipitation, and spinodal phase transformations. The kinetic paths for approach to the chemically ordered phase from the disordered phase in FeCo-Mo alloys were observed to be the same at different temperatures due to grain boundaries acting as short-circuited diffusion paths for atom movements. The structure of Fe₃Ge was bcc for small crystallite size and the equilibrium fcc phase developed only after a critical grain size was attained. This was understood as a manifestation of the Gibbs Thomson effect. The precipitation phase transformation in Fe-Mo alloys proceeded by a rapid movement and clustering of the Mo atoms to the grain boundaries that was correlated to the size of the nano grains, and subsequent formation of the Mo rich lambda phase directly in the grain boundary regions. The composition fluctuation domains for spinodal decomposition in nanophase Fe-Cr alloys were observed to be linearly correlated to the growth of grains.     

Synthesis of austenitic stainless steel powder alloys by mechanical alloying

Fe–18Cr–xNi (x = 8, 12, 13, 15, and 20 wt%) blended elemental powders were subjected to mechanical alloying in a high-energy SPEX shaker mill. The milled powders were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy and transmission electron microscopy techniques. It was shown that the sequence of phase formation in the Fe–18Cr–8Ni, Fe–18Cr–12Ni and Fe–18Cr–13Ni compositions was ferrite in the early stages of milling and then formation of austenite, which eventually transformed to stress-induced martensite on continued milling. The time for the formation of the austenite phase was shorter for the 12Ni and 13Ni powder blends than for the 8Ni powder. However, in the Fe–18Cr–15Ni and Fe–18Cr–20Ni compositions, the initial phase to form was ferrite and then a fully austenitic structure had formed on milling the powder for 10 h. No martensitic transformation occurred in this case on continued milling. The phase formation and microstructural features were confirmed by X-ray diffraction and transmission electron microscopy and diffraction techniques. A new metastable phase diagram was proposed outlining the stability of the austenite phase in ternary Fe–Cr–Ni alloys.     

Grain growth in nanocrystalline NbAl3 prepared by mechanical alloying

Grain growth and its kinetics were studied on an intermetallic compound, NbAl₃ powder prepared by mechanical alloying of elemental Nb and Al powders for 1.8 Ms in an argon atmosphere at ambient temperature. The initial and grown grain sizes were measured from the X-ray line broadening of as-alloyed and annealed powders. Isochronal annealing of mechanically alloyed powders from 573 to 1373 K indicated that substantial grain growth occurs only in a temperature range of 1048 to 1173 K and ceases at 1273 K regardless of anneal time. Accordingly isothermal annealing of 1.8 to 18 ks was carried out at 1048, 1073 and 1098 K to obtain the grain growth kinetic that is described by In (dD/dt) = In(r_o/3) –2.0 In D where D is the measured grain size and r _o a constant. This r _o depends on temperature according to r _o=r_o exp (– Q/kT) where Q is the activation energy for grain growth, k the Boltzmann constant and T the absolute temperature. Arrhenius plots of r _o against the reciprocal of temperature yield a straight line, from whose slope the activation energy for grain growth is deduced to be 162±2 kJ mol^–1. Of significance is the fact that the ultimate grain size at 1273 K is approximately 70 nm, which will not grow by further annealing even at 1373 K.On leave from Ibaraki University, Japan.     

Application of AFM to study functional nanomaterials prepared by mechanical alloying

Two-phase hard magnetic Nd₂Fe₁₄B/α-Fe nanocomposites and nanocrystalline TiFe electrode materials were prepared by mechanical alloying and heat treatment. The microstructure of both types of functional nanomaterials was investigated by atomic force microscopy. In the case of Nd₂Fe₁₄B magnetic phase, the microstructure refinement was realised by careful heat treatment and Zr addition. AFM investigations showed that Zr reduces a grain size of a parent alloy in the range of 20-40%. More than 90% grains have size below 50 nm, and more than 50% grains have size below 20 nm, which results in enhanced remanence. On the other hand, in TiFe alloy, a fine microstructure is known to improve greatly the properties of hydrogen storage alloys, when compared with their conventional polycrystalline counterparts. Additionally, the substitution of Fe by some amount of nickel improves the activation property of TiFe. Two types of AFM imaging modes, height and deflection, are accurate for agglomerate and grain size presentation, respectively.     

Synthesis and characterization of the novel nanostructured NiC carbide obtained by mechanical alloying

In the present work, a comprehensive study of mechanical alloying of Ni-carbon nanotubes (CNT) and Ni-Graphite equiatomic powder mixtures under the same technological modes has provided to reveal the features of using different types of carbon (CNT or graphite) as a charge component. The as-milled powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and magnetometric study. A novel nanoscale fcc NiC monocarbide was synthesized regardless the type of the charge used. According to the XRD study the formation of this phase takes place in two stages. A two-step carbide formation mechanism has been proposed. The associated changes in the nickel lattice, such as changes in the lattice parameter, lattice strain and residual stresses, which led to the formation of NiC monocarbide were also evaluated and discussed. Parameters of the electronic structure of NiC were calculated using the MStudio MindLab 7.0 software package with the experimental data on the crystal structure of the NiC phase obtained as input. Temperature dependencies of magnetic susceptibility of NiC synthesized have been studied up to 950 K. Carbides synthesized were found to be weak ferromagnets at the room temperature and their Curie temperature T_C ranges within 670 – 725 K. The calculated value of the magnetic moment per nickel atom (2.83μ_B) is higher than that of a bulk Ni (1.3μ_B). Likely, the observed increase of μ is caused by the presence of a certain amount of residual single-domain ferromagnetic Ni nanoparticles in the samples synthesized.