Intermetallic Materials Research Articles

A front tracking model of the MAXUS-8 microgravity solidification experiment on a Ti-45.5at.% Al-8at.%Nb alloy

On 26th March 2010 the MAXUS-8 sounding rocket was launched from the Esrange Space Center in Sweden. As part of the Intermetallic Materials Processing in Relation to Earth and Space Solidification (IMPRESS) project, a solidification experiment was conducted on a Ti-45.5at.%Al-8at.%Nb intermetallic alloy in a module on this rocket. The experiment was designed to investigate columnar and equiaxed microstructures in the alloy. A furnace model of the MAXUS 8 experiment with a Front Tracking Model of solidification has been developed to determine the macrostructure and thermal history of the samples in the experiment. This paper gives details of results of the front tracking model applied to the MAXUS 8 microgravity experiment. A model for columnar growth is presented and compared to experimental results for furnace A of the experiment module.

Microstructure and Superconductive Property of MgB<sub>2</sub>/Al Composite Materials

MgB2 has the higher critical temperature of superconducting transition (TC : 39K) among the intermetallic compound superconductive materials, however, MgB2 is hard for practical use because of its unworkable and lower critical current density (JC) in a high magnetic field than Nb-based superconductive materials. We have developed the original method of three-dimensional penetration casting (3DPC) to fabricate the MgB2/Al composite materials. In the composite material we made, MgB2 particles dispersed to the matrix uniformly. Thus, these composite materials can be processed by machining, extrusion and rolling. The TC was determined by electrical resistivity and magnetization to be about 37～39K. In this work, we made composite material with ground MgB2 particle with the purpose of extruding thinner wires of composite material, successfully produced φ1mm wire and changed the matrix from pure Al to Al-In alloy. JC of composite materials with the matrix of Al-In alloy was calculated from the width of the magnetic hysteresis based on the extended Bean model. The result was better than that of MgB2/Al composite material without Indium. Microstructures of these samples had been confirmed by SEM observation.

Superior (de)hydrogenation properties of Mg–Ti–Pd trilayer films at room temperature

In this paper, a series of Mg-Ti-Pd trilayer films with various thicknesses of the Ti interlayer were prepared by magnetron sputtering. The trilayer films could be reversibly (de)hydrogenated at room temperature. The relationship between structure and properties of Mg-Ti-Pd trilayer films was comprehensively investigated. Our studies showed that the hydrogen storage properties of Mg-Pd films were significantly improved with the addition of a Ti interlayer. The optimal hydrogenation properties were obtained when the Ti interlayer was 1 nm. The superior hydrogenation properties achieved by introduction of the Ti interlayer could be attributed to several aspects: prevention of Mg-Pd alloying; catalytic dissociation of H(2) molecules and provision of heterogeneous nucleation sites. These results were elucidative for the development of high performance intermetallic hydrogen storage materials and thin film based functional devices.

Challenges in intermetallics: synthesis, structural characterization, and transitions

Intermetallics that contain rare-earth elements are particularly interesting because of their temperature- and pressure-dependent structural and physical transitions that make them potential candidates for magnetic applications. This article highlights synthetic routes and structural characterization advancements used to investigate intermetallic materials. Experimental and theoretical examples of three intermetallic structure types--ThCr(2)Si(2), Heusler and Laves--are discussed to present a historical review and to illustrate the grand challenges in unravelling structure-property relationships of intermetallic compounds.

Microstructure and Superconductive Property of MgB2/Al Composite Materials

MgB2has the higher critical temperature of superconducting transition (TC: 39K) among the intermetallic compound superconductive materials, however, MgB2is hard for practical use because of its unworkable and lower critical current density (JC) in a high magnetic field than Nb-based superconductive materials. We have developed the original method of three-dimensional penetration casting (3DPC) to fabricate the MgB2/Al composite materials. In the composite material we made, MgB2particles dispersed to the matrix uniformly. Thus, these composite materials can be processed by machining, extrusion and rolling. TheTCwas determined by electrical resistivity and magnetization to be about 37～39K. In this work, we made composite material with ground MgB2particle with the purpose of extruding thinner wires of composite material, successfully produced φ1mm wire and changed the matrix from pure Al to Al-In alloy.JCof composite materials with the matrix of Al-In alloy was calculated from the width of the magnetic hysteresis based on the extended Bean model. The result was better than that of MgB2/Al composite material without Indium. Microstructures of these samples had been confirmed by SEM observation.

Giant magnetostriction in magnetite nanoparticles

Typically the value of the magnetostrictive coefficient (λ) observed for bulk magnetic materials such as cubic ferrites is 10−6. However, giant magnetostriction (λ ≤ 10−3) is only observed in a few bulk intermetallic materials based on alloys of rare earth and iron such as TbFe, TbFe2, DyFe2 and Terefenol-D. While giant magnetostriction is known in nanostructured films, we show for the first time, this phenomenon occurs in magnetic nanoparticles. By using in-field small angle X-ray scattering (SAXS) as a tool, we demonstrate that a 4% relative change in dimension of the particle can be observed in 5.0 nm Fe3O4 nanoparticles at room temperature with 1 kG magnetic field. Also, we propose that the observed values are due to interaction effects and magnetoelastic coupling of particle magnetic moments and external magnetic field.

The corrosion behavior of porous Ni3Al intermetallic materials in strong alkali solution

Porous Ni3Al alloys was prepared by cold pressing and reactive synthesis of Ni and Al elemental powders via the Kirkendall effect. Corrosion behavior of porous Ni3Al alloys was investigated by electrochemical tests and weight change measurements. Polarization resistance indicated that porous Ni3Al had more positive free corrosion potential and lower corrosion current than porous Ni and porous Ti and exhibited a wider passive region. The immersion test revealed that after 2000 h immersion, the weight change and pore structure of porous Ni3Al stayed stable in KOH solution. The influence of temperature on corrosion behavior and corrosion mechanism of porous Ni3Al were also discussed.

Experimental Study of Thermal and Flame Front Characteristics in Combustion Synthesis of Porous Ni-Ti Intermetallic Material

This article describes experimental investigation of thermal and combustion phenomena during the self-propagating combustion synthesis of Ni-Ti intermetallic materials for structural application. Ni-Ti mixture is prepared from elemental powders of Ni and Ti. The mixture is pressed into solid cylindrical samples of 1.1-cm diameter and 2-3-cm length, with initial porosity ranging from 30 to 42%. The samples are preheated to various initial temperatures and ignited from the top surface such that the flame propagates axially downward. The flame speed images are recorded with a motion camera, and the temperature profile is recorded. The flame front propagation velocity is deduced as a function of the preheat temperature and initial porosity as well as the effective thermal conductivity of the reactants.

Microstructure of Directionally Solidified Ni-Ni<sub>3</sub>Si Hypoeutectic <i>In Situ</i> Composite

Ni3Si compound is one of the excellent high temperature structural materials, because it possesses the attributes of high melting point, high strength, low density, excellent oxidation resistance at elevated temperatures, and magnificent corrosion resistance in acid environments, particularly sulfuric acid solutions, while the application of this compound is limited due to poor ductility at ambient temperatures and lack of fabricability at high temperatures. The incorporation of a ductile phase into the intermetallic materials has become an attractive means to modify the ductility. In this paper Ni-Ni3Si hypoeutectic in situ composites are obtained by Bridgman directional solidification technology. Microstructure of the Ni- Ni3Si hypoeutectic in situ composites are regular lamellar eutectic structure at the lower solidification rates, whereas eutectic cells or dendrites can be found with the increase of the solidification rate, due to the increase of the composition undercooling. Moreover, the directional solidification mechanism was investigated as well.

Simple rules for the understanding of Heusler compounds

Abstract Heusler compounds are a remarkable class of intermetallic materials with 1:1:1 (often called Half-Heusler) or 2:1:1 composition comprising more than 1500 members. Today, more than a century after their discovery by Fritz Heusler, they are still a field of active research. New properties and potential fields of applications emerge constantly; the prediction of topological insulators is the most recent example. Surprisingly, the properties of many Heusler compounds can easily be predicted by the valence electron count. Their extremely flexible electronic structure offers a toolbox which allows the realization of demanded but apparently contradictory functionalities within one ternary compound. Devices based on multifunctional properties, i.e. the combination of two or more functions such as superconductivity and topological edge states will revolutionize technological applications. The subgroup of more than 250 semiconductors is of high relevance for the development of novel materials for energy technologies. Their band gaps can readily be tuned from zero to ≈4 eV by changing the chemical composition. Thus, great interest has been attracted in the fields of thermoelectrics and solar cell research. The wide range of their multifunctional properties is also reflected in extraordinary magneto-optical, magnetoelectronic, and magnetocaloric properties. The most prominent example is the combination of magnetism and exceptional transport properties in spintronic devices. To take advantage of the extremely high potential of Heusler compounds simple rules for the understanding of the structure, the electronic structure and the relation to the properties are reviewed.

Variable temperature performance of intermetallic lithium-ion battery anode materials

Although a variety of cathode and electrolyte materials have been studied and commercialized over the past two decades, nearly all commercial cells have used a graphitic carbon anode. Several reasons exist for this choice—including cost, low insertion voltage, and ease of use in the cell manufacturing process. However as uses for lithium-ion batteries expand, alternative anodes that may offer better energy and power capability are being explored. For transportation-oriented purposes, anodes based on simple lithiated Zintl compounds, e.g. Li 17Sn 4, or intermetallic insertion anodes offer significant advantages in capacity (volumetric and gravimetric) and stability in the cell environment that make them attractive candidates for future cell chemistries. Within this context, little however is known about how these alternative anode materials perform as a function of temperature, which is important for applications where operation at temperatures as low as −30 °C can be expected. In this study we evaluated a series of intermetallic insertion anodes that operate by a simple metal displacement mechanism. We have found that for Cu 6Sn 5, Ag/Cu 6Sn 5, and Cu 2Sb, the drop-off in performance with temperature is in line with that observed for a commercial graphite-based anode and indicates that additional variables such as cation diffusion through the electrode passivation film or the electrochemical double layer may be playing an important role that is independent of the underlying anode material. We additionally characterized the NiAs-type mineral Sorosite (CuSn 0.9Sb 0.1), as various literature reports had indicated that substitution of antimony for tin eliminated the need for interstitial copper, however powder X-ray diffraction studies of samples made by annealing or high energy ball milling indicated mixed phase samples.

Bimetallic nanoparticles of copper and indium by borohydride reduction

This study investigated the preparation of copper–indium bimetallic nanoparticles through the borohydride reduction in an alcohol solution for application in ink-coating and sputtering target materials. Copper, indium metal and copper–indium intermetallic materials were synthesized by reacting CuCl 2 and InCl 3 with NaBH 4 in 2-propanol (IPA) and tetraethylene glycol (TEG) at room temperature. The Cu–In samples contained Cu 2In and CuIn phases with particle sizes of 10–100 nm and 30–200 nm in both the IPA and TEG solutions, respectively. The nanoparticulate Cu–In precursor layer was coated onto a soda-lime glass through spin-casting, where the Cu–In intermetallic phases of Cu 2In and Cu 11In 9 were produced through heat treatment in Ar gas and a microstructured CuInSe 2 layer was produced in a selenium atmosphere. Cu, In, Cu–In intermetallic nanoparticles and the films were characterized using powder X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray analyses.

Tribological evaluation on Ni3Al-based alloy and its composites under unlubricated wear condition

Friction coefficients and specific wear rates of an existed Ni3Al-based NAC-alloy with composition of Ni-18.8Al-10.7Fe-0.5Mn-0.5Ti-0.2B (at.%) and its composites reinforced by 6 vol.% Cr3C2- and 6 vol.% MnS-particles, respectively were investigated for the initial understanding of sliding wear behaviors of the materials under unlubricated condition. The testing materials were prepared by hot isostatic pressing (HIP) process. Pin-on-Disk (POD) measurements were carried out under room temperature condition. A commercial vermicular graphite cast iron was selected as a reference material. The disks used in this study were made of a grey cast iron as cylinder liner materials of ship engines. The contact pressure of 2.83 MPa and 5.66 MPa were applied in POD tests. The experimental results revealed that the monolithic NAC- alloy has the almost same values of friction coefficient and specific wear rate under the testing condition as compared to a commercial vermicular cast iron. The wear mechanism is probably conducted to its intrinsic deformation mechanism of the Ni3Al-type of intermetallics. For the composite with 6 vol.% hard Cr3C2-particle, wear rate was reduced on both sides of pin and disk up to 50%, comparing to the single phase NAC-alloy at a high load of 5.66 MPa. By an addition of 6 vol.% soft MnS-particle, wear rate of the disk was dramatically decreased and friction coefficient also slightly reduced on the test. But, the wear rate of pin is maintaining as the same level as the monolithic NAC-alloy and the reference vermicular cast iron. The present investigation recognized that it will be potential to develop Ni3Al-matrix composites reinforced by hard Cr3C2- and/or soft MnS-particles for a certain tribological applications, especially other excellent physical, chemical and mechanical properties of the Ni3Al-based intermetallic materials were considered.

Synthesis and characterisation of the compound CoSbS

In the search for new intermetallic materials with high thermoelectric performances, the Co–Sb–S ternary system has been explored and polycrystalline CoSbS samples have been prepared by a vapour phase technique starting from the pure elements. The crystal cell of CoSbS belongs to the Pbca space group and shows an orthorhombic structural arrangement with the following lattice parameters: a = 5.8341(2) A; b = 5.9477(2) A, and c = 11.6540(4) A. The structure belongs to the pyrite–marcasite family, as Co forms tilted corner- and edge-sharing octahedra with three Sb and three S atoms. Scanning electronic microscopy (SEM), electron-probe microanalysis (EPMA) and X-ray powder diffraction were used to investigate the microstructure and to carry out the structural analysis; the crystal structure was refined by the Rietveld method using the DBWS-9807 program. The thermal stability of CoSbS was investigated referring to the ternary Co–S–Sb phase diagram and by differential thermal analysis (DTA) measurements. Thermoelectric power measurements at room temperature were also performed by a home-made instrument.

Superconductive Property and Microstructure of MgB<sub>2</sub> Particle-Dispersed Aluminum Based Composite Materials

Superconducting wires have been applied for the fabrication of superconducting magnets in nuclear magneto-resonance (NMR), Magneto-resonance imaging (MRI) and so on. MgB2 has the highest critical temperature of superconducting transition (TC39K) among intermetallic compound superconductive materials. This means that MgB2 Superconductive wire doesn’t need expensive liquid He for cooling. We used the original method of the three-dimensional penetration casting (3DPC) in this laboratory to fabricate the MgB2/Al composite. Our 3DPC method for fabricating composite materials can disperse particles in the matrix homogenously without any aggregation and control volume fractions of composites within the range of 4 – 40%, even when particle size is less than 1 m. Thus, these composite materials can be processed by machining, extrusion and rolling. In the composite material we made, MgB2 particles dispersed to the Al matrix uniformly. The TC was determined by electrical resistivity and magnetization to be about 37 – 39K. We succeeded in extruding MgB2/Al composite billet to 1mm wire. Microstructures of these samples have been confirmed by SEM method. MgB2/Al composite billet and extruded wire were showed there no cracks inside the materials.

The Development of a Microgravity Experiment Involving Columnar to Equiaxed Transition for Solidification of a Ti-Al Based Alloy

The authors are members of the integrated project Intermetallic Materials Processing in Relation to Earth and Space Solidification (IMPRESS), funded within the European Framework (FP6). One of the aims of IMPRESS is to develop new alloys and processes for the casting of TiAl-based turbine blades for the next generation of aero and industrial gas turbine engines. Within IMPRESS, two related issues have been identified during the primary solidification stage, namely, segregation and the columnar-to-equiaxed transition (CET). The authors have set out to isolate the effects of thermo-solutal convection, by designing a microgravity experiment to be performed on a European Space Agency platform. This experiment will investigate the CET formation during solidification. It is planned to use a sounding rocket providing a microgravity time of approximately twelve minutes. The results of this microgravity solidification experiment will be used as unique benchmark data for development and validation of new computational models of TiAl solidification. This in turn will produce accurate models and ultimately new robust industrial processes by project partners in the aerospace industry. The evolution of the design of the microgravity experiment is discussed and the results of preliminary ground reference experiments are presented. Future plans and objectives for the project are also highlighted.

Numerical Simulation of TiAl-Nb Alloy Solidification Experiment in TEM 01-3M Facility Aboard MAXUS 8

The problem of numerical modeling of directional solidification of TiAl refractory intermetallics aboard the MAXUS 8 sounding rocket is considered. The research is of relevance to the FP6 Integrated project IMPRESS (Intermetallic Materials Processing in Relation to Earth and Space Solidification). Attention is paid to columnar-to-equiaxed microstructure transition (CET) phenomenon and mushy zone evolution in Ti-45.9Al-8Nb (at %) alloy being processed in TEM 01-3M high-temperature (up to 17000C) furnace. In this three-zone resistive furnace the “bent” temperature profile is applied with two strongly different axial thermal gradients, presumably allowing the achieving of CET conditions along the sample of 160 mm length. Temperature profile evolution is defined by power-down furnace operation. 2D-numerical study of heat transfer and realtime-scale solidification dynamics of TiAl-Nb under zero gravity approximation is performed. The approaches used for solution of Navier-Stokes equations and phase transition (Stefan) problem are briefly described. The solidification time is shown to be satisfying the 12-minute microgravity limit aboard a MAXUS. The position and the time at which CET may be triggered are predicted and confirmed in line with the Hunt diagram. The comparison is performed of model predictions with the real microstructure of TiAl-Nb reference sample solidified on-ground in TEM 01-3M facility.

High-temperature relaxation analysis in a fine-grain B2 FeAl intermetallic

The study of anelastic relaxation by means of mechanical spectroscopy gives a unique insight into the mechanisms of defect mobility, and provides crucial information for the development of new intermetallic materials. In this work, a new high-temperature mechanical spectrometer, working up to 1800 K, is used to perform such study in order to better understand the underlying processes controlling plasticity in an advanced Fe-38% Al intermetallic. The measured internal friction spectra, as a function of temperature for different frequencies, show one internal friction peak at about 1100 K with a background increasing exponentially with temperature up to 1350 K. In this work we apply a model that gives a consistent description of the high-temperature internal friction background in order to obtain the parameters characterizing the involved relaxation processes: H act = 5.4 ± 0.2 eV and τ 0 = 1.4 × 10 −19 s. This apparent activation energy of the high-temperature background is compared with results in the literature obtained by creep tests and discussed in terms of the possible microscopic mechanisms. Moreover, the subtraction of the obtained background allowed a more precise measure of the activation enthalpy for the 1100 K relaxation peak: H peak = 2.98 ± 0.02 eV. We conclude that the mechanisms operating in this temperature range should be related to those controlling creep in these materials.

Síntesis coloidal de materiales nanoestructurados de Al-ZrAl<sub>3</sub>: Propiedades mecánicas mediante el ensayo miniatura de punzonado

This work describes a new method to obtain Al-Zr intermetallic nanostructured materials by using a colloidal processing technique. The combination of Al powders and zirconium IV-propoxide (C12H28O4Zr) under controlled conditions results in a metal matrix composite with a homogeneous dispersion of intermetallics. Synthesis was carried out in a tubular furnace under argon and by hot pressing under the same atmospheric conditions. XDR and SEM were used to identify the intermetallic nanoparticles. The Vickers hardness of the ZrAl3 nanocomposites and the mechanical behaviour by small punch test were studied.

First and second order quantum phase transitions in multi-band superconductors

Abstract In multi-band and inter-metallic materials superconductivity can be destroyed by applying external pressure in these systems. In many cases the critical temperature is driven continuously to zero, the superconducting to normal transition being associated with a superconducting quantum critical point (SQCP). In this paper we propose a model for this type of SQCP based on the increase of hybridization as pressure is applied in the material. We study a two-band superconductor with hybridization V between these bands. We use a BCS approximation and include both inter- and intra-band attractive interactions. We show that for negligible inter-band interactions, as hybridization increases there is a second order phase transition from a superconductor to a normal state at zero temperature at a critical value of the hybridization V c . This SQCP can be reached by pressure, since this external parameter controls hybridization in the system. We also find discontinuous transitions at zero temperature and the appearance of a gapless superconducting (GS) phase in a certain range of hybridization in the case of inter-band interactions being dominant.