Abstract

The work we have undertaken consists of preparing nanocrystalline Fe40Co60 powders by the Mechanical Alloying (MA) route. Characterization of obtained powders was applied on two steps. First, structural properties were investigated. X-ray Diffraction (XRD) was used to identify the formation of a disordered α (Fe40Co60) solid solution with a bcc lattice after 60h milling. By the Halder-Wagner approach lattice size, average grain size and residual strain were fixed. The morphology of milled powders was investigated by Scanning Electron Microscopy (SEM). Then bulk specimens were prepared by cold compaction for microwave measurements. Microwave dielectric permittivity and conductivity were determined using cavity perturbation technique. Microwave absorbing characteristic was measured according to line transmission method. Results obtained confirm that the developed structure after milling is the main factor that influences the microwave properties of nanocrystalline Fe40Co60 powders compared to elemental Fe.

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 Sij 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.

The objective of this work was to provide information about the behaviour of Fe-based nanocomposites when exposed to microwaves. It is about rectangular bulk samples of epoxy resin reinforced by nanocrystalline Fe powders and shaped in accordance to the internal section of the R100 metallic waveguide (8.2 to 12.4 GHz) at a fixed thickness of 7 mm. The nanocrystalline Fe powders were obtained by high-energy mechanical milling process using a planetary Retsch PM 400-ball mill. The milling speed was fixed at 200 rpm for three durations and the milling process were performed under Argon atmosphere. The bulk nanocomposites were obtained by dispersion of 30% vol. of the nanocrystalline Fe powders in the resin matrix. Electromagnetic parameters as complex relative dielectric permittivity and magnetic permeability, electric and magnetic loss tangent and reflection loss were calculated using reordered S parameters. The scattering parameters were characterized using a measure cell made off two metallic R100 wave-guides associated to an Agilent 8719 network analyser according to the reflection-transmission technique. The obtained spectra inform on the new electromagnetic properties as well as the absorption characteristic acquired by the bulk nanocomposites due to the presence of the nanocrystalline Fe powders.

The Al-Al 4 C 3 nanocomposite was produced via mechanical alloying of Al 6 wt% C mixture for a predetermined time (up to 20 h), followed by annealing. The structural evolution was characterised via X-ray diffraction and transmission electron microscope equipped with electron energy loss spectrometer. In addition, focused ion beam-scanning electron microscopy was used for locating and analysing the reinforcing particles. During milling, the size of aluminium particles reached the nanometre scale with a 54 nm size. After annealing, carbide was homogeneously distributed in the nanostructured aluminium particles with an average size of 50 nm, result in an average hardness of 320 HV. This was observed for the powder that was mechanically milled for 20 h and that underwent annealing from room temperature to 540°C and was maintained at this temperature for 4 h.