Papers by Keyword: Mechanical Milling

Abstract: Harmonic structured composites consist of a low fraction metal region like network and a dispersed another major metal region like island. The harmonic structured composites were produced via mechanical milling (MM) followed by spark plasma sintering (SPS), and its mechanical and thermal properties were investigated in detail. Microstructural observation of the MM powders and SPS compacts was achieved using scanning electron microscopy (SEM). The mechanical properties of the harmonic structured composites were evaluated using results of the Vickers hardness and the tensile tests. The thermal properties of a part of the harmonic structured composites were evaluated using results of thermo-mechanical analysis and laser flash method. High speed steel / mild steel harmonic structured composite exhibited high strength and enough ductility in spite of the trade-off relationship between strength and ductility. In addition, the high speed steel / mild steel harmonic structured composite also demonstrates a superior wear properties and low hardness simultaneously. On the other hand, molybdenum / copper harmonic structured composite demonstrate low coefficient of linear expansion and enough thermal conductivity compared to the conventional copper / molybdenum particle dispersed composite. The coefficient of linear expansion and thermal conductivity are the trade-off relation in this composite. In summary, the harmonic structure control is effective for improvement of the trade-off mechanical and thermal properties in the composite.

Abstract: The effect of complex high-energy action, including mechanical milling of Li₂CO₃-Fe₂O₃-ZnO initial reagents mixture and its consistent heating by the pulsed electron beam on solid-phase synthesis was studied by X-ray powder diffraction and thermal analyses. The initial mixture Li₂CO₃-Fe₂O₃-ZnO corresponds to the ferrite with stoichiometric formula: Li_0.5(1–x)Zn_xFe_2.5–0.5xО₄, where х = 0.2. The same studies were carried out with thermal heating in a laboratory furnace for detection the effect of radiation on the formation of phase composition lithium-zinc ferrite. Initial mixture was milled in AGO-2S planetary ball mill with a milling speed of 2220 rpm for 60 min. Radiation-thermal synthesis of the milled mixture was carried out by the pulsed electron accelerator (ILU-6) at 600°C and 750°C. The maximum time of the isothermal stage was 60 minutes. According to the X-ray powder diffraction and thermogravimetric analysis, it was found that the complex high-energy action leads to decrease a temperature and time of obtaining lithium-zinc ferrite homogeneous in phase composition. The proposed high-energy regimes allow to synthesized lithium-zinc ferrites at 600 °C for 60 minutes, which is much lower compared to conventional ceramic technology.

Abstract: This research is to analyze the effect of mechanical milling on the microstructure and mechanical properties of copper-iron. The sample is fabricated by compacting, milling and sintering processes. Sintering process is carried out using continuous type machine with conveyor belt mesh and the furnace type is muffle. After that, it is cooled with natural water jacket process. Vicker hardness testing and tensile strength test is performed to determine the mechanical properties of copper-iron alloys that occur. The mean value of sample 1 hardness (before milling) was 39.8 HV. The mean value of sample hardness 2 (after milling) was 74.9 HV. The value of the yield strength (σ) of sample 1 is 17.597MPa, and the value of ductility (ε) is 0.119. The value of the yield strength (σ) of sample 2 is 18.547 MPa, and the value of ductility (ε) is 0.073. The test results and analysis showed that by shrinking the size of metal powder, by milling for 2 hours, the hardness and yield strength of the product can increase. Although, the product becomes more brittle which is indicated by the decreased ductility value.

Abstract: This study reports on the elaboration and characterization of bulk nanocomposites samples obtained by dispersion of metallic powders at the nanoscale as reinforcements in a polymer matrix. Elemental Fe powders were successfully nanostructured via high-energy ball milling. Structural characterization of the produced powders was conducted using X-Ray Diffraction (XRD) analysis and Scanning Electron Microscopy (SEM). The Halder-Wagner approach was adopted to determine the powder’s average grain size, internal strain, lattice parameters and the mixing factors. Structural parameters evolution and morphological changes according to milling progression are discussed. Bulk nanocomposites samples were shaped in a home moulder by dispersion of coarse Fe and nanostructured Fe powders in a continuous matrix of commercial epoxy resin. The obtained bulk samples match the metallic X-band wave-guide WR-90 dimensions used for electromagnetic characterization. The two-port S_ij scattering parameters were measured via an Agilent 8791 ES network analyzer. The measured scattering parameters served to calculate the loss factor of samples and to extract the dielectric permittivity via the Nicholson-Ross-Weir conversion. Spectra evolution of the scattering parameters, the loss factor and the dielectric constant for epoxy resin with coarse Fe and nanostructured Fe reinforcements are commented.

Abstract: Some years ago a new process was developed for the elaboration of alloys in order to overcome drawbacks observed in samples produced by conventional casting. In the present work are shown the results obtained by high energy mechanical milling for Cu-Al-Ni. the mechanical alloying powder Cu₈₄Al₁₂Ni₄ (W%) was fabricated in high energy planetary ball milling at a speed of 250 r/min for various milling times (10 20 30 40 50 60 hours) the weight ratio of the balls of powder was 15 to 1. this mechanical alloying process is significantly modifying the characteristic of the powder, the recovered grains are ultimately compacted. The means used to study the different evolution are SEM Scaning Electron Microscopy, Differential thermal analysis DTA, X-ray Diffraction analysis and DRX in situ.

Abstract: Article presents an experimental study result of milling coarse strontium hexaferrite in beater mill with formation of magneto fluidized bed and without it. Magneto fluidized bed is formed by mutually perpendicular constant and alternating gradient magnetic fields. We studied the dynamics of particle size distribution from milling time and parameters of magnetic fields. Microstructure dynamics of strontium hexaferrite powder particles milled in various regimes was studied by X-ray diffraction methods. Milling efficiency and energy efficiency of milling process were studied in conditions with and without powder fluidization by magnetic fields. Analysis of experimental data showed advantages of milling in magneto fluidized bed in increased efficiency, particle size distribution homogeneity and powder chemical activity because of lattice micro-stresses.

Abstract: The current research represents one section of our studies concerning the improvement of the biocompatibility related to the biocomposite materials for bone grafts application. The submicronic/nanometric hydroxyapatite stands for the progress in biocompatibility. This study highlights the wet mechanical milling process and its effects on the morphological and thermophysical properties of the hydroxyapatite powder particles (30-50µm as raw material) obtained by this method (500 nm average). The scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) facility point out the morphological and chemical compositional features of the processed powders during 10 hours in dry argon atmosphere. The thermal analysis (TA) in argon atmosphere, too, reveals the influence of the milling parameters on the thermal effects generated by the processed hydroxyapatite powders. The experimental results of our research validate some milling mechanisms reported by the literature for wet/dry mechanochemical process conditions.

Abstract: We report a method to adjust the size of silica nanoparticles from silica sand. In this study, synthesized silica nanoparticles by sol gel process from silica sand were conducted, with previously was controlled the size of silica sand by mechanical milling. Silica sand was milled by High Energy Milling in order to reduce the size into powder form. Effect of milling time shown the content of sodium and silicon is increased in sodium silicate solution obtained from various times of silica sand milling (30, 60 and 90 minutes, respectively) which is reacted with sodium hydroxide 8 M. The result of silica nanoparticles from sol gel process of sodium silicate solution were characterized using atomic absorption spectroscopy, scanning electron microscopy and X-ray diffraction techniques. It was found that the size of silica nanoparticles could be tailored with the change of milling time.

Abstract: The alloy with the composition of Mg₂Ni prepared by low-temperature solid-phase sintering was mechanically milled for 10, 25, 40 and 50 h. The microstructures and electrochemical properties of the Mg₂Ni alloys were investigated by X-ray diffraction (XRD), optical microscope (OM) and electrochemical measurements. Furthermore, two broadening effects of XRD peaks caused by crystallite size and lattice strain were separated by the approximate function method and least square method. Crystallite size and lattice strain of the alloy were calculated. The results showed that sintered and milled alloys consist of the Mg₂Ni phase. The milled alloys transform partly into nanocrystalline/amorphous structures during the milling process. By calculation, the crystallite size decreases and the lattice strain in the alloy decreases first and then increases with increasing milling time. The discharge capacities of the sintered alloy are significantly improved by milling. The maximum discharge capacities of the milled alloys increase with the increasing milling time.

Abstract: Aluminium reinforced with different volume fractions of milled carbon fibres (MCFs) were manufactured via advanced powder metallurgy processing method. Composites containing 5, 10, 15 and 20 % volume fraction of MCFs were prepared using the Uniball magneto milling technique. Full density cylindrical compacts were produced by uniaxial hot pressing (UHP) at 600°C for a dwelling time close to 15 minutes. Characterization was done using x-ray diffractometry (XRD) and Field Emission Scanning Electron Microscopy (FSEM). The mechanical and physical properties were determined by compression testing, Vickers hardness, and Archimedes density. Unniball milling of blends resulted in decrease of aspect ratio of the MCFs and refinement of the Al grain size. Results show slight uniform distribution of MCFs in Al matrix for higher volume fractions without discernible porosity. In samples containing low volume fractions of MCFs (5% and 10%) fibres tended to be pushed towards grain boundaries during grain growth. In samples with higher volume fraction of MCFs (15 and 20% a more uniform distribution of MCFs in the product was obtained. The compressive strength of the composites was enhanced by the fibres, attributable to good interface bonding and wetting between the matrix and the reinforcement fibres. The combination of controlled ball milling and UHP techniques has facilitated the development of Al-MCFs composites potentially to be used in automobile industries.