Aluminum Powder Mixtures Research Articles

Study on the Fabrication of Porous TiAl Alloy via Non-Aqueous Gel Casting of a TiH2 and Al Powder Mixture

A porous TiAl alloy with 23.78% porosity was successfully fabricated via a low-toxicity, non-aqueous gel casting method by using a titanium hydride (TiH2) and aluminum (Al) powder mixture as the raw material. The effects of dispersant content and solid loading on the rheological properties of the TiH2/Al slurries were studied systematically. It was found that all the slurries exhibited a typical shear-thinning behavior, which is favorable for the gel casting process. Three-point bending tests of the dried TiH2/Al green bodies were carried out, and the results showed that the flexural strength was raised from 28.86 to 62.36 MPa with increasing monomer (hydroxyethyl methacrylate, HEMA) content. In order to study the degreasing process and minimize the possible residual carbon and oxygen after sintering, TGA analysis was performed. The fracture morphology of the sintered TiAl alloy (1400 °C for 2 h) was studied by scanning electron microscope (SEM). Based on the X-ray diffraction (XRD) identification, the main phases of the sintered part were γ-TiAl, α2-Ti3Al, and a small amount of Al2Ti and Al3Ti.

Reaction pathway of NiAl/WC nanocomposite synthesized from mechanical activated Ni Al W C powder system

Abstract In this work, the mechanism of WC formation during mechanical alloying and subsequent annealing of nickel, aluminum, tungsten, and graphite powder mixtures was investigated. X-ray diffraction was used to evaluate phase changes. Microstructural and morphological evaluations of the powders were examined by FESEM and TEM. The XRD results confirmed that phase changes occurred by increasing milling time. After 10 h of ball milling, NiAl and W2C phases formed and new tungsten carbides were synthesized by increasing of milling time. After 40 h, W was consumed completely and WC, WC1-x, W2C carbides along with NiAl were produced. After heat treatment of 40 h milled powder, W2C and WC1-x phases disappeared and NiAl/WC nanocomposite was formed. The results confirmed that the WC formation was a gradual reaction controlled by atomic diffusion.

Rheological properties of alumina powder mixtures investigated using shear tests

The flow properties of alumina powder mixtures have been investigated using shear tests on a powder rheometer. The evolution of the flow index, ffc, as a function of the powder mixture composition show that all the points form a single curve whatever the pre-shear consolidation stress value adopted, the mixing conditions and the preconditioning of the powder bed (relative humidity) before the tests. It has been also shown that the flow properties of the mixtures are controlled by the competition between the inter-particle interaction forces (Van der Waals and capillary contributions) and gravity via the Bond number.

Microstructural Changes in Low-carbon Steel Occurring by Heating in Mixtures of Iron, Graphite and Alumina Powders

Microstructural Changes in Low-carbon Steel Occurring by Heating in Mixtures of Iron, Graphite and Alumina Powders

An investigation of SHS products in titanium, carbon (black carbon) and aluminum powder mixtures.

Metal matrix composite powders “TiC-Al binder” were synthesized in the wave combustion mode and investigated. Combustion concentration limits of Ti-Al-C powder mixtures were founded. Phase and elemental composition of self-propagating high temperature synthesis (SHS) products, morphology of composite powders and the dependence of the carbide phase size in the structure of the composite on the reaction mixture composition were investigated. The SHS composite powders have a lumpy, predominantly equiaxed shape, favourable for good flowability. The carbide inclusions size in the aluminium matrix decreases monotonically with a content increase of the of thermally inert aluminium binder.

Coating in the Ni-Al system using the SHS method

Using the method of self-propagating high-temperature synthesis, coatings based on aluminum nickelides were obtained. The processes occurring in the layers of a powder mixture of nickel and aluminum are studied. The influence of the coating thickness and the degree of dilution of the powder mixture with aluminum oxide on the maximum temperature of the combustion wave and the rate of its propagation is established. The coating consists of small crystals of NiAl, Ni3Al, fused together. The coating has good electrical conductivity and can be used as electric heaters.

The effect of Mg(NO3)2 addition on the formation of AlN nanowire by direct nitridation

In this study AlN nanowire was produced via direct nitridation (DN) method. In order to investigate the effect of nitridation on the formation of nanowire, elemental aluminum powder and ammonium chloride (NH4Cl) mixture was prepared with and without the addition of minor amount (0.5 wt%) of magnesium nitrate (Mg(NO3)2). The experiments were performed in a conventional electric resistance furnace coupled with a horizontal stainless-steel tube. Nitridation was carried out at 800–1000 °C for 2 h in N2 atmosphere. Differential scanning calorimetry and thermal gravimetric analyses were performed to powder mixtures, in order to examine the effect of Mg(NO3)2 addition on the morphology of AlN nanowire. X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM) and Energy-dispersive X-ray spectroscopy (EDS) techniques were also performed to identify to formed phases after the DN method. Using this technique, it was shown that with an addition of Mg(NO3)2 at 950 °C in N2 atmosphere a complete transformation to AlN nanowires was achieved having diameters of 40–45 nm.

Microstructure and Mechanical Behavior of Al-Mg Composites Synthesized by Reactive Sintering

Lightweight metal matrix composites are synthesized from elemental powder mixtures of aluminum and magnesium using pressure-assisted reactive sintering. The effect of the reaction between aluminum and magnesium on the microstructure and mechanical properties of the composites due to the formation of β-Al3Mg2 and γ-Al12Mg17 intermetallics is investigated. The formation of the intermetallic compounds progressively consumes aluminum and magnesium and induces strengthening of the composites: the yield and compressive strengths increase with the increase of the content of intermetallic reinforcement at the expense of the plastic deformation. The yield strength of the composites follows the iso-stress model when the data are plotted as a function of the intermetallic content.

Effect of Sintering Temperature and Heating Rate on Crystallite Size, Densification Behaviour and Mechanical Properties of Al-MWCNT Nanocomposite Consolidated via Spark Plasma Sintering

Powder mixture of ball-milled aluminium and functionalized multi-walled carbon nanotubes was compacted via spark plasma sintering (SPS) to study effects of sintering temperature and heating rate. An increase in sintering temperature led to an increase in crystallite size and density, whereas an increase in heating rate exerted the opposite effect. The crystallite size and relative density increased by 85.0% and 14.3%, respectively, upon increasing the sintering temperature from 400 to 600 °C, whereas increasing the heating rate from 25 to 100 °C/min led to respective reduction by 30.0% of crystallite size and 1.8% of relative density. The total punch displacement during SPS for the nanocomposite sintered at 600 °C (1.96 mm) was much higher than that of the sample sintered at 400 °C (1.02 mm) confirming positive impact of high sintering temperature on densification behaviour. The maximum improvement in mechanical properties was exhibited by the nanocomposite sintered at 600 °C at a heating rate of 50 °C/min displaying microhardness of 81 ± 3.6 VHN and elastic modulus of 89 ± 5.3 GPa. The nanocomposites consolidated at 400 °C and 100 °C/min, in spite of having relatively smaller crystallite size, exhibited poor mechanical properties indicating the detrimental effect of porosity on the mechanical properties.

Synthesis and characterization of the atomic laminate Mn2AlB2

Herein, we synthesize dense, predominantly single-phase polycrystalline samples of the Mn2AlB2 ternary compound, using reactive hot-pressing of manganese, aluminum, and boron powder mixtures under vacuum. With a Vickers hardness of 8.7 GPa, Mn2AlB2 is relatively soft for a transition metal boride and lacked dominant cracks at the corners of the indentations. With Young’s and shear moduli of 243 GPa and 102 GPa at 300 K, respectively, it is reasonably stiff. The Poisson’s ratio is calculated to be 0.19. With compressive strengths of 1.24 ± 0.1 GPa, the samples were quite strong considering the grain size (1–15 μm). The electrical resistivity at 300 K was ∼5 μΩm and decreased linearly upon cooling. At 0.0036 K−1, the temperature coefficient of resistivity was relatively high compared to MoAlB. The average linear thermal expansion coefficient was also found to be relatively high at 18.6 × 10-6 K−1 from 298 to 1173 K. Mn2AlB2 was not thermally stable above ∼1379 K. While Mn2AlB2 was not machinable with conventional tooling, intriguingly, high-speed carbide tools bits readily penetrate the surface – with no cracking or chipping for a few millimeters – before stopping.

Influence of compacting times and pressures on rheological properties of alumina and quartz ceramic powder mixtures

In this research the compacting and rheological properties of alumina and quartz powder mixtures were examined depending on forming pressures and times. On the basis of the achieved relative compaction curves as function of forming pressure and time the authors could successfully describe the changes of rheological behavior and rheological model of these powder mixtures. With increasing the compression pressure of the alumina and quartz powder mixtures considerable changes of rheological properties could be observed.In this work the authors have shown how the compacting deformations of cylindrical specimens are depending on compaction pressures and times. On the basis of their research the authors could successfully illustrate also how the rheological behaviors and models of alumina-quartz ceramic powder mixtures are changing in the compacting die cavities at low values of forming pressures.

Microwave Power Absorption Mechanism of Metallic Powders

Microwave processing of metallic powders, both in multimode and single-mode cavity, has attracted wide interest. However, the mechanism of interaction between microwaves and metal powders is not yet very well understood. In this paper, the microwave power absorption mechanism in metallic powders has been systematically studied. For this, mixtures of copper and alumina powders have been processed in a 2.45-GHz microwave single mode cavity in either air or forming gas (N2 + 5 wt% H2). In the nominal pure magnetic field (H-field) region in the single-mode microwave cavity, pure copper powder cannot be heated in the reductive (forming gas) atmosphere while it will heat in air atmosphere. Although neither alumina nor copper separately heat up in forming gas in the H-field, mixtures of copper and alumina powders heat up readily. These behaviors can be explained by the presence of oxide layers found on many metallic particles, which play a vital role in the microwave heating of metal powders. The oxide layers isolate the particles and confine the electric current to the surface of every particle, thereby allowing microwaves to penetrate into the sample. Since the particle size is quite small and the surface area is high, the heat produced by the sum of the surface currents on all of these particles is significant. Concurrently, the oxide layer on each metal particle may act as thermal insulation material to help maintain the temperature as the metal particles heat up since many metal oxides have low thermal conductivity. We propose a new mathematical model and derive the power dissipation equation which provides the fundamental basis for the analysis, calculation, and simulation of heating of metallic powders in microwaves.

Oxidation of Aluminum in Mixtures with Polyethylene after Plastic Deformation at High Pressures

Powder mixtures of low-density polyethylene and aluminum with the 20–80% weight ratio of the species are subjected to plastic deformation at pressures of 1 and 4 GPa in high-pressure devices of the Bridgman anvil type. Mass changes in the deformed mixtures in the temperature range from 30 to 800◦C are studied by the method of thermal gravimetry. A mass loss associated with polymer decomposition occurs in the temperature range from 30 to 450◦C, which is always smaller than the polymer content in the mixtures. A possible reason is the formation of thermally stable products due to aluminum interaction with polymer decomposition products. In the temperature range from 450 to 800◦C, the mass of the specimens increases, which is caused by aluminum oxidation and nitridation. The mass change depends on the deformation magnitude and pressure. To separate the oxidation and nitridation processes, the thermogravimetric measurements are performed in air, nitrogen, and argon. The thermal effects of aluminum interaction both with the polymer decomposition products and with oxygen and nitrogen are analyzed by the method of differential scanning calorimetry.

Effects of Sintering Temperature on the Mullite-Based Ceramics Fabricated from Rice Husk Ash

Mullite-based ceramics were prepared by utilizing agriculture by-product called as rice husk ash (RHA) from untreated rice husk (RH) and commercial alumina powdermixtures. Various samples were prepared accordingly with the mullite stoichiometric composition and subjected to the uniaxial hydraulic press. The green bodies, then were sintered to various temperatures at 1200 °C, 1300 °C, 1350 °C, 1400 °C, 1450 °C and 1500 °C in an electric furnace. Physical and microstructural characterization were done such as bulk density (BD), linear shrinkage (LS), X-ray fluorescence (XRF), X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). The sample M1, which composed the slightest RHA (40 %) was considered the optimum composition which produced the highest densification, 3.101 g/cm3 and the lowest linear shrinkage, 8.62 % which compareswith the theoretical mullite density. Besides, it is supported by the evidence of the presenceof mullite in the samples sintered 1300 °C (shown as elongated shape) as primary mullite and continued to grow at higher temperatures at 1400 °C (shown as equiaxed shape) as secondary mullite. The sintered samples showno evidence of mullite inearly at 1200 °C due to insufficient energy to diffuse for mullitization. As the sintering temperature increased, mullitization increased while decreasing the distribution of glassy phase and voids. The results revealed the high dependency of bulk density and linear shrinkage on the Al2O3 content and the values were gradually increased with the increase of sintering temperature. These findingsmay lead to the extended study ofthermal insulationmaterials as mullite ceramic is an excellent candidate for this application due to its properties.

Formation mechanism of high activity aluminide coating on Ni-CeO2 coated Rene 80 alloy

High temperature oxidation behavior of protective oxide scales can be improved by surface doping with reactive elements such as cerium. In this investigation, an intermediate Ni-CeO2 layer was electrodeposited on the surface of Rene 80 nickel-based superalloy before pack cementation aluminizing treatment. Electrodeposition of the Ni-CeO2 layer was carried out using direct current and Watts nickel electroplating bath containing 30g/lit nano ceria particles. Electrodeposited specimens were aluminized in a powder mixture of aluminum, ammonium chloride, and alumina by a two-step treatment at 760 and 1040°C to form an inward growth-type coating. Cross-sections of the coated specimens were studied by means of scanning electron microscopy, energy dispersive spectroscopy and X-ray diffractometry. The results showed that after aluminizing the composite intermediate layer converts to an Al-rich NiAl layer with a porous and CeO2-free surface zone below which a CeO2-containing layer exists. Three-zone microstructure of two-step aluminide coatings on nickel-based superalloys was observed below the CeO2-containing layer. The mechanism of coating formation was discussed. The oxidation resistance of the CeO2 modified coating in 10 five-hour cycles at 1050°C was considerably better than the unmodified coating.

Effects of foaming parameters on microstructure and compressive properties of aluminum foams produced by powder metallurgy method

Semi open-cell aluminum foams having channels between individual cells were produced using low cost CaCO3 foaming agent and applying the powder compact melting process. To this end, the aluminum and CaCO3 powder mixtures were cold compacted into dense cylindrical precursors for foaming at specific temperatures under air atmosphere. The effects of several parameters including precursor compaction pressure, foaming agent content as well as temperature and time of the foaming process on the cell microstructure, linear expansion, relative density and compressive properties were investigated. A uniform distribution of cells with sizes less than 100 μm, which form semi open-cell structures with relative densities in the range of 55.4%–84.4%, was obtained. The elevation of compaction pressure between 127–318 MPa and blowing agent up to 15% (mass fraction) led to an increase in the linear expansion, compressive strength and densification strain. By varying the foaming temperature from 800 to 1000 °C, all of the investigated parameters increased except compressive strength and relative density. The results indicated the optimal foaming temperature and time as 900 °C and 10–25 min, respectively.

Forming of Aluminum Foams by Deposition Process

In order to produce aluminum foams with designed density distribution, a deposition process of aluminum foam is examined. The precursor is made with the mixture of aluminum powder and a blowing agent, and it is heated, extruded with foaming and deposited onto the foam. In the density distribution of an aluminum foam bar made by the deposition process, high density area is found at the connection between the deposited foams. The combination of extrusion with foaming and without foaming makes clear variation of density within the deposited foam.

Oxidation Behavior and Mechanism of Al4SiC4 in MgO-C-Al4SiC4 System

Al4SiC4 powder with high purity was synthesized using the powder mixture of aluminum (Al), silicon (Si), and carbon (C) at 1800 °C in argon. Their oxidation behavior and mechanism in a MgO-C-Al4SiC4 system was investigated at 1400–1600 °C. XRD, SEM, and energy dispersive spectrometry (EDS) were adopted to analyze the microstructure and phase evolution. The results showed that the composition of oxidation products was closely related to the atom diffusion velocity and the compound oxide layer was generated on Al4SiC4 surface. In addition, the effect of different CO partial pressure on the oxidation of Al4SiC4 crystals was also studied by thermodynamic calculation. This work proves the great potential of Al4SiC4 in improving the MgO-C materials.

Hardness and Microstructure of Mixed Al-CNF Powder Extrusion

AbstractIn this study, mechanical properties and microstructures of extruded aluminum matrix composites were investigated. The composite materials were manufactured by two step methods: powder metallurgy (mixture of aluminum powder and carbon fiber using a turbular mixer, pressing of mixed aluminum powder and carbon fiber using a cold isostatic pressing) and hot extrusion of pressed aluminum powder and carbon fiber. For the mixing of Al powder and carbon fibers, aluminum powder was used as a powder with an average particle size of 30 micrometer and the addition of the carbon fibers was 50% of volume. In order to make mixing easier, it was mixed under an optimal condition of turbular mixer with a rotational speed of 60 rpm and time of 1800s. The process of the hot-extrusion was heated at 450°C for 1 hour. Then, it was hot-extruded with a condition of extrusion ratio of 19 and ram speed of 2 mm/s. The microstructural analysis of extruded aluminum matrix composites bars and semi-solid casted alloys were carried out with the optical microscope, scanning electron microscope and X-ray diffraction. Its mechanical properties were evaluated by Vickers hardness and tensile test.

Terahertz acoustic phonon detection from a compact surface layer of spherical nanoparticles powder mixture of aluminum, alumina and multi-walled carbon nanotube

We present terahertz spectroscopy study on spherical nanoparticles powder mixture of aluminum, alumina, and MWCNTs induced by surface mechanical attrition treatment (SMAT) of aluminum substrates. Surface alloying of AL, Al2O3 0.95% and MWCNTs 0.05% powder mixture was produced during SMAT process, where a compact surface layer of about 200 μm due to ball bombardment was produced from the mixture. Al2O3 alumina powder played a significant role in MWCNTs distribution on surface, those were held in deformation surface cites of micro-cavities due to SMAT process of Al. The benefits are the effects on resulted optical properties of the surface studied at the terahertz frequency range due to electrical isolation confinement effects and electronic resonance disturbances exerted on Al electronic resonance at the same range of frequencies. THz acoustic phonon around 0.53–0.6THz (17–20cm−1) were observed at ambient conditions for the spherical nanoparticles powder mixture of Al, Al2O3 and MWCNTs. These results suggested that the presence of Al2O3 and MWCNTs during SMAT process leads to the optically detection of such acoustic phonon in the THz frequency range.