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Aluminum matrix composites reinforced with Al–Ni intermetallic compounds and Al 2 O 3 were obtained by hot pressing of high-energy milled powders. Using the reaction between Al and NiO and aiming to preserve part of the Al content after completing the reaction by increasing the relative amount of Al, composites containing Al 2 O 3 and Al–Ni intermetallic compounds were produced. These composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Depending on the Al/NiO molar ratio, the reaction can be activated either during milling or during subsequent hot pressing. Hence, two different processing routes can be used to produce such composites. Starting from powder mixtures with an Al/NiO molar ratio of 15/3, the reaction took place during milling, forming Al 3 Ni and Al 3 Ni 2 plus Al 2 O 3 reinforced Al composite powder, which was consolidated by hot pressing. An Al/NiO molar ratio of 20/3 prevented the reaction from occurring during milling, but enabled it to occur during subsequent hot pressing, forming the same reinforcement phases. The reactive-milled composite is harder and presents higher porosity than the reactive-sintered ones, after consolidation by hot pressing under the same parameters. In the latter route, the longer the milling time prior to hot pressing, the smaller the size of the reinforcement phases.

Deformation-induced crystallization is correlated with thermal-induced crystallization in alloys with different compositions in a single amorphous alloy system. In Al87Y6Ni5Co2 and Al85Y8Ni5Co2 alloys, which undergo primary crystallization during heating, deformation-induced crystallization of fcc-Al has been observed. In Al83Y10Ni5Co2 alloy, which undergoes eutectic-like crystallization, no deformation-induced crystallization was observed. These observations can be explained by the presence or absence of quenched-in nuclei and the work required for the creation of an amorphous/crystalline interface under compressive stress.

In the present work, the glass forming ability (GFA) and its compositional dependence on Al-Ni-Ce system alloys were investigated as a function of several thermal parameters. Rapidly quenched Al 85 Ni 15-x Cex (X=4,5,6,7,10), Al 90 Ni 5 Ce 5 , Al 89 Ni 2.4 Ce 8.6 , Al 80 Ni 15.6 Ce 4.4 and Al 78 Ni 18.5 Ce 3.5 amorphous ribbons were produced by melt-spinning and the structural transformation during heating was studied using a combination of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results showed that the GFA and the thermal stability in the Al-rich corner of Al-Ni-Ce system alloys were enhanced by increasing the solute content and specifically the Ce content. © 2008 Elsevier B.V. All rights reserved.

Amorphous alloys present exceptional values of mechanical strength but lack any significant plasticity at room temperature. Deformation of amorphous alloys occurs in shear transformation zones that connect to form shear bands, which are easier to deform than the surrounding matrix, thus facilitating further deformation in the same location of the specimen. However, the presence of particles dispersed in the amorphous matrix can modify such strain softening behavior, resulting in real plastic deformation before fracture. Also, depending on the type of particles and how they are introduced, they can modify the crystallization behavior of the amorphous matrix by acting as heterogeneous nucleation sites. In this context, this paper reports on the effects of the addition of SiC particles on the crystallization of Al 84 Ni 8 Co 4 Y 3 Zr 1 amorphous ribbons. Pre-alloyed ingots with and without added SiC particles were melt-quenched into amorphous ribbons by the single-roller melt-spinning technique and then selectively and partially crystallized at the first and second crystallization temperatures, as determined by differential scanning calorimetry. Primary crystallization of nanometric-sized fcc-Al crystals was found to occur in both ribbons (with and without added SiC), confirming that crystallization reactions were not altered by the ceramic particles. Aluminum carbide (Al 4 C 3 ) crystals resulting from high-temperature liquid metal/SiC reactions were observed as coatings on the SiC particles and as isolated particles dispersed in the amorphous solid matrix. In both cases, the Al 4 C 3 particles also did not change the crystallization behavior of the amorphous Al 84 Ni 8 Co 4 Y 3 Zr 1 matrix, since no heterogeneous nucleation of fcc-Al crystals was observed.

A thermodynamic approach to predict bulk glass-forming compositions in binary metallic systems was recently proposed. In this approach, the parameter γ * = Δ H amor /(Δ H inter − Δ H amor ) indicates the glass-forming ability (GFA) from the standpoint of the driving force to form different competing phases, and Δ H amor and Δ H inter are the enthalpies for glass and intermetallic formation, respectively. Good glass-forming compositions should have a large negative enthalpy for glass formation and a very small difference for intermetallic formation, thus making the glassy phase easily reachable even under low cooling rates. The γ * parameter showed a good correlation with GFA experimental data in the Ni–Nb binary system. In this work, a simple extension of the γ * parameter is applied in the ternary Al–Ni–Y system. The calculated γ * isocontours in the ternary diagram are compared with experimental results of glass formation in that system. Despite some misfitting, the best glass formers are found quite close to the highest γ * values, leading to the conclusion that this thermodynamic approach can be extended to ternary systems, serving as a useful tool for the development of new glass-forming compositions. Finally the thermodynamic approach is compared with the topological instability criteria used to predict the thermal behavior of glassy Al alloys.

Despite, the homogeneous and refined microstructure, spray-formed deposits of binary Fe–Si alloys with high silicon content are still difficult to hot/cold roll due to A2-disordered/B2-ordered reactions. The addition of aluminum to Fe–Si alloys may be able to keep the A2-disordered phase metastable at temperatures below 973 K, allowing the deposits to be rolled without cracking while adequately maintaining their magnetic properties. This study is a first attempt to investigate the microstructure and the magnetic properties of spray-formed Fe–3 wt.%Si–3.5 wt.%Al alloy. Argon and nitrogen were used as atomization gases. The addition of aluminum to Fe–Si alloys led to the successful production of thin sheets (0.5 mm thickness) from spray-formed deposits when using argon as atomizing gas. In contrast, the use of nitrogen led to the formation of AlN particles, resulting in excessive brittleness of the spray-formed deposit, which fractured during cooling to room temperature. Otherwise, the magnetic properties of the Fe–3.0 wt.%Si–3.5 wt.%Al alloy performed very well when compared with binary Fe–6.5 wt.%Si, especially when spray formed with argon.

The microstructure and the tensile properties of an spray co-deposited Al-8.9 wt.% Si-3.2 wt.% Cu-0.9 wt.% Fe + (Al-3 wt.% Mn-4 wt.% Si)p composite was investigated after extrusion and heat treatment. The composition of the AlMnSi p alloy was selected aiming to improve the formation of α-Al(Fe,Mn)Si instead of β-Al(Fe,Mn)Si intermetallic. The spray formed deposits were extruded at 623 K and heat treated to peak aged (T6) condition. Room temperature tensile tests of the spray formed and extruded/heat treated alloy showed significant increase of elongation to fracture when compared with the values observed for the as-spray formed deposits, >10% and

In this study the Fe63Nb10Al4Si3B20 (at.%) alloy was processed by spray forming with the aim of investigate the formation of amorphous phases and novel microstructures by the high cooling rate involved in this process. The gas/metal mass flow rate used was 0.25, and nitrogen was used as the atomization gas. The resulting deposit of a mass of about 1.2 kg, as well as the overspray powder, with a median particle diameter about 120 μm, were characterized by using X-ray diffractometry, differential scanning calorimetry and scanning and transmission electron microscopy with energy of dispersive spectroscopy. Magnetic properties were measured through hysteresis loop tracer equipment. The overspray powder presented a mass median diameter of d50 ≅ 120 μm and an increasing of amorphous phase volume fraction with decreasing of particle size. The microstructure of the deposit was heterogeneous varying with the thickness, presenting at center region 20 mm and at border 1 mm with different porosities 5 and 10%, respectively. The thicker region presented fully crystalline microstructure whereas the thinner presented about 75% amorphous phase. The phases identified in both deposit and overspray powder were: amorphous, α-Fe, Fe23B6, FeB and FeNbB. Amorphous phase formation in the thinner region of the deposit and the absence in the thicker region indicates that the resulting amorphous phase depend on the maintenance of amorphous phase formed during atomization that might be controlled by process parameters. Spray forming of Fe-based amorphous alloys followed by hot consolidation in T

The microstructure and the tensile properties of an Al–8.9 wt.% Si–3.2 wt.% Cu–0.9 wt.% Fe–0.8% Zn alloy processed by spray forming was investigated. The porosity level, the conditions of the heat treatment applied and the presence/addition of certain alloying elements to this alloy is known to greatly affect its mechanical properties. In this work, the alloy was gas atomized with argon and deposited onto a copper substrate, extruded at 623 K and heat treated to the T6 temperature Mg was added to some heats. Room temperature tensile tests of the spray formed and extruded alloy showed significant increase of elongation when compared with the values observed for the as-spray formed deposits. This result can be ascribed to the decrease of porosity promoted by the extrusion process. The spray formed and extruded, T6 heat-treated samples showed significant increase of strength without lowering the elongation results. The addition of 0.3 wt.% Mg increased the response to the heat treatment process.

Aluminum additions to brittle Fe–6.5 wt.% Si alloys made possible the mechanical processing of these alloys at lower temperatures and thus being determinant in the development of the texture. The aim of this work was to analyse the evolution of the crystallographic texture of a spray-formed (SF) Fe–6.5 wt.% Si–1.0 wt.% Al during rolling operation for thin sheets production. The SF deposit was warm-rolled and then air cooled to obtain partial recrystallisation. The initial texture (0 1 1) [ 0 1 ¯ 1 ] [1 0 0] (// to normal direction-ND) of the deposit was changed to approximately (0 1 3) [ 1 1 ¯ 0 ] [1 1 0] (8° from ND) after the last reduction step. The maxima intensities of texture was found at 700 °C (89% of reduction) showing the influence of rolling temperature; after warm-rolling the entire texture changes to a partial ND fibre running from {0 0 1} to {1 1 0}, with negligible Goss intensities. The transition away from an ND fibre texture in the lattermost case (99.5% reduction) was in turn associated with the near-absence of shear bands.

In the present work Fe 73− x Nb x Al 4 Si 3 B 20 ( x = 5, 10) alloys have been processed by melt-spinning with the aim of studying the crystallization sequence through annealing in suitable temperatures. Melt-spun ribbons were characterized by differential scanning calorimetry (DSC), X-ray diffractometry (XRD) through Cu-Kα ( λ = 1.54 A) and synchrotron radiation ( λ = 1.77 A) and transmission electron microscopy (TEM). Soft magnetic properties were measured through the hysteresis loop tracer. In-situ XRD through synchrotron radiation was very accurate in phase identification. Fe 73− x Nb x Al 4 Si 3 B 20 ( x = 5, 10) alloys showed the possibility of forming ferromagnetic amorphous alloys composed of commercial Fe-based master alloys with fine nanocrystalline structure and good soft magnetic properties.

In the Ni–Si system, the eutectic structure composed of Ni–Ni3Si presents inherent thermal stability, allowing composite materials to be obtained with well-aligned and finely dispersed microstructures. The work reported here consisted of an investigation into the microstructure and morphology of such a eutectic alloy from the standpoint of its growth conditions. A Ni–Si eutectic alloy was processed by applying the directional solidification method at low growth rates and the rapid solidification technique using a melt-spinning process. The results indicate that samples processed under conditions close to equilibrium show a regular and aligned microstructure, while rapid solidification leads to an anomalous microstructure and the formation of a metastable phase.

The glass former Fe 83 Zr 3.5 Nb 3.5 B 9 Cu 1 (at.%) alloy was processed by spray forming. The aim was to investigate the possibility of forming novel microstructures using this process. The ratio between the gas mass flow rate and the metal mass flow rate used was 0.23, and nitrogen was used as atomization gas. The resulting deposit, weighting about 0.8 kg, as well as the overspray powder with a median particle diameter about 150 μm, were characterized by using X-ray diffratometry, differential scanning calorimetry and scanning electron microscopy with energy dispersive spectroscopy. Saturation induction ( B s ), maximum permeability ( μ max ) and coercive field ( H c ) were measured. The overspray powder showed a microstructure consisting of amorphous and α-Fe phases. The volume fraction of the amorphous phase decreased as the granulometric size range increased. The deposit presented fully crystalline structure with α-Fe, Fe 3 Nb, Fe 2 Zr and Fe 2 B phases. The formation of amorphous phase in the overspray and its absence in the deposit indicates that the deposit was formed by the impacting of a high volume fraction of fully liquid droplets, providing temperature and time enough for complete crystallization of the deposit.

The microstructure and the tensile properties of an Al–8.9 wt.% Si–3.2 wt.% Cu–0.9 wt.% Fe–0.8% Zn alloy processed by spray forming was investigated. The alloy was gas atomized with argon and deposited onto a copper substrate. The microstructure was evaluated by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Small faceted dispersoids observed surrounding equiaxial α-Al matrix were identified by SEM–EDS as silicon particles. Sand cast samples with the same composition showed a columnar dendritic α-Al matrix, Al–Si eutectic, polyhedric α-AlFeSi and needle-like β-AlFeSi intermetallics. In the spray formed material the formation of the Al–Si eutetic was suppressed, and the formation of the α-AlFeSi and β-AlFeSi intermetallics was strongly reduced. The fine and homogeneous microstructure showed an aluminium matrix with grain size ranging from 30 to 40 μm, and particle size of the silicon dispersoids having a mean size of 12 μm. Room temperature tensile tests of the spray formed alloy showed relative increasing of strength and elongation when compared with the values observed for the conventionally cast counterparts. These results can be ascribed to the refined microstructure and the scarce presence of intermetallics of the spray formed material.

In the present work the fluxing technique was applied to the Sn–51 wt.% Se hypoeutectic alloy. The aim was to study the influence of the undercooling on the microstructure of this alloy, particularly concerning the formation of oriented microstructure and even some metastability occurrence. High undercooling (63 °C) was achieved for the primary SnSe phase leading to an oriented microstructure in the firstly solidified region. Although the undercooling for the eutectic was not so high (19 °C) morphological changes were observed. The rapid movement of the interface interfered with cooperative eutectic growth producing an irregular eutectic in the first region to solidify followed by a fine lamellar and directional eutectic. In order to detect some supersaturated solid solution in the SnSe phase a precise lattice parameter measurement was done from the accurate performed X-ray diffraction (XRD) on the firstly solidified region of the sample.

Understanding the crystallization of metallic glasses is essential for the consolidation of amorphous ribbons and powders into larger bodies. In this paper, we describe the evolution of crystalline phases formed during thermal induced crystallization of amorphous Al 84 Ni 8 Co 4 Y 3 Zr melt-spun ribbons. Partially and fully crystallized samples were prepared either by heating in a differential scanning calorimeter to temperatures corresponding to each crystallization stage or by isothermal annealing in a heated oil bath at 473 and 628 K (±1 K). Isothermal annealing time ranged from 1 to 120 min. Thermal analysis. X-ray diffraction and transmission electron microscopy were used to determine both the reactions involved and the phases formed upon crystallization. Crystallization occurred in multiple stages, with nanometer-sized crystals of fcc-Al and Al 9 Co 2 phases formed in the first and second initial stages, respectively, and formation of Al 16 Ni 3 Y-like. Al 3 Y and Al 3 Zr phases upon the final reactions. Both fcc-Al and Al 9 Co 2 were found to primarily crystallize from the amorphous material. An Al 16 Ni 3 Y-like phase was formed by polymorphous crystallization of the amorphous phase remaining after the second stage.

In the present work the Zr 55 Al 10 Ni 5 Cu 30 alloy has been processed by melt spinning and die-casting into a chilled copper mold. The ribbon was fully amorphous (X-ray diffraction and transmission electron microscopy) and cast samples partially crystalline. The amorphous ribbon was crystallized and analyzed by differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. The smaller supercooled liquid range of the glassy ribbons (60 K) and partial crystallization of a larger cast sample during quenching indicate the presence of oxygen in both samples (∼0.8 at.%). Although the crystallization process of the glassy ribbon, a glass transition followed by a single crystallization peak, showed the same crystallization process as reported by the literature, the heat release and the phases formed differed. The main phases formed were Zr 2 Cu, a complex `big-cube' fcc Zr 4 Cu 2 O-type phase and a tetragonal phase, not reported before to our knowledge, containing a lattice parameter of 2.8 nm.

Mg-based nanocrystalline alloys or nanocomposites are promising materials for hydrogen storage in the solid state, which is a more effective and safer storage medium than pressurized or liquefied hydrogen. Among the many Mg-based hydrides of interest for hydrogen storage, Mg2FeH6 is in a special position due to its relatively high gravimetric capacity of 5.5% and excellent volumetric density of 150 kg H2/m3. This work involved a study of the synthesis and processing of Mg-based alloys of this type, produced by high-energy ball milling and hot extrusion. A mixture of 2Mg-Fe was prepared by high-energy ball milling under argon gas. The resulting powder was cold-pressed to produce cylindrical pre-forms, which were then extruded and the sorption properties were analyzed in a microbalance and in a Sieverts apparatus. Phase formation, microstructural evolution, desorption temperatures, and hydrogen storage capacity were analyzed by X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry, and thermogravimetric techniques. The results showed that Mg2FeH 6 was formed and the hydrogen reaction was reversible. SEM observations indicate a microstructure composed of nanosized grains in the range of 30-80 nm inside particles of about 50 μm, and Mg2FeH 6 formed mainly at the particle interfaces. The desorption temperature started at about 225 °C, reaching a maximum at 440 °C with low capacity of absorption, indicating low absorption/desorption kinetics, probably due to bulk diffusion limitations. © 2010 Elsevier B.V.

Amorphous Fe‐M‐B (M‚Zr, Nb) based alloys with nanometer-sized crystallites have attracted attention due to their magnetic properties. Although corrosion resistance is a desirable property in such alloys, no study concerning this aspect has been reported. The eAect of metalloid content and partial crystallization on corrosion resistance of Fe‐M‐B (M‚Zr, Nb) amorphous alloys, Fe84Nb7B9 ,F e 84Zr7B9 and Fe83Zr3:5Nb3:5B9Cu1, was investigated. Corrosion resistance measurements were carried out by mass loss, potentiodynamic polarization, and thermogravimetric mass gain measurements. The partial crystallization of the amorphous alloy results in a decrease of the corrosion resistance for all the compositions analyzed. We also observed a greater corrosion resistance when Nb was present in comparison to the case when Zr was present. These results are an eAect of the superficial passive film protector formed. ” 2000 Published by Elsevier Science B.V. All rights reserved.

Process parameters optimization for the spray forming of a Cu–6% Zn alloy was developed by a combination of mathematical simulation and the factorial design method (FDM). The finite difference method was used for the mathematical simulation of the atomization stage and two levels FDM was applied considering the initial gas velocity, the axial distance between the atomizer and the substrate, the superheating of the melt and the melt flow rate. The validation of the optimized process parameters was done by processing the Cu–Zn alloy, a high-density deposit, as high as 98.5% of the theoretical density with a very homogeneous microstructure being produced.

Mechanical alloying, MA, is a high-energy ball milling technique, in which elemental blends are milled to achieve alloying at atomic level. This communication describes the results of an investigation on the phase transformation of a mixture of Fe and Si powders with 6wt%Si during MA processing. Besides the verification of the effect of milling time on the structure and on the compositional homogeneity, this study was undertaken in order to confirm, by using TEM technique, the possibility of amorphous phase formation for Si content lower than 17.7wt%.

Nano-quasicrystalline Al-Fe-Cr based alloys produced by rapid solidification processes exhibit high strength at elevated temperatures. Nevertheless, the quasicrystalline particles in these systems become unstable at high temperature limiting the industrial applications. In early works, it was observed that the use of Nb or Ta increases the stability of the Al-Fe-Cr quasicrystalline phase delaying the microstructural transformation to higher temperatures. Thus, these nano-quasicrystalline Al-based alloys have become promising new high strength material to be used at elevated temperatures in the automotive and aeronautical industries. In previous works, nano-quasicrystalline Al-Fe-Cr-Nb based alloys were obtained by rapid solidification using the melt-spinning technique. In order to obtain bulk alloys for industrial applications other fabrication routes such as powder production by gas atomization followed by compaction and extrusion are required. In the present work, the production of Al-Fe-Cr-Nb based alloys by powder atomization at laboratory scale was investigated. The powders obtained were sieved in different ranges of sizes and the microstructures were characterised by means of X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive of X-ray analysis. Mechanical properties have been measured by compression tests at room temperature and at 250C. It was observed that a very high temperature is required to produce these alloys by gas atomization; the icosahedral quasicrystalline phase can be retained after the atomization in powder sizes typically under 75um, and also after the extrusion at 375C. The extruded bars were able to retain a very high strength at elevated temperature, around 60% of the yield stress at room temperature, in contrast with the 10-30% typically obtained for many commercial Al alloys. Fil: Audebert, Fernando Enrique. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Grupo de Materiales Avanzados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentina Fil: Galano, Marina Lorena. University Of Oxford; Reino Unido Fil: Triveño Rios, C.. Universidade Federal Do Sao Carlos; Brasil Fil: Kasama, H.. Universidade Federal Do Sao Carlos; Brasil Fil: Peres, M.. Universidade Federal Do Sao Carlos; Brasil Fil: Kiminami, C.. Universidade Federal Do Sao Carlos; Brasil Fil: Botta, W. J.. Universidade Federal Do Sao Carlos; Brasil Fil: Bolfarini, C.. Universidade Federal Do Sao Carlos; Brasil

Ni-based bulk metallic glasses (BMGs) usually exhibit high thermal stability, excellent mechanical properties, and superior corrosion resistance. Glass forming ability (GFA), which determines the critical amorphous size, limits the application of Ni-based BMGs. In the present work, we studied the ternary Ni–Nb–Zr alloy system, which shows relatively high GFA and the presence of passive-film-forming elements Nb and Zr that are beneficial for corrosion resistance. The GFA of the Ni–Nb–Zr alloy system was evaluated by the topological instability, λ criterion, used to calculate the minimum topological instability maps which indicate the compositions where the topological instability reaches the maximum among the surrounding stable phases. Such criterion was also combined with the electronegativity difference among the elements (Δ e ) in each particular composition, which it is assumed to be related to the formation enthalpy (Δ H ) and glass stability of the corresponding alloy. The data from the literature for the maximum amorphous diameter were compared with the predictions of the topological λ criterion and with the combined criterion ( λ × Δ e ). Five compositions of rapidly solidified alloy ribbons were produced: Ni 45.5 Nb 23 Zr 31.5 , Ni 50 Nb 28 Zr 22 , Ni 57 Nb 17.5 Zr 25.5 , Ni 62 Nb 33 Zr 5, and Ni 79 Nb 8.5 Zr 12.5 . Structures of the samples were examined by X-ray diffraction (XRD). Glass transition, crystallization and melting behavior were investigated by a differential scanning calorimeter (DSC). The combined criterion ( λ × Δ e ) provided specific guidelines for locating high glass-forming alloys in the Ni–Nb–Zr alloy system.

The microstructure and the tensile properties of a spray-formed and extruded Al-9Si-4Cu-1Fe alloy were investigated. Manganese (0.3, 1, 2 in wt%) was added to the alloy to avoid the formation of the needle-like β-AlFeSi intermetallic phases that are highly detrimental to the alloy's ductility. The deposits were extruded at 623K with a n area reduction of 5 to 1. Small faceted dispersoids surrounding the equiaxial α-Al matrix, mainly in the form of silicon particles, were identified by SEM-EDS, as well as the Mn-containing α-Al15(Fe,Mn)3Si2 phase. The presence of the needle-like β-Al(Fe,Mn)Si was scanty, even with the lowest Mn content. The room temperature tensile tests of all the extruded alloys showed a significant increase in elongation to fracture when compared with the values observed fo r the as-spray formed deposits.This result can be ascribed to the elimination of porosity promoted by the extrusion process and to the smaller grain size of the extruded samples.