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Different studies carried out in the last three decades on the magnetic susceptibility of the spinel ZnFeO ferrite have revealed the positive character of its Curie–Weiss temperature, contradicting its observed antiferromagnetic behavior which is characterized by a well-defined susceptibility peak centered around the Neel temperature (10 K). Some approaches based on ab initio calculations and mixture of interactions have been attempted to explain this anomaly. This work shows how for very low values of the inversion parameter, the small percentage of Fe atoms located in tetrahedral sites gives rise to the appearance of ferrimagnetic clusters around them. Superparamagnetism of these clusters is the main cause of the anomalous Curie–Weiss behavior. This finding is supported experimentally from the thermal dependence of the inverse susceptibility and its evolution with the degree of inversion.

Synthesis and processing methods can have a significant influence on the physical properties of spinel zinc ferrite since it can produce microstructures characterized by different microstructural parameter such as the arrangement of the ions, lattice parameter, crystallite size and lattice strains (or microstrain). In this work, it has been evaluated the magnetic properties of samples prepared by ceramic synthesis, sol-gel and a third one provided by a ceramic powder supplier. Later, the synthesized samples have been ball-milled for 50 h and compared with a sample prepared by mechanochemical synthesis during 150 h. X-ray powder diffraction (XRD) analysis, performed in order to understand the relation between microstructure and magnetic properties, showed that these four materials are characterized by different values of the microstructural parameters (lattice constant, inversion degree and crystallite size). It was concluded that cation inversion is the most important parameters that can be effective in the deviation of the magnetic properties of zinc ferrite from the properties of the bulk form. Finally, the magnetization curves for the samples milled for 50 h were very similar to the sample prepared by mechanochemical, as expected from the similar microstructural parameters obtained from their XRD patterns. The inversion degree for these samples varied from 0.56 to 0.61 with saturation magnetization at 5 K around 79.0 emu/g. Although structural and chemical properties of this material can be selected by a proper choice of the preparation method, it is also possible to obtain the same microestructural and magnetic properties by a thermomechanic process, regardless of the synthesis method used.

Containerless processing of droplets and drops by atomization and electromagnetic levitation are applied to undercool metallic melts and alloys prior to solidification. Heterogeneous nucleation on crucible walls is completely avoided giving access to large undercoolings. Experiments are performed both under terrestrial (1 g) conditions and in reduced gravity (µg) as well. Microgravity conditions are realized by the free fall of small droplets during atomization of a spray of droplets, individual drops in a drop tube and by electromagnetic levitation of drops during parabolic flights, sounding rocket missions, and using the electro-magnetic levitator multi-user facility on board the International Space Station. The comparison of both sets of experiments in 1 g and µg leads to an estimation of the influence of forced convection on dendrite growth kinetics and microstructure evolution.

We report a study of the structure-processing-property relationships in a high strength AlFeCrTi nano-quasicrystalline alloy and composites containing 10 and 20 vol% ductilising pure Al fibres. The superimposed contributions of several different strengthening mechanisms have been modelled analytically using data obtained from systematic characterisation of the monolithic alloy bar. An observed yield strength of 544 MPa has been substantiated from a combination of solid solution strengthening, work hardening, precipitation hardening and Hall-Petch grain size dependent effects. These materials have been shown by other authors in previous published work to be highly sensitive to the size distribution of particles in the powder from which they are made, and the subsequent thermomechanical processing conditions. The processing condition employed in this study provided micron-sized grains with a strong [111] preferential orientation along the extrusion direction and a bimodal size distribution of the icosahedral nano-quasicrystalline precipitates. Both were deemed to be a significant contributor to the high yield strength observed. The addition of pure Al fibres was found to decrease the yield strength linearly with increasing Al content, and to augment the ductility of the composites.

Long-term effect of plasma electrolytic oxidation (PEO) coatings on in vitro corrosion of 3D Mg implant specimens has been investigated in simulated body fluid (SBF). Hydrogen evolution rate in PEO-coated specimens was 35 times lower compared to the non-coated alloy during first 2 weeks of immersion (0.04–0.07 mL cm d) and reached a steady-state rate of 0.3 mL cm d by week 6 of immersion. Studies of the tribocorrosion behaviour of the PEO-coated alloy disclosed that the coatings rapidly lose their tribocorrosion resistance due to hydration of the coating material and associated drastic decrease of microhardness but exhibit a better tirbocorrosion performance than the non-coated material.

Aluminium alloy powder having a nominal composition of Al93Fe3Cr2Ti2 (at%) has been prepared using gas atomisation. The atomised powder present a microstructure of an aluminium matrix reinforced with a spherical quasicrystalline icosahedral phase, in the range of nanometre in size. The powder was consolidated into bars using warm extrusion. The microstructure of the extruded bars retains the quasicrystalline microstructure and the bars present outstanding mechanical properties, i.e. proof stress of 280 MPa at 300 °C. Upon heating the microstructure evolves towards the equilibrium. The thermal evolution was investigated by means of x-ray diffraction, differential scanning calorimeter, scanning electron microscopy and transmission electron microscopy. According to these observations a transformation in two steps is proposed. A first step consists in the decomposition of the supersaturated solid solution of the matrix and the quasicrystals, and a second step in the transformation of the quasicrystals into the equilibrium phases.

© 2015 Elsevier B.V. All rights reserved. Bulk Al93Fe3Cr2Ti2 bars extruded from gas atomised powder particles present a microstructure of an aluminium matrix reinforced with a spherical nanoquasicrystalline phase. In this work the evolution of the microstructure of Al93Fe3Cr2Ti2 extruded bars upon heating at 400 °C for up to 1000 h is investigated by means of X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. According to our observations we propose that the quasicrystalline alloy evolves in two steps: a first step consists in the decomposition of the supersaturated solid solution of the matrix and the quasicrystals, and a second step in the transformation of the quasicrystals into the equilibrium phases.

© 2014 Elsevier Ltd. All rights reserved. Density functional calculations, using the SIESTA code, have been performed for determining the influence of short range order, SRO, on the magnetic properties of Ni75Al25 (at%). Calculations have been performed on a supercell formed by eight cells in the fcc L12 structure that corresponds to a number 24+n of Ni atoms and 8-n of Al atoms, where n measures the deviation to the ordered L12 structure composition. Three values of n were considered, 0, 1 and -1. It turns out that the electronic density of states at the Fermi level, the magnetic moment and the susceptibility strongly depend on the value of n. Magnetic measurements and structural characterization were carried out before and after annealing particles of Ni75Al25 at% composition, with size below 25 ¿m, obtained by gas atomization process. The as atomized samples exhibit a broad distribution of Curie temperatures that reflects SRO fluctuations. After annealing the distribution width drastically decreases and noticeable modi fications in the magnetic properties, as Curie temperature and magnetic moment, are observed. Since annealing keeps roughly constant the composition, these modifications should be attributed to the thermally induced increase of SRO. The influence of chemical short range order, CSRO, determined by X-ray diffraction, on the experimental magnetic properties is discussed on the light of the density functional calculations. The remarkable controversial values of the magnetic properties found in the literature can be well understood within the framework of the analysis reported below.

Las aleaciones Al93Fe3Cr2Ti2 (at%) preparadas por atomización con gas y, posteriormente, consolidadas por extrusión en forma de barras presentan una microestructura de una matriz de aluminio reforzada con una fase cuasicristalina que les confiere unas magnificas propiedades a elevadas temperaturas, con resistencia mecánica de 250 MPa a 300ºC. Los cuasicristales son cristales sin periodicidad traslacional, observados por primera vez por Shechtman en 1982. La estructura cuasicristalina es metaestable y tiende al equilibrio por lo que el estudio de su estabilidad térmica es de gran importancia para sus aplicaciones industriales. En este trabajo se analiza la transformación de esta microestructura con los tratamientos térmicos mediante las técnicas de difracción de rayos x, calorimetría diferencial de barrido, microscopía electrónica de barrido y microscopía electrónica de transmisión. Se propone que la transformación tiene lugar en dos pasos. En el primero tendría lugar la descomposición de la solución sólida sobresaturada, tanto en la matriz como en los cuasicristales, y en el segundo tendría lugar la transformación de los cuasicristales en las fases de equilibrio del sistema.

In this work, the dependence of the coercive field of Fe73.5Si13.5B9Nb3Cu1 gas atomized powder with the temperature for different particle sizes has been studied, observing an anomalous behavior in the under 25 powder particle size fraction. This unusual behavior is related with the microstructure of the powder, and is attributed to the presence of a multiphase magnetic system, with non-magnetic regions decoupling the ferromagnetic domains.

Magnetization curves of mixed Nb and FeSi based micrometric particles have been analyzed. The influence of the dispersion of Nb particles on the mixture remanence and coercivity has been studied above and below the Nb superconducting critical temperature. The hysteresis loop shows, at 5 K and low applied fields, a decrease of both remanence and coercivity with respect to the one of pure ferromagnetic powders as well as a stair like profile. These features are explained as a consequence of the diamagnetic hysteresis loop of Nb giving rise to local stray fields acting on the ferromagnetic particles at its nearest neighboring. © 2012 American Institute of Physics.

In this work, thermalevolution of bulk nanoquasicrystalline Al93Fe3Cr2Ti2 material, obtained by consolidation of nanoquasicrystalline powder particles, is studied. The powder particles were obtained by gas atomization and the consolidation of the powders was achieved via warm extrusion [1] and [2]. The evolution of the microstructure during processing as well as with further thermal treatments was investigated. The consolidated material contains spherical particles of an icosahedral i-phase of around 200 nm in diameter. The quasicrystalline phase is detected even after 1 h at 500 °C, and afterwards, it evolves through a metastable Al6Fe phase to the equilibrium phases

Nanocrystalline powder of Fe–Si–B–Cu–Nb has been obtained by means of mechanical milling of the corresponding nanocrystalline ribbons. Gasatomization technique has been used to minimize the magnetic hardening due to stress effects observed in ball-milled samples. Fe–Si–B–Cu–Nb and Fe–Si nanocrystalline samples have been prepared by gasatomization. The aim of our work is to analyse the particle size dependence of coercivity in this nanostructuredalloys and to show the analogies and differences between ball-milled and gas atomized samples

In this work, solution heat treatments at different temperatures were performed in a commercial based AA7050 aluminium alloy, with and without titanium addition, produced by mechanical alloying and hot extrusion with the aim to investigate the effect of titanium addition and mechanical alloying in the precipitates stability. The same heat treatment conditions were used in a reference sample obtained from a commercial AA7050 alloy. Solution heat treated samples were characterised by differential scanning calorimetry (DSC), optical microscopy and hardness test. Once the better temperature for the solution treatment of modified alloys was defined, the ageing curve at 120°C was obtained to verify the effect of milling and Ti addition in the precipitation and in the maximum values of hardness obtained for the alloys.

After 80 h of milling the elemental powders, mechanical alloying of Al 90Fe5Nd5 produces a nanostructured composite, which consists of nanocrystals of fcc-Al and some Al11Nd3 precipitates, embedded in an amorphous matrix. This composite has a Vickers hardness of 2.8 GPa and is thermally stable up to about 340 °C. Above this temperature it decomposes into Al11N3 and Al 90Fe2Nd5 phases.

Wires of composition Cu-15 vol%Fe, consisting of a Cu matrix and a body-centered cubic (BCC) Fe phase of fiber morphology have been prepared from rapidly solidified powders by extrusion and heavy cold drawing. Upon cold working, the thickness of the Fe ribbons decreases to 3.5 nm while the ribbon width drops to 27 nm. Thermal dependence of magnetization exhibits a decrease with temperature markedly faster than in bulk BCC-Fe. This dependence is found to arise from the confinement of low-energy spin waves due to the elongated shape of Fe nanoribbons. © 2003 Elsevier B.V. All rights reserved.

Tensile properties of PM2124aluminiumcompositesreinforced with Ni3Al, NiAl, Cr3Si and MoSi2 intermetallic powder particles have been investigated in tempering conditions T1 and T4. Intermetallics were produced by self-propagated high-temperature synthesis and composite powders consolidated by extrusion. 2124/MoSi2 showed the highest thermal stability, and the best mechanicalproperties even after comparison with those of 2124/SiC composite after processing through the same route

Aluminum-based alloys with a mixed structure consisting of a nanometric-scale dispersion of Al particles embedded in an amorphous matrix can present excellent values of tensile strength without detriment of ductility. Also, the mechanical properties of bulk aluminum alloys processed by powder metallurgy are found to improve when the powders are obtained by rapid solidification techniques, such as gas atomisation. In the present work we report on the preparation of a novel alloy powder of the Al-Fe-Nd system obtained by gas atomisation, aiming to obtain amorphous or new metastable phases and to study their potential possibilities as precursors for the production of bulk aluminium-based high strength alloys. Amorphous and metastable phases have been observed in the powders with the smaller size range, but multiple stage crystallisation was detected by DSC in all size ranges. The smaller size powders showed a temperature interval of 120°C between the first and second peak of crystallisation which is very adequate for consolidation without crystallisation of intermetallic phases.

Al-5Cu-5Zr alloys prepared by three different non-equilibrium processes, such melt-spinning, inert gas atomization and mechanical milling have been mechanically and microstructurally characterized. Melt-spinning and ball milling processes introduced a high degree of metastability in the material, which presented a high hardness even after thermal treatment at high temperature. On the other hand, the inert gas atomization process failed to introduce metastability in the material.

Alloying and amorphization of ball-milled samples of nominal composition Fe100-xSix (x = 5-50) has been investigated by means of X-ray diffraction, scanning electron microscopy, differential scanning calorimetry and magnetic measurements. An evaluation is made of the relative quantities of phases present in the as-milled samples. © 1991.

The formation of both an amorphous Fe-Si phase and a crystalline solid solution of Si in Fe was demonstrated through differential scanning calorimetry (DSC), X-ray diffraction, and thermomagnetic measurements of ball-milled pure-element powders. X-ray results are inconclusive about the effective alloying of Fe and Si and about their amorphization, although they seem to be compatible with both facts. Partial amorphicity of as-prepared samples seems to be related to the irreversible exothermic peaks observed at 195°C on DSC thermograms. This is confirmed by comparing X-ray diffractograms of thermally treated samples with those of untreated material. Also, an anomaly in the thermomagnetic behavior which is not related to any transformation present in the equilibrium phase diagram was observed at 200°C.

A mixture of Fe and Si powders (3:1 in atomic proportion) has been milled for different periods of time in a planetary ball mill. Investigations of the microstructure and properties of the materials so prepared were performed using XRD, SEM, DSC and VSM techniques. Evidences about the partial formation of the solid solution Fe75Si25 as well as about the amorphous structure of the as-milled material were found.