Pure Aluminum Powder Research Articles

Production of Al–Al3Ti powders by mechanical alloying and annealing

Mixed powders of Al and Ti (10 wt-%) have been mechanically alloyed in an attritor mill under vacuum or nitrogen atmosphere. Pure aluminium powders have also been prepared, in the same conditions, for comparison. After milling for 10 h, a metastable solution of Ti in an Al matrix is obtained, with ∼9 wt-%Ti dissolved in the matrix. The evolution of these powders during milling is reported. Their thermal stability has been studied using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), identifying the observed changes by X-ray diffraction (XRD). Annealing of these powders at different temperatures, up to a maximum of 625°C, produces the precipitation of new phases, such as Al4C3 and different structures of Al3Ti, as well as grain growth. The appearance of these second phases, and their influence on powder microhardness, has been characterised as a function of the selected heat treatment temperature.

Deposition of Sn-Al Onto Aluminum Powder in Its Self-Convective Motion by DC Sputtering

The deposition of Sn-5wt.%Al alloy onto pure aluminum powder in its self-convective motion by magnetron DC sputtering was examined in order to prepare Al-Sn composite particles, aiming not only at the development of highly uniform sintered binary compact materials but also at the improvement of the bonding between the aluminum particles after sintering at low temperature such as 250°C. The self-convection phenomenon of the aluminum powder in the vacuum chamber occurred when a perpendicular vibration was applied to the powder. The sputter-deposition of the Sn-Al alloy was carried out during the self-convection of the aluminum powder. Under SEM and according to EPMA analysis, as well as according to thermal analysis with DSC, it was confirmed that the obtained particles were coated with the Sn-Al deposits. Therefore it was found that Sn-Al composite powder could be produced by this processing, and thereby not only the development of highly uniform sintered binary compact materials but also the improvement of the bonding between the aluminum particles after sintering at low temperature were expected.

Pyrolytic and graphitic carbon: pressure induced phases segregated in polycrystalline corundum

Two different carbon phases have been identified in a lab-synthesised pure alumina powder after hot press sintering at 1500 °C and 50 N inside graphite moulds. The chemical analysis reveals important amounts of carbon as the impurity introduced during densification. Furthermore, HRTEM and EFTEM carbon maps demonstrate the presence of carbon at grain boundaries and triple points of the alumina matrix. Electron diffraction and ELNES spectra confirm the existence of pyrolytic carbon on triple points, with an approximate d-spacing of 0.34 nm, while at the alumina grain boundaries it transforms into crystalline graphene slabs. Oxidized samples at 1500 °C over 10 hours gave almost C-free white alumina samples.

FEASIBILITY OF Al/Al2O3 COMPOSITE PARTICLES PREPARED BY SEMI-SOLID MECHANICAL STIRRING METHOD

A discrete coating of aluminum particles on the surface of Al 2 O 3 particles was prepared by the semi-solid mechanical stirring method. Al 2 O 3 particles with an average diameter of 80 μm, preheated to about 300°C, were added to semi-solid pure aluminum to prepare a slurry by the mechanical stirring method. The volume fraction of Al 2 O 3 particles in the slurry was about 20%. As the ceramic particles were uniformly dispersed in the semi-solid aluminum, the temperature of the slurry decreased quickly, but the slurry continued to be stirred until all the slurry was converted into composite powder. The composite powder was then cooled down to room temperature in a steel block cooler in an argon atmosphere. The surface morphology and transverse sections of the composite powder were examined using a scanning electron microscope (SEM), electron probe X-ray microanalyser (EPMA), optical microscope and augur electron spectroscopy (AES). The results indicate that the composite powder was a mixture of Al/Al 2 O 3composite particles and pure aluminum powder in quasi-spherical shapes. A single layer of nano-, submicron- and micron-sized aluminum particles were coated on the surfaces of the Al 2 O 3 particles. The slurry could be converted into the composite powder resulting from faster solidification of liquid aluminum and mechanical stirring.

Some aspects of workability studies in cold forging of pure aluminium powder metallurgy compacts

Powder metallurgy is a rapidly developing manufacturing process for the production of precision components in industries. This technique involves compaction, sintering and plastic deformation (forging). In this paper, a detailed discussion on a workability factor of aluminium powder metallurgy compacts with respect to the combined effect of the mean stress and the effective stress is described and compared for the cases of uniaxial upsetting, plane stress upsetting and triaxial stress state of upsetting.

DC resistivity of alumina and zirconia sintered with TiC

Pure alumina and zirconia powders were sintered separately with increasing amount of TiC up to ∼ 65 vol.%, as a conducting second phase with an aim to prepare conducting structural ceramics which can be precisely machined by EDM technique. TiC did not help in sintering the parent phase but it decreased the d.c. resistivity of the composite to 1 ohm.cm at ∼ 30 vol.% loading. The conductivity is explained by the effective media and percolation theories.

Lanthanide Diffusion in Single Crystalline and Polycrystalline Pure or Yttrium Doped Alpha-Alumina

In order to bring a contribution to cationic diffusion in alpha-alumina, results on diffusion of 14 lanthanides and Y are presented. Samples are either single crystals with a known orientation or polycrystals with various grain-sizes elaborated from Y-doped alumina powders (100 ppm or 1000 ppm) or from pure alumina powder. After pre-heating in air at the diffusion temperature, small drops of a solution containing these elements are deposited at the surface of the sample. After the diffusion treatment (1200°C, 48 h or 1300°C, 21h), the diffusion profiles are obtained by a CAMECA IMS 4F SIMS device. The isotopes which are taken in account are: 45Sc, 89Y, 139La, 140Ce, 141Pr, 146Nd, 147Sm, 153Eu, 158Gd, 159Tb, 163Dy, 165Ho, 166Er, 169Tm, 174Yb and 175Lu which are the most suitable for this analysis. At first, it can be observed that the diffusion profiles are quite the same for all lanthanides. Diffusion profiles obtained for single crystals allow to calculate the lattice diffusion coefficients, which are necessary to determine the diffusion coefficients values in grain boundaries. Lattice and grain-boundary diffusion coefficients values are compared with cationic diffusion coefficients determined earlier.

多孔質アルミニウム焼結体の特性に及ぼす原料粒径の影響

In the powder metallurgical process, porous aluminium compacts were prepared by using pure aluminium powders and resin particles as the raw materials. The resin powders classified at more than 250 μm, 110∼250 μm, and less than 110 μm mixed with pure-aluminium powder having average particle size of 20 μm, 10 μm, and 3 μm at the content of 56 vol.%. This mixtures were press-molded into column shape (d=11 mm, L=16∼17 mm). To form pores, resin particles in the green compacts were removed by heat-treatment at 380°C in Ar-gas flow, and then the compacts were sintered at 655°C for 2 hours in vacuum. Effects of particle size of raw materials on the densities and static compressive properties at room temperature for sintered compacts were mainly investigated. The relative densities of sintered compacts were within the range of 39%∼47% on the above-mentioned process conditions. Reduction in particle size of either aluminiun powder or resin particle resulted in higher density. The compressive strength increased with dcreasing the size of aluminium powder. When aluminium powder was 10 μm and 3 μm, the compressive strength increased with decreasing size of resin particle. Especially, the sintered compacts originating in resin particle less than 110 μm had much higher strength than the others regardless of size for aluminium powder.

合金元素を混合したアルミニウム粉末を用いるレーザ積層造形

In this paper, the three dimensional laser fabrication of aluminum alloy is investigated. While the processed bead of pure aluminum powders by laser irradiation is ordinarily discontinuous in the shape of balls and is not welded to the base plate, the continuous bead suitable for a fabrication unit can be processed using aluminum powders compounded with alloy elements. A smooth bead with deviation of the maximum height of less than 0.1mm is obtained on the titanium base plate under the optimum processing conditions. The bead of the aluminum powders compounded with 5-7.5wt% the silicon and 5wt% the titanium can be laminated to the plate of smooth top without cracks or detachment from the base plate by the change of melting and solidifying process. In this processed bead the eutectic microstructures are observed containing aluminum-silicon alloy and Al3Ti distributed minutely with the grain size under 20 micrometer. The average tensile strength of this processed plate is equivalent to pure aluminum at 82 MPa. Three dimensional shapes of aluminum alloy, for example quadrangular pyramids, are fabricated easily with smooth appearance of the surface.

Nitrogen pressure effects on non-isothermal alumina sintering

The densification of a fine grained pure alumina powder was studied during gas pressure sintering. Different nitrogen pressures were applied during non-isothermal sintering runs up to final temperatures between 1150 °C and 1650 °C. Densification, porosity and microstructures have been investigated. A fine alumina powder presents a densification delay during nitrogen pressure sintering mainly due to the gas pressure effect at the beginning of the sintering. The main results of this work concern the influence of nitrogen pressure on non-densifying mechanisms and microstructural evolution, which only depends on densification rate.

Nanometer, submicron and micron sized aluminum powder prepared by semi-solid mechanical stirring method with addition of ceramic particles

Abstract Composite powder, which is a mixture of Al/Al 2 O 3 composite particles and nanometer, submicron and micron sized aluminum powder, was prepared by semi-solid mechanical stirring method with addition of Al 2 O 3 ceramic particles. The ceramic particles have an average diameter of 80 μm and a volume fraction of 15% in the slurry. The methods used to measure the size distribution of particles greater than 50 μm and less than 50 μm were sieve analysis and photosedimentation, respectively. The surface morphology and transverse sections of the composite powder of different sizes were examined by scanning electron microscope (SEM), optical microscope and auger electron spectroscopy (AES). The results indicate that the composite powder prepared in present work have a wide size distribution ranging from less than 50–900 μm, and the aluminum particles and Al/Al 2 O 3 composite particles are separated and isolated. The particles greater than 200 μm and less than 50 μm are almost pure aluminum powder. The rate of conversion of ingot aluminum into particles less than 1 μm containing nanometer and submicron sizes is 1.777 wt.% in this work. The aluminum powder of different sizes has different shape and surface morphology, quasi-spherical in shape with rough surface for aluminum particles of micron scale, irregular in shape for aluminum particles of submicron scale, and quite close to a globular or an excellent globular in shape for aluminum particles of nanometer size. On the other hand, the surface of ceramic particle was coated by aluminum particles with maximum thickness less than 10 μm containing nanometer and submicron sizes as a single layer. It is suggested that the surface of ceramic particles can provide more nucleation sites for solidification of liquid aluminum and the nucleation of liquid aluminum can take place readily, grow and adhere on the surface of ceramic particles, although it is poorly wetted by the liquid aluminum and the semi-solid slurry can convert into composite powder owing to the addition of ceramic particles and the shear force of mechanical stirring during solidification.

Laminar Lifted Flame Speed Measurements for Aerosols of Metals and Mechanical Alloys

This research develops and validates a novel experimental methodology for measurements of laminar flame speed of metal-air aerosols. The methodology is based on a recently developed laminar, lifted flame aerosol burner (LLFAB) using electrostatic fluidization to produce metal aerosol between the electrodes of a plate capacitor. An aerosol jet directed vertically up, and decelerating in a stagnant gas environment is produced. The jet is ignited, and the position of the propagating downward flame is stabilized at a location where the flame speed becomes equal to the jet velocity with the opposite sign. Therefore, the flame speed determines the vertical location of the lifted flame. Aerosol flame speed measurements using LLFAB are compared vs earlier measurements using Bunsen burner and flame tube in microgravity. The developed technique was used to compare the flame speed for pure aluminum and magnesium powders vs flame speed for a set of aluminum-based mechanical alloys using Mg, Ti, Zr, Li, MgH 2 , or C as alloying elements. It was observed that the flame speeds for all of the tested alloys, except the one with carbon, are higher than that of the pure aluminum aerosol.

Mechanical Behaviour and Wear Resistance of Ce-PSZ Alumina Matrix Composites

Abstract. Transformation toughening is one of the methods for improving the strength of alumina which has a hardness value of ~2000 HV. In this study, 0wt.%, 5wt.%, 15wt.%, 25wt.% and 35wt.% of Ce-partially stabilised ZrO 2 powders were dispersed homogeneously in alumina powder matrix. Pure α-Al 2 O 3 and α-Al 2 O 3 /ZrO 2 mixtures were shaped by using slip casting method and then they were sintered at 1550 °C. Specimens were tested in order to determine apparent porosity and bulk density, micro-hardness, flexural strength and fracture toughness. Later, wear tests were carried out on specimens by using 60 and 120 mesh abrasive papers, 64.5N, 33.3N and 14.4N loads. By this procedure, the effects of composition, load and mesh size of abrasive paper on abrasive wear behaviour was inspected throughly. Finally, surface analyses were carried out by using SEM to determine the characteristics of worn specimens. Introduction Alumina ceramics have been widely used materials for their thermomechanical and tribo-properties due to their high hardnesses and ceramical and thermal stabilities. In order to increase the toughness of alumina, a well-known metod is to add PSZ(Partially Stabilised Zirconia) to the matrix. Zirconia increases the toughness of the matrix by several different mechanisms [1-3]. The maximum stress concentration occurs at the tip of the crack. (Fig. 1) [4]. In the dual phased structures, which was ZTA(Zirconia Toughened Alumina) in this case, the fracture energy at the tip of the cracks is absorbed by the transformation thoughness effect of PSZ and prevents the further propagation of the crack (Fig. 2). When the alumina-tetragonal zirconia composites are stressed, the tensile strain field that surrounds a crack tip transforms monoclinic zirconia particles, which expand and generate compressive strain in the matrix and tensile stress at the crack tip is decreased. This stress-induced transformation enhances the fracture toughness of ZTA composites [5]. Zirconia particles dispersed in alumina matrix also increase the fracture toughness, due to the formation of a high density of microcracks absorbing energy due to their slow propagation. The microcracks are formed by the expansion of zirconia during tetragonal to monoclinic transformation. Figure 1. Maximum stress concentration at the tip of the crack [4]. Figure 2. Transformation thoughness of the Ce-PSZ in alumina matrix composite [5]. In this study, different volume percentages of Ce-PSZ powder have been added to pure alumina powder matrix. Then the mixtures were shaped by using slip casting method and the samples were sintered. The abrasive wear properties of the samples were investigated by Pin on Disc type wear test device [6].

INVESTIGATION OF THE SEMISOLID MECHANICAL STIRRING METHOD TO DEPOSIT AN ALUMINUM PARTICLE COATING ON THE SURFACE OF SiC SHORT FIBERS

SiC short fibers, with an average diameter of 13 μm and length of 300–500 μm and chopped from SiC continuous fibers, were surface-modified by the semisolid mechanical stirring method to produce a discrete coating of aluminum particles. The SiC short fibers were introduced into semisolid state aluminum to prepare a slurry by the mechanical stirring method. As all of the short fibers were uniformly dispersed in the slurry, the temperature of the slurry was decreased as quickly as possible, but the slurry continued to be stirred until all of it was converted quickly into a powder-like composite. The surface morphology and axial section of the composite fiber and aluminum particles were examined using a scanning electron microscope (SEM) and an optical microscope; the element analysis of particles on the surface of short fibers in nanometer and submicron sizes was performed by Auger electron spectroscopy (AES). The results indicated that the powder-like composite was a mixture of pure aluminum powder and SiC short composite fiber, the surface of the composite fiber was coated by a discrete single layer of aluminum particles with nanometer, submicron and micron sizes, and the surface coverage of the aluminum particles on the surface of the short fibers ranged from 20 to 30%.

Facet-Defacet Transition of Grain Boundaries in Alumina

Grain boundaries in pure alumina powder compacts sintered at 1400°C are smoothly curved, indicating that they have atomically rough structures. When these specimens are heat-treated at temperatures between 900° and 1100°C, a small fraction of the grain boundaries develop either hill-and-valley or kinked shapes with flat segments. Some of these flat boundary segments lie on the {011[Twomacr]} plane of one of the grain pairs. These grain boundaries thus appear to become singular at these temperatures. When a corundum crystal with a basal surface is sintered in alumina powder at 1400°C, all grain boundaries formed between the corundum basal surface and small grains, as well as those between the small grains, are smoothly curved, indicating their rough structure. When heat-treated at 900°C for 3 days, about 30% of the grain boundaries between the corundum basal surface and the small grains develop kinks with flat boundary segments, and some of these flat segments lie on the basal plane of the corundum. When heat-treated again at 1400°C, all grain boundaries are curved, indicating that they become reversibly rough. These observations show that at least some of the grain boundaries in alumina undergo roughening-singular transitions at temperatures between 900° and 1100°C.

419 純アルミニウム粉がミズナラの表面性状に及ぼす影響(OS コーティング・溶射)

This paper describes about the surface texture of Japanese oak boards. The arithmetical mean roughness value, Ra, the glossiness, and surface color are the three main elements selected for evaluation the surface texture. The surface of Japanese oak boards were filled by pure aluminum powder of different particle diameter. The surface texture after filling was compared to the texture before filling. As a result, the glossiness and the chroma of the filled surface of the Japanese oak boards decreases compared to the texture before filling. Furthermore, when the surface was filled with pure aluminum powder with smaller particle, the glossiness and the chroma tend to decrease more.

Frequency effect on pulse electric current sintering process of pure aluminum powder

Pure aluminum (Al) powder was sintered by means of a pulse electric current sintering (PECS) process at various pulse frequencies. The effects of pulse frequency on the density, electrical resistivity and tensile properties of the compacts were investigated. The results showed that the effects were not significant. From the activation energy calculation in the sintering process and scanning electron microscopy observation of compacts and transmission electron microscopy observation of interfaces between powder particles, the pulse frequency effects on PECS process and microstructure were not observed.

Characterization of Pure Aluminum and Zinc Sprayed Coatings Produced by Flame Spraying

We investigate flame spraying of pure aluminum and pure zinc powders on various different substrates and study shrinkage properties and thermal analysis curves of sprayed coatings during the forming process. We also examined effects of the spray distance on the porosity, tensile strength and hardness of sprayed coatings, and obtained the following results. With an increase in spray distance, shrinkage of the sprayed coating and the maximum temperature in the thermal analysis curve decrease. When the cooling ability of the substrate is higher, the shrinkage ratio and the maximum temperature become decrease. The porosity and the hardness of a sprayed coating increase with an increase in spray distance. This occurs because with the increase in the spray distance, the temperature of the sprayed particles decreases, the amount of air taken in the spray increases and, as a result, the cooling rate of the coating increases. The tensile strength of a pure aluminum coating decreases with an increase in spray distance due to the introduction of pores. On the contrary, the tensile strength of a pure zinc coating increases with an increase in spray distance. This occurs because when the spray distance is short, coating temperature is high and, as a result, a large quantity of zinc oxide is formed.

The Effects of Slider Material on the Gasification of Carbon

The influence of alumina and titanium carbide, components of magnetic recording sliders, on the carbon gasification reaction was investigated. Pure alumina and titanium carbide powders were each combined with graphite powder and subjected to thermogravimetric analysis (TGA). The molar ratio ranged from 0 to 20 mol percent; graphite powder was the balance. From the thermogravimetric analysis, the activation energy Ea of the reactions was determined. It was found that the activation energy for carbon gasification reduced slightly for increasing alumina mole percentage. Titanium carbide additions markedly increased the activation energy. This increase indicates a competitive oxidation reaction that forms titanium oxide, as confirmed by X-ray diffraction (XRD). As a result of these observations, titanium oxide was also mixed with graphite powders and analyzed by TGA. Titanium oxide has an activation energy behavior that becomes more complex with increasing mole percentage: the activation energy first increases and then decreases. These data are presented and the oxidation reaction is proposed.

Preparation and characterization of energetic Al-Mg mechanical alloy powders

Metals such as Al and Mg have high combustion enthalpies and they are widely used as additives in energetic materials for propellants, explosives, and pyrotechnics. However, long ignition delays and slow combustion kinetics limit their current applications. An approach suggested in this work is to design new metal-based materials in which pre-determined phase changes will occur and trigger ignition at a desired temperature and also accelerate the rate of heat release during combustion. As a first step, metastable solid solutions of Mg in Al (10–50% of Mg) have been produced by mechanical alloying. The ignition temperatures of the produced alloys in air were determined using digital imaging and three-color pyrometry of the electrically heated filaments coated with different alloy powders. Combustion of mechanical alloys in air was studied using a laminar, premixed flame aerosol burner. The ignition temperatures were around 1,000 K, much lower than the pure aluminum ignition temperature of about 2,300 K. The steady flames of mechanical alloy powders were produced at lower equivalence ratios and had higher propagation velocities than similar pure aluminum powder flames. Phase compositions of the combustion products were determined using X-ray diffraction. In addition to Al 2O 3 and MgO, significant amounts of Al 2MgO 4 were found in experiments.