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Nanoquasicrystalline Al-based alloys show considerable promise for elevated temperature applications compared with commercial Al-based alloys. In particular, a group of Al-Fe-Cr-based alloys-containing Ti, V, Nb or Ta have outstanding thermal stability. In the present work, the elevated temperature mechanical properties of these nanoquasicrystalline alloys were studied by tensile tests at a constant strain rate. Tests were designed in order to compare the mechanical behaviour at different test temperatures. Fractographic analysis was also carried out. The apparent activation energy for plastic deformation was found to be close to that for lattice self-diffusion for pure Al in the Al-Fe-Cr ternary alloy and in the Ti-containing alloy, and for grain boundaries diffusion for pure Al in the V-containing alloy, whereas the activation energy of the alloy with Ta additions was three times higher. All of the alloys showed similar sensitivity of plastic deformation to the strain rate in the range of 10-3-5 × 10-6 s-1 at 350 °C. The apparent true stress exponent was napp ∼ 7, which can be associated with a deformation process controlled by dislocation mechanisms. © 2009 Acta Materialia Inc.

The amorphous state has been obtained in melt-spun Al90Fe5Nd5 and Al88FeNi6Nd5 alloy ribbons. Microstructural changes during annealing of these amorphous ribbons have been studied by differential scanning calorimetry, transmission electron microscopy, and X-ray diffratometry. The amorphous Al90Fe5Nd5 alloy crystallises through the primary crystallisation of fcc-Al phase from the amorphous matrix in the temperature range of 180–280°C, followed by precipitation of a metastable phase and of the equilibrium phases, Al11Nd3 and Al10Fe2Nd, in the temperature range of 330–380°C. A solid state transformation of metastable to equilibrium phases is observed at 540°C. In the Al88FeNi6Nd5 alloy, the primary phase fcc-Al crystallises in the temperature range of 200–290°C followed by the precipitation of Al3Ni and Al11Nd3 in the temperature range of 320–400°C.

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.

The development of new nanostructured and amorphous Al-alloys gives much hope to develop new improved light materials with high specific strengths and good corrosion resistance. In a previous work [1], the amorphicity range in Al-rich Al-Fe-Nb alloys produced by the melt-spinning technique was determined. In this work, the mechanical and corrosion behaviour of these alloys in the amorphous and partially amorphous states, is reported. The mechanical characterisation was carried out by microhardness and nanoindentation tests, the latter in order to determine Young's modulus. The corrosion behaviour has been evaluated by means of potentiodynamic polarisation techniques in a chloride containing solution. Results have been compared with those obtained for crystalline alloys with the same chemical composition. X-ray photoelectron spectroscopy (XPS) has been used to analyse the oxide film formed in melt-spun samples during the rapid quenching under air atmosphere. The Al-Fe-Nb fully amorphous alloys exhibit low Young's moduli, high microhardness values and a good corrosion behaviour.

The atomic structure and the glass-forming ability of amorphous Al-Fe-Nb have been explored in this study. The study has been carried out by means of scattering vector analysis of the structure factor obtained from X-ray spectra. The X-ray spectra show a pre-peak in the structure factor, which is attributed to chemical short-range order, together with the main amorphous peak. The average interatomic distances A1-Tm (Tm = transition metal) and Al-Al are shortened, and the strong interaction between Al and Fe must be responsible for the short-range order. The atomic size ratio criterion is discussed below, and it is proposed that the short-range order could be similar to the order of the quasicrystalline icosahedral phase in the Al-Fe-X alloys.

The aim of the work is to analyze the correlation between structure, shape and volume distribution of magnetic aggregates and magnetic properties in Fe x Cu 100- x ( x = 30, 50, 70) melt-spun ribbons. The structural analysis, performed by X-ray diffraction and scanning electron microscopy, shows that the sample is mainly composed of a mixture of Cu rich, non-magnetic, and BCC-Fe ferromagnetic aggregates widely distributed in size. Evidence of a partial mutual solubility between both immiscible elements is found in the as-cast state, so the main effect of the thermal treatment is to produce an almost complete segregation of both pure BCC-Fe and FCC-Cu immiscible phases, and thus, an increase in the corresponding mean grain sizes. The magnetization process of the samples reflects the complex magnetic behavior associated with a wide distribution in size of magnetic aggregates. The law of approach to saturation has been found to be an excellent complementary technique to correlate nanostructure and magnetic properties. The observed magnetic behavior can be interpreted as the contribution of superparamagnetic particles, single domain and multidomain aggregates, the multidomain being the first-order contribution. The results show that the shape of the magnetic aggregates governs through the internal demagnetizing field the macroscopic magnetization curve. This shape can be controlled through the Fe content, since as the Fe content increases the ferromagnetic aggregates evolve from spherical to ribbon-shaped.

The aim of this work is to contribute to the development of new, high specific strength Al alloys. Particularly, this research was focused on alloys with improved thermal properties so that they could withstand the subsequent compacting processes required for obtaining dense products without losing their properties. With this criterion the Al-Fe-Nb system was chosen. This paper presents the preliminary results concerning Al-rich Al-Fe-Nb amorphous and nanostructured alloys as well as their evolution with temperature.

Fe73.5Si13.5B9Nb3Cu1 powder particles have been obtained by gas atomization. Magnetization curves and coercivity were studied for particles ranging in size up to 1000 μm. The overall magnetic behavior of such material is a consequence of compositional heterogeneity of the microstructure as a whole. Anomalous temperature variation of coercivity (Hc) (i.e., a decrease in Hc with decreasing temperature) together with a decrease of saturation magnetization has been observed for less than 25 μm size. The origin of this behavior has been ascribed to metastable FeCu and FeNbSi phases in combination with an Fe-rich one. Making magnetic powders with coercive fields of the order of mOe remains a challenge for researchers. Our experiment has allowed us, at low temperature, achieving a coercive field of 9 Oe, much lower than those observed so far in this type of materials. This behaviour has been related with a FeCu phase present on grain boundaries. © 2013 American Institute of Physics.

Clear microstructural evidence is obtained from transmission electron microscopy of the occurrence of a modulated structure, as occurring in spinodal decomposition, during the decomposition of metastable mechanically alloyed Fe50Cu50 solid solutions and liquid quenched (Fe20Cu80)99B1.

Based on magnetic measurements, a modulated structure, as occurring in spinodal decomposition, has recently been suggested to exist in mechanically alloyed Fe-50 at.%Cu solid solutions after certain heat treatments. In this work, clear microstructural evidence of the modulated structure is obtained from transmission electron microscopy.

A ferromagnetic solid solution with a nominal atomic composition Fe70Cu30 and a body-centered structure has been obtained by high-energy ball milling. The decomposition of the system is monitored by X-ray diffraction (XRD), magnetic measurements and Mossbauer spectroscopy. According to XRD, for healing temperatures below 723 K there is only a bcc phase in the material, while for heating temperatures above 723 K a new phase, with a fcc structure, appears, suggesting that the solid solution has decomposed into bcc-Fe and fcc-Cu. However, the magnetic behavior observed during the decomposition process indicates that this evolution is more complex than the simple decomposition into the equilibrium phases. This behavior can be summarized in two points: (1) a decrease in the magnetization at 5 K, and (2) drastic changes in the coercive field with the thermal treatment, soft magnetic behavior for the material in the as-milled state, superparamagnetism for low heating temperatures and a hardening of the material heated to above 723 K, for which the values of the coercive field at room temperature are several times higher than those for the as-milled sample. The Mossbauer spectroscopy performed at room temperature shows that for the heat-treated samples the Fe atoms are in two different phases: a ferromagnetic phase, which evolves to bcc-Fe, and a paramagnetic phase.

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.

Experimental results corresponding to the saturation magnetization and coercive field during the decomposition, upon annealing, of bcc and fcc Fe_xCu_(1-x), obtained by mechanical alloying are reported. The overall behavior points out that the decomposition takes place in two steps: (i) at low temperatures a decrease of the saturation magnetic moment as well as an anomalous thermal dependence of coercive field are observed, however, no phase transformation is detected, and (ii) for further annealing temperatures a new phase appears; the magnetization tends to increase and the coercive field abruptly increases. The analysis of the results leads us to conclude that the first step corresponds to a spinodal decomposition. Fluctuations in the local composition give rise to coexistence of adjacent regions with Curie temperature varying continuously in a range of 1000 K across distances of a few nanometers, thus allowing the tailoring of the magnetic nanostructures.

Magnetic properties of equiatomic FeCu alloys, obtained by mechanical alloying, were measured in a temperature range between 5 and 300K. The as-milled sample consists of a metastable fcc FeCu phase with a temperature dependence of magnetization which follows a T 3 2 law. This metastable phase decomposes into Cu and Fe phases with annealing. After annealing at 820K, the magnetization value at low temperature is 30% smaller than the unannealed state. The Mossbauer spectrum obtained at room temperature shows a paramagnetic Fe phase with a relative resonant area of 30%. These results suggest that after this annealing process 30% of the iron is not in the ferromagnetic α phase but in a non-magnetic state (with vanishing atomic magnetic moment) or probably forming an antiferromagnetic γ-Fe phase (which is paramagnetic at room temperature).

Nanoquasicrystalline Al–Fe–Cr-based alloys have a microstructure composed of nanoquasicrystalline particles embedded in an α-Al matrix, and have high strength at elevated temperatures. However, the metastability of the quasicrystalline phase can limit the use of these alloys at elevated temperatures. The microstructure, stability and mechanical properties at different temperatures on melt-spun nanoquasicrystalline Al–Fe–Cr-based alloys containing Ti, V, Nb or Ta have been studied and summarized in the present work. The structural characterisation was carried out by means of X-ray diffraction, hot-stage transmission electron microscopy and scanning-transmission electron microscopy. The addition of a fourth element to the Al93(Fe3Cr2)7 alloy increases the thermal stability, in particular in the case of the Nb and Ta containing alloys, leading to the delay of the phase transformation towards the melting of the alloys. The mechanical properties at elevated temperatures were studied by tensile tests at different test temperatures with different pre-heat treatments. All the alloys showed a very high strength up to 350 °C, more than five times the strength of the commercial Al alloys. These values and the enhanced thermal stability achieved in the quaternary nanoquasicrystalline Al–Fe–Cr-(Ti, V, Nb or Ta) alloys make these alloys very promising for industrial applications. Fil: Galano, Marina. University of Oxford; Reino Unido Fil: Audebert, Fernando Enrique. University of Oxford; Reino Unido. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Grupo de Materiales Avanzados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: García Escorial, Asunción. Consejo Superior de Investigaciones Cientificas. Centro Nacional de Investigaciones Metalurgicas; España Fil: Stone, Ian C.. University of Oxford; Reino Unido Fil: Cantor, Brian. University of York; Reino Unido

The evolution of the microstructure and mechanical properties of an Al‐3 at%Cr‐0.3 at%Mo alloy was studied using centrifugally atomised powder and rod extruded from it. The powder showed different microstructures: cellular, globular or spherulitic, with dendrite rosettes, or mixed structures. The intermetallic A113(CrxMo1‐x)2 was present from the as‐quenched state and 0.36 at%Cr was retained as solid solution. In the finer powder the alpha phase solidified and the intermetallic then precipitated, forming spherulites. Hot extrusion did not damage the powder microstructure. Mechanical properties at room temperature were poor, but after annealing at 300 °C were better than in conventional alloys. Fracture occured in two different modes, depending on the material's heat treatment.

Melt-spun ribbons of Al-3at.%Cr, containing 1 at.% Ni and 0.3 at.% Mo respectively, were examined in the as-spun condition and after annealing. Al 13 Cr 2 and Al 3 Ni precipitates appear in the Al3Cr1Ni alloy, mainly with thermal treatments, the decomposition temperature being 430 °C. Meanwhile only Al 13 (Cr, Mo) 2 precipitation appears in the Al3Cr0.3Mo alloy and this decomposes at 420 °C.

It is well known that the saturation magnetostriction in nearly nonmagnetostrictive amorphous ribbons decreases with applied stress at a typical rate of 10-10 MPa-1. In this report we show by means of a simple experiment that a similar behavior is observed in samples constructed by piling up ribbons with high magnetostriction and opposite sign. A simple calculation points out that the strength of the stress dependence is governed by fluctuations in. It is concluded that zero magnetostriction may be reasonably achieved in Co-rich metallic glasses as a result of the coexistence of different magnetostrictive phases. © 1990 The American Physical Society.