High-energy Mechanical Alloying Research Articles

Formation of a nanodispersed metal-matrix structure during a combined high-energy mechanical alloying of powders of aluminum-based SiC-containing alloys

Phase and structural state of composite materials produced by combined mechanical alloying of the AK12M2 and D16 powder alloys with silicon carbide in high-energy planetary mills with the use of ball charging and quasi-cylindrical bodies have been studied. It has been found out that the type of bodies substantially affects the mutual solubility of components in the systems investigated, as well as the perfection of the crystal lattice of the material treated, and its adhesion to the bodies and to the inner surface of the drum. It is shown that the use of balls favors an enhanced mutual solubility of the components and stipulates higher deformation of the crystal lattice of the product in comparison with the quasi-cylinder grinding bodies. The differences observed are discussed based on the calculated data obtained earlier for the ratio of normal and tangential components of energy consumption for different types of grinding bodies.

Effect of the leaching of Ru-Se-Fe and Ru-Mo-Fe obtained by mechanical alloying on electrocatalytical behavior for the oxygen reduction reaction

In the present work, Ru-Se-Fe and Ru-Mo-Fe alloyed nanoparticles were synthesized from high purity powders (Ru, Se and Mo) by means of the high-energy mechanical alloying. Fe was integrated to the alloys because of the erosion of the mill balls. The ORR electrocatalytic performance of the alloys (lixiviated or not) was evaluated in a rotating disc electrode (RDE) at room temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for the structure characterization of the materials. Small-particle clusters with granular morphology and nanometric sizes were obtained in all the cases. According to the Tafel parameters from the RDE results, a first order ORR is present in both electrocatalytic systems through a 4e − global multielectron transference to form water: O 2 + 4H + + e − → H 2O. The electrocatalytic activity showed that the mechanical alloying enabled to obtain nanoparticle electrocatalysts with good ORR performance. Lixiviation of the mechanical alloying powders not improves the catalytical responses.

How Fe<sub>60</sub>Co<sub>40</sub> and Fe<sub>72</sub>Al<sub>28</sub> Nano-Alloys Produced by Mechanical Alloying Behave when Exposed to Microwaves

Fe60Co40 and Fe72Al28 nano-alloys were synthesized from elemental powders via highenergy mechanical alloying. The prepared samples were characterized using X-ray diffraction, scanning electron microscopy and X-band waveguide to measure the reflection loss in a frequency range of 9-10 GHz. The XRD patterns show that disordered Fe60Co40 solid solution with a bodycentred cubic structure is formed for milling times longer than 12 h, and after 4h milling, the solid solution Fe72Al28 has been largely formed. Morphological studies indicate an average grain size of 10 to 15 nm. The microwave- absorbing characteristic reveal good performance for Fe60Co40 compared to Fe72Al28, the maximum reflection loss is about -12 dB for the absorber.

Effect of Metal Additives (Co and Ni) on the Electrochemical Properties of Lithium/FeS<sub>2</sub> Batteries

Iron, sulfur and transition metal powders were used as the starting materials to prepare iron disulfide (FeS2) cathode material at room temperature by high energy mechanical alloying. Modified FeS2 were also prepared by incorporation of transition metals like Co and Ni. Li/FeS2 cells with the prepared iron disulfides as cathodes were studied for discharge properties at room temperature using the 0.5M LiTFSI in tetra(ethylene glycol) dimethyl ether (TEGDME). The first discharge capacities of Li/composite FeS2 cell with 5 wt.% Co and 3 wt.% Ni were 571 and 844 mAh/g, respectively, compared to 389 mAh/g for the cell without any additive. The enhanced properties resulted from the better electronic conductivity of the material containing the metallic additive. The initial capacity and cyclic performance were improved when nickel and cobalt were added to prepare the modified iron disulfide.

Structural and magnetic characterization of composite YCo5/α-Fe (20 wt%) powders prepared by mechanical alloying and subsequent annealing

Powder mixtures of YCo5+α-Fe (20wt%) were prepared by high energy mechanical alloying under Ar using a SPEX 8000 mill and subsequent vacuum annealing. The structural and magnetic properties were investigated by X-ray diffraction, DSC, and magnetic measurements. After 4h of milling, the alloyed powders were found to be composed of an amorphous Y–Co phase and α-Fe with a mean grain size strongly reduced. The DSC curves exhibited an irreversible broad exothermic peak with a maximum at 555°C associated with the crystallization process. Subsequent high vacuum annealing in the temperature range 550–750°C led to the formation of rhombohedral Th2Zn17-type and α-Fe(Co) phases. Samples were magnetically soft showing low remanence and room temperature coercivity in the range 470–800Oe. The latter is in agreement with the low magnetocrystalline anisotropy along the basal plane exhibited by the Y2(Co,Fe)17 phase.

High-energy ball-milling synthesis and densification of Fe–Co alloy nanopowders by field-activated sintering (FAST)

Nanocrystalline Fe–Co soft magnetic alloy powders also containing approximately 4% Cr and 1% V were prepared by high-energy mechanical alloying in liquid media (hexane). Bulk nanostructured magnets of 40 mm diameter were obtained by field-assisted sintering (FAST) also known as spark-plasma sintering (SPS). We used a FAST furnace type HPD25-1 (FCT Systeme, Rauenstein, Germany). The FAST method was shown to successfully assist in decoupling densification from microstructural coarsening, mainly due to the limited exposure of the alloy nanopowders to high temperatures during their sintering into nanostructured bulk compacts. Results of chemical and microstructure analysis by SEM/EDX are presented to evidence the achievement of uniform microstructures and absence of composition gradients across sintered bulk specimens in spite of their large size.

Production and Characterization of Aluminium NbAl<sub>3</sub> Composite by Mechanical Alloying and In Situ - A Process Comparison

This work analyses the production of Al based composites with particulate reinforcement, via mechanical alloying. Composites were produced by mixing Al and NbAl3 powders by high energy mechanical alloying, under liquid nitrogen atmosphere, followed by cold pressing and hot sintering; and by controlling NbAl3 phase precipitation in liquid Al (in situ formation of the reinforcement). Results on composite produced from powders showed better distribution and incorporation, besides finer dispersion of particles in the matrix when mechanical alloying is employed. In this case, high dispersion on particulate phase was found despite predominance of small particles; there are no evidence of interface formation. When composites are produced by in situ formation of NbAl3 intermetallics, results showed that the formation of the reinforcement directly from the liquid matrix and the peritectic reaction between NbAl3 and liquid Al, provide a perfect reinforcement/matrix interface. Products showed good mechanical properties, good wear behavior and reduced thermal expansion.

Physicochemical Characterization of Mixed RuO2−SnO2 Solid Solutions

Mixed SnO2−RuO2 oxides were prepared by high-energy mechanical alloying of various proportions of pure SnO2 and RuO2 powders. The physicochemical characterization of the resulting materials was conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical surface analysis. It is shown through XRD analysis that a single-phase (tetragonal) (Sn−Ru)O2 solid solution is formed over the whole composition range, in which the Sn4+ and Ru4+ ions share the same cationic sub-lattice of the rutile-like structure. The surface of the compounds was analyzed by XPS and shows a deficit of Ru atoms, with [Ru]surface = 36 at. % for an equimolar SnO2−RuO2 concentration in the bulk of the sample. In the case of pure nanocrystalline RuO2, the total surface charge, qT*, the most easily accessible surface charge, qO*, and the less easily accessible surface charge, qI*, are 35.3, 29.0, and 6.3 mC cm-2 mg-1, respectively. These surface charges vary linearly wi...

SHS of Ti 3SiC 2: ignition temperature depression by mechanical activation

The influence of high-energy mechanical alloying on the self-propagating high-temperature synthesis (SHS) of titanium silicon carbide (Ti 3SiC 2) was investigated. A depression of the SHS ignition temperature as a function of milling time was observed. After 107 min of milling, a spontaneous combustion reaction (MASHS) occurred within the milling vial at 67 °C, which corresponded with an 25 °C rise in the vial temperature. Observed changes in the microstructure of the milled powders gave considerable insight into the process, which provides a means of controlling a previously difficult synthesis procedure.

Preparation and optical characterization of hydroxyapatite and ceramic systems with titanium and zirconium formed by dry high-energy mechanical alloying

Calcium phosphate-based bioceramics, mainly in the form of hydroxyapatite, Ca 10(PO 4) 6(OH) 2—HAP, is the main mineral constituent of teeth and bones with excellent biocompatibility with hard and muscle tissues. These materials exhibit several problems of handling and fabrication, which can be overcome by mixing them with a suitable binder. The dry milling process of fabrication of HAP presents the advantage that melting is not necessary and the powder obtained is nanocrystalline. The high efficiency of the dry milling process opens a new way to produce commercial amount of nanocrystalline HAP and others bioceramic. In this work dry mechanical alloying has been used to produce nanocrystalline powders of HAP using three different experimental procedures (HAPA: Ca(H 2PO 4) 2 + Ca(OH) 2; HAPB: Ca(H 2PO 4) 2 + CaCO 3; and HAPC: CaHPO 4 + CaCO 3). HAP was obtained after 5, 10 and 15 h of milling in the reactions HAPA and HAPB, but it is necessary 15 h of milling in the reaction HAPC to obtain HAP. In order to improve the mechanical properties of HAP calcium phosphate ceramics, with titanium (CaP-Ti) and zirconium (CaP-Zr), have been prepared by dry ball milling using two different experimental procedures: CaP-Ti1: Ca(H 2PO 4) 2 + TiO 2; CaP-Ti2: CaHPO 4 + TiO 2; and CaP-Zr1: Ca(H 2PO 4) 2 + ZrO 2, CaP-Zr2: CaHPO 4 + ZrO 2. The calcium titanium phosphate phase, CaTi 4P 6O 24, was obtained in the reaction CaP-Ti1. In the reactions CaP-Ti2, CaP-Zr1 and CaP-Zr2, it was not observed the formation of any calcium phosphate phase even after 15 h of dry mechanical alloying. The milled HAP and the ceramics systems obtained were characterized by X-ray powder diffraction, infrared and Raman scattering spectroscopy.

Investigation of rheological properties of mechanically alloyed and turbula processed composite powder PIM feedstock by capillar rheometer

In this study, Fe-Cr-Al2O3-Ti-Y2O3 powders, used for superalloy production, were milled in a high energy mechanical alloying attritor and processed in a ball containing turbula mixer with a threedimensional action for 1, 2, 10, 24 and 48 h. The effects of milling process and time on mean particle size, distribution and morphology were analysed by SEM and a laser particle size analyser. Mechanically alloyed and turbula mixed composite powders were then mixed with a polyethylene based binder to obtain PIM feedstock. The flow behaviour of the powder feedstock was investigated by capillary rheometer at temperatures between 155 and 200°C. It was found that, increasing the milling time resulted in spherical shaped particles in the attritor and flakelike particles, with a reduced particle size, in the turbula mixer. Attritor milling led to the feedstock flowing more easily and better results for PIM, whereas turbula mixed powders were found not to be suitable for PIM because of the flakelike structure.

ＭｇＢ２超伝導材料の現状と展望

Recent studies on MgB2 superconductors are reviewed. MgB2 single crystals show Bc2 anisotropy factors of 2.6—4.5. The Bc2 of a single crystal at 4.2 K is ∼15 T when the field is parallel to the ab plane. MgB2 bulks, wires and tapes show a higher Bc2 than single crystals. This Bc2 enhancement can be explained by the introduction of defects that decrease the coherence length. MgB2 thin films show a much higher Bc2 than bulk materials. The highest Bc2, 49 T at 0 K, was reported for highly resistive MgB2 thin film. One of the effective pinning centers in MgB2 seems to be grain boundary. Effective pinning centers are also introduced by nanometer-size impurity additions such as SiC. SiC addition significantly increased Jc values in the high field regions, and hence Birr. Most tapes and wires are now fabricated by a powder-in-tube (PIT) method. The ex-situ PIT method employs MgB2-reacted powder and hard sheath materials such as stainless steel. The Jc of ex-situ tapes sensitively depends on the packing density of the MgB2 core. A maximum Jc of ∼4.5×105 A/cm2 is obtained at 4.2 K and zero fields. Ex-situ processed tapes show Jc anisotropy with respect to the field orientation due to the grain alignment. The in-situ PIT method employs a powder mixture of Mg and B. High-energy ball milling and mechanical alloying of the starting powder mixture enhanced the Jc values. The replacement of MgH2 with Mg is effective for improving the reactivity and enhancing Jc values. The Jc at 4.2 K and zero magnetic field reached 2—3×106 A/cm2. The highest Jc, 2.5×104 A/cm2, was obtained at 10 T and 4.2 K when SiC was added to in-situ processed tape prepared with MgH2+B powder. This Jc is comparable to that of a commercial Nb-Ti conductor.

High-energy mechanical alloying of thermoplastic polymers in carbon dioxide

High-energy ball milling was performed on low density polyethylene (LDPE) and isotactic polypropylene (iPP) as well as on 20/80 binary mixture of both polymers. Mechanical alloying was carried out at high pressure with carbon dioxide for a short period. The presence of CO2 avoids oxidative mechano-chemical degradation of polymers and enhances the effectiveness of the milling. The effects of the mechano-chemical treatment on the molecular and physical properties of both single polymers and blends of intrinsically incompatible polymers were explored by FTIR spectroscopy, thermal analysis, intrinsic viscosity determination and solvent fractionation. Structural changes on PP and PP/LDPE blend were observed and have a strong dependence on the milling time. Mechanical tests confirm an overall improvement in blend properties by mechanical alloying. Experimental evidences are presented to suggest that CO2 high-energy ball milling causes a self-compatibilization of the blend LDPE–iPP by breaking iPP polymer chains and allowing them to recombine with the neighboring LDPE chains.

The Fabrication of Near Net-Shaped Hydroxyapatite Ceramics by the Oxidation of Solid, Metal-Bearing Precursors

Near net-shaped bodies of hydroxyapatite (HA), Ca10(PO4)6(OH)2, have been fabricated by a novel process: the oxidation of solid, metal-bearing precursors. High-energy mechanical alloying was used to produce an intimate powder mixture of metallic calcium and calcium pyrophosphate, β-Ca2P2O7, that possessed an overall stoichiometry consistent with HA (molar Ca:Ca2P2O7 ratio = 4:3). The milled Ca-Ca2P2O7 mixtures were sufficiently malleable as to allow for compaction and forming (pressing, machining) into shaped green bodies with relatively high densities (80-86%). The green bodies were converted into phase-pure HA through heat treatments at 500-600°C in dry oxygen (for Ca oxidation), 850°C in moist oxygen or air (for HA formation), and 1100-1150°C in moist oxygen or air (for sintering). The offsetting volume changes associated with calcium oxidation (Vm(CaO) < Vm(Ca)) and subsequent HA formation (Vm(HA) > 4Vm(CaO) + 3Vm(Ca2P2O7)) resulted in HA bodies that retained the shapes and dimensions (to within a few percent) of the metal-bearing precursors.

TEM Study of Nanocrystalline AgxNi1-x Solid Solutions

Abstract Research on nanocrystalline materials, a new class of materials with a grain size of less than 20-30 nm in diameter, has flourished in the last decade because of their unique properties and Characteristics. While enormous amounts of nanocrystalline intermetallic alloys have been made by high energy mechanical alloying, little of this research has been carried out to study the formation of alloys of very low solid solubility elements such as Ag and Ni (0.1 at % at 750 °C).Upon quenching atoms in a state of high mobility, they can be “frozen” into unconventional random positions and thermodynamically metastable or unstable phases can be formed. This research was thus undertaken to synthesize nanocrystalline AgxNi1-x solid solution because fiber composites of this system have been widely used in low-voltage electrical circuits. This paper presents a TEM/AEM investigation of the traditionally immiscible nanocrystalline AgxNi1-xsolids formed by gas evaporation - vapor quenching method.

High energy ball-milled Ti2RuFe electrocatalyst for hydrogen evolution in the chlorate industry

The high energy mechanical alloying of a Ti–Ru–Fe powder mixture (atomic ratio 2 : 1: 1) has been performed by extensive ball-milling in a steel crucible. The structural evolution of the resulting materials has been studied by x-ray powder diffraction analysis. The identification of the various phases present in the materials, as well as the crystallite size and strain, has been performed by Rietveld refinement analysis. In the first stage of the material transformation, Ru or Fe atoms dissolved into Ti to yield to the formation of β–Ti. Upon further ball-milling, almost all the original constituents of the powder mixture have disappeared and a new simple cubic Ti2RuFe phase is formed, with a crystallite size as small as 8 nm. The electrochemical properties of these materials have been tested in a typical chlorate electrolyte by cold-pressing the powders into disk electrodes. At 20 h of ball-milling, where the phase concentration of Ti2RuFe reaches 96%, a reduction of the activation overpotential at 250 mA cm−2 of nearly 250 mV is observed when compared to that of a pure iron electrode.

High energy mechanical alloying of aluminium-titanium powders by planetry ball mill: S. Saji et al. (Osaka University, Suita, Osaka, Japan). J. Japan Inst. of Metals, vol 59, no 2, 1995, 183–190. (In Japanese.)

High energy mechanical alloying of aluminium-titanium powders by planetry ball mill: S. Saji et al. (Osaka University, Suita, Osaka, Japan). J. Japan Inst. of Metals, vol 59, no 2, 1995, 183–190. (In Japanese.)

Giant magnetoresistance in bulk mechanically alloyed Co-Ag

Bulk granular magnetic solids have been prepared by the high-energy mechanical alloying of fine cobalt and silver powders, with cobalt concentrations of 5, 15 and 30 at.%. The threshold for giant magnetoresistance in the parent samples was found to lie between 5 and 15 at.% Co, with a maximum effect of 12% at 4 K in the 30 at.% Co sample. The effect of the mechanical alloying process parameters, such as the milling energy, milling time and annealing, on the magnitude of the GMR in this system was also investigated. The sub-micron scale homogeneity of the samples was found to vary with the milling energy, with completely homogeneous samples produced after milling at high energy, and only 60% homogeneity levels achieved in the sample milled at a lower energy. The isotropic and anisotropic contributions to the total magnetoresistance were separated experimentally, and the linear relationship between the two (derived for an ideal superparamagnetic system) was observed experimentally.

A novel and simple route to catalysts with a high oxygen storage capacity: the direct room-temperature synthesis of CeO2–ZrO2solid solutions

High-energy mechanical alloying of pure CeO2 and ZrO2 at room temperature results in the formation of a single phase Ce1–xZrxO2 fluorite structured solid solution in all the examined composition ranges; the compounds are characterized by a high oxygen storage capacity and an excellent reducibility.

Reaction synthesis of MoSi2 from high purity elemental powders

This paper reports that Molybdenum disilicide (MoSi{sub 2}) is an intermetallic compound that combines a high melting point (2293K) with excellent resistance to high temperature oxidation. With respect to mechanical properties the behavior of polycrystalline MoSi{sub 2} falls into one of three regimes, based on the sue temperature: t {lt} 925{degrees} C: strong + brittle; 925 {lt} T {lt} 1250{degrees} C:strong + ductile and T {gt} 1250{degrees} C:weak + ductile. The majority of recent investigations have focused on the properties of MoSi{sub 2}-based materials processed from commercially available powder. Commercial MoSi{sub 2} powder contains significant amounts of oxygen; for example, a chemical analysis of powder obtained from Cerac Inc. revealed an oxygen content of 0.6 wt%. Consolidation of such powder resulted in a substantial volume fraction of amorphous silica in the final product. MoSi{sub 2} powder produced by the crushing and grinding of arc-melted elemental Mo and Si also exhibited amorphous Si-rich particles after vacuum hot-pressing at 1973K and 30MPa. Grinding of the cast material to powder was done in ethanol but one this was driven off, the powder was air-handled. The high energy mechanical alloying in an argon atmosphere of elemental Mo and Si powder to produce MoSi{sub 2}more » has also been investigated. Following hot pressing, the MoSi{sub 2} made in this fashion still contained a substantial volume fraction of SiO{sub 2}.« less