Pure Metal Powders Research Articles

CENTRIFUGAL FORCE ASSISTED COMBUSTION SYNTHESIS OF INTERMETALLICS (NiAl)

A novel method, developed for the simultaneous combustion synthesis and densification of an intermetallic, has been described. In this method, a highly exothermic reaction (or a chemical oven) is used as a source of heat for combustion synthesis and centrifugal force is used as a source of pressure for simultaneous densification. Known quantities of pure metal powders were melted by this method using thermit reaction (Fe2O3+2Al→Al2O3+2Fe) as the source of heat to establish the range of sensible heat, H s, available for combustion synthesis of an intermetallic under the experimental conditions employed in this study. Castings of equiatomic NiAl were produced, using powders of the constituent elements, in this range of H s at different magnitudes of centrifugal force. The adiabatic temperature of the reaction Ni+Al→NiAl was estimated. At all the magnitudes of centrifugal force studied, the density of NiAl was found to increase with the increase in H s and reach a maximum when conditions were nearly adiabatic. The variations in the centrifugal pressure and heat transfer during the synthesis of NiAl were found responsible for this change in density.

Preparation of W–Al alloys by mechanical alloying

W 1− x Al x ( x=0–0.86) alloys were synthesized by mechanically alloying the pure metal powder mixtures at designated compositions by conventional high-energy ball milling. The W–Al alloys were stable under high pressure and high temperature. The alloys were lighter than W. The hardness and oxidation resistance of the alloys was greatly improved compared to both W and Al.

First Trial of Pulse Electric Current Sintering for High-Temperature Material Ir<SUB>3</SUB>Nb

Pulse electric current sintering (PECS) was tried for Ir-25 at.% Nb (Ir3Nb), which has a high melting temperature of about 2435 °C. Ingot powder was made by crashing an ingot, and the ingot powders were sintered at temperatures between 1700 and 1900 °C up to 2 h under 40 MPa. Pure-metal powder was mixed to achieve a composition of Ir-25 at.% Nb, and the pure-metal powders were sintered at a temperature between 1700 and 1900 °C for up to 1 h. The microstructure and phase structures of sintered samples were investigated by scanning electron microscopy (SEM) and x-ray diffractometry. The sintering mechanism and problems for Ir3Nb in PECS are discussed.

Textural Characterisation of Iron-Promoted Raney Nickel Catalysts Synthesised by Mechanical Alloying

Mesoporous binary AlxNiy and ternary AlxNiyFez Raney-type catalysts were synthesised by a two-step procedure involving two main processes, i.e. (i) mechanical metal alloying and (ii) alkaline aluminium leaching. Pure metallic powders of Al, Ni and Fe (if required) were first mechanically alloyed in an attrition mill and then subjected to KOH leaching to selectively remove part of the aluminium atoms. After a slow drying process, a fine, nanostructured slit-shaped material was obtained. Substrate characterisation involved studies by atomic absorption (AA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDXS) in the SEM and nitrogen physisorption. An intermetallic β- or B2-(AlNi) phase with a metastable bcc crystalline structure was formed as a non-equilibrium phase after the metal alloying process. Because of aluminium removal, the β-(AlNi) phase was transformed into the more stable nickel fcc structure. In this work, some important physicochemical proper...

Densification of mixed metal powder at high temperature

Densification behaviors of mixed metal powder under high temperature were investigated. Experimental data of mixed copper and tool steel powder with various volume fractions of Cu powder were obtained under hot isostatic pressing and hot pressing. By mixing the creep potentials of McMeeking and co-workers and of Abouaf and co-workers originally for pure powder, the mixed creep potentials with various volume fractions of Cu powder were employed in the constitutive models. The constitutive equations were implemented into a finite element program (ABAQUS) to compare with experimental data for densification of mixed powder under hot isostatic pressing and hot pressing. Finite element calculations by using the creep potentials of Abouaf and co-workers agreed reasonably well with experimental data, however, those by the model of McMeeking and co-workers underestimate experimental data as observed in the case of pure metal powders.

Preparation of iron–nickel catalysts by mechanical alloying

Raney type catalysts were prepared by means of a two-step procedure: (i) mechanical alloying (MA) of the metals and (ii) alkaline aluminum leaching. MA is a novel alternative related to the synthesis of skeletal Ni catalysts. Catalyst characterization was performed by atomic absorption (AA), X-ray diffraction (XRD), and Mössbauer spectroscopy (MS). Textural studies were also carried out. Binary Al–Ni and ternary Al–Ni–Fe alloys were produced by MA from pure metallic powders; in particular, the intermetallic β-(AlNi) phase was formed with a fine microstructure as a non-equilibrium phase; then, aluminum was selectively removed. After aluminum leaching, the β-(AlNi) phase was transformed into the more stable nickel fcc structure.

X-Ray Diffraction and Mössbauer Characterization of Raney Fe-Ni Catalysts

Rancy type catalysts were prepared by means of a two step procedure: (1) Mechanical alloying of the metals and, (2) alkaline aluminum leaching. Mechanical alloying is a novel atlernative related to the synthesis of skeletal Ni catalysts. X-ray diffraction, and Mossbauer spectroscopies were performed for catalysts characterization. Binary Al-Ni and ternary Al-Ni-Fe alloys were produced by mechanical alloying from pure metallic powders; in particular, the intermetallic β-(AlNi) phase was formed with a fine microstructure as a non-equilibrium phase; then, aluminum was selectively removed. After aluminum leaching the β-(AlNi) phase was transformed into the more stable nickel fee structure.

Non-Destructive Determination of Silicon in Steel and Steel-Related Samples by INAA Using the 29Si(n,p)29Al reaction

A non-destructive method has been developed for the determination of silicon in steel alloys by reactor fast neutron activation analysis using the 29Si(n,p) 29Al reaction. An iron sample and a comparator of pure metallic silicon powder are irradiated in a cadmium case. In order to obtain the net counting rate of the 1273.4 keV peak from 29Al, background activities are corrected carefully to avoid peaks of 1268.0 keV from 28Al single-escape and 1266.2 keV from 31Si. The present method is superior to the method using the 28Si(n,p) 28Al reaction.

Nano-structured intermetallic compound TiAl obtained by crystallization of mechanically alloyed amorphous TiAl, and its subsequent grain growth

The amorphization process during mechanical alloying (MA) was investigated for the Al-50at%Ti and Al-50at%Ti-10vol%TiB2 powder mixtures. Pure metallic powders of Al and Ti were finely mixed and transformed to the amorphous phase after being milled for about 2880 ks. In the case of Al-50at%Ti-10vol%TiB2 powder, the amorphous alloys with a fine dispersion of TiB2 particles could be obtained for a shorter milling times than that required for the powders without TiB2 ceramics. As a result of heat treatment for the mechanically alloyed amorphous powders, a nanocrystalline intermetallic compound of TiAl (γ) could be produced. Subsequent grain growth of the γ phase during heat treatment was investigated by estimating the grain-growth exponent and the activation energy for grain growth. It was found from this estimation that the grain growth was further suppressed as the powders were mechanically alloyed for longer times. Furthermore, the addition of the TiB2 particles that could be dispersed during MA finely and homogeneously in the amorphous matrix was found to be effective for suppression of the γ grain growth especially at elevated temperatures as well as for a long annealing.

X-ray diffraction characterisation of carbide and carbonitride of Ti and Zr prepared through reaction between metal powders and carbon powders (graphitic or amorphous) in a solar furnace

Non-stoichiometric carbide MC x (0.5 < x < 1) and carbonitride MC x N y (0.5 < x + y < 1) of IVa-group metals (M=Ti and Zr) were synthesised from compacted mixture of pure metal powders and carbon powders (graphite or amorphous carbon) under 30 min solar radiation at measured temperature around 1600°C. X-ray diffraction analysis of the reaction products showed that the composition x in MC x and x and y in MC x N y varied depending on whether the carbon was graphite or amorphous carbon like in the case of similar synthesis in traditional laboratory furnace. In the present work, no evidence of graphitisation of amorphous carbon was observed unlike in the case of solar carbide synthesis of some VIa-group metals (Cr and W).

Mechanical alloying of Ti-Ni alloys under high pressure

The formation and properties of amorphous alloys have been the subject of a large amount of research. Amorphous alloys have been obtained in recent years by rapid quenching from the liquid state or by mechanical alloying in a planetary mill. Moreover metals and alloys in amorphous or nanocrystalline states can be processed by intense plastic deformation under high pressure. One advantage of this method is that it makes it possible to obtain new materials from powders of different elements, which are immiscible in the liquid state. At the present time, investigations devoted to producing amorphous alloys by mechanical alloying under high pressure are still scarce. So the primary purpose of the present research was to study the microstructure and phase constitution of Ti-Ni alloys produced from powders of pure metals by mechanical alloying under high pressure.

Production of highly dispersed metal powders by electrical explosion in reduced-pressure nitrogen

It is suggested that nitrogen may be used as the ambient medium to obtain highly dispersed powders of pure metals. At reduced pressure nitrogen is chemically inert and has a higher dielectric strength than rare gases. A reduction in the gas density reduces the particle size of the pure metal powder down to the nanometer range.

Physicochemical and catalytic properties of iron-promoted Raney-nickel catalysts obtained by mechanical alloying

Raney‐type catalysts were prepared by means of a two‐step procedure: (i) mechanical alloying of the metals and (ii) alkaline aluminum leaching. Mechanical alloying is a novel alternative related to the synthesis of skeletal Ni catalysts. Catalysts characterization was performed by atomic absorption, X‐ray diffraction, electron microscopy, and Mossbauer spectroscopies. Textural studies were also carried out. Binary Al–Ni and ternary Al–Ni–Fe alloys were produced by mechanical alloying from pure metallic powders; in particular, the intermetallic α‐(AlNi) phase was formed with a fine microstructure as a non‐equilibrium phase; then, aluminum was selectively removed. After aluminum leaching the α‐(AlNi) phase was transformed into the more stable nickel fcc structure. The effect of iron addition to the Ni–Al catalysts depends on iron concentration and reduction temperature; both parameters determine catalysts composition and activity. This work reports physicochemical properties and benzene hydrogenation activity of these materials, compared with conventional catalysts obtained by melting and leaching.

Infiltration-Diffusional-Solidification (IDS): A P/M+Liquid Metal Infiltration Route for Processing Metal Matrix Composites

A process for the production of MMCs, based on the infiltration by a low melting temperature eutectic alloy of porous preforms containing a mixture of reinforcing ceramic particles and pure metal powder is described., The infiltration is done at temperatures higher than the eutectic temperature, but below the fusion temperature of the pure metal. After infiltration with the low melting temperature liquid, a diffusional solidification process occurs, where the solidification is controlled by the partition of the alloying elements between the solid and the melt. Preforms prepared with mixtures of Al powders and SiCp, were cold pressed to different pressures so as to obtain from 25% to 10% volume fractions of pores. The compression curves obtained are described. Infiltration experiments using eutectic Al-Cu alloys (33%weight Cu) and Zamak 5 (Zn-4% Al- 1%Cu) were run on the preforms, varying the infiltration pressure and the cooling rate after infiltration. Infiltrated samples were microstructurally characterized by optical and scanning electron microscopy. The final structures showed that the IDS concept is feasible, producing MMC's with homogeneous matrixes and regular distributions of SiCp.

Infiltration diffusional solidification: a new route for processing metal matrix composites

An alternative route for the production of particle reinforced MMCs by infiltration with any volume fraction of particles up to ∼50% is described. The process is based on the infiltration by a low melting temperature eutectic alloy of porous preforms prepared with a mixture of the reinforcing ceramic particles and a pure metal powder. The infiltration is done at temperatures above the eutectic and below the fusion temperature of the pure metal; Once infiltrated with the eutectic, the solidification can proceed with a planar front and it is controlled by the partition of the alloy elements between the solid powder and the melt. Experimental results show that a homogeneous spatial distribution of reinforcement particles in the MMC can be achieved, provided that the reinforcement particles are the same size as the pure metal powder.

Polymer Matrix Influence on the Kinetics of Some Fundamental Inorganic Colloidal Reactions

Among the most useful methods for the preparation of pure metal powders is the thermolysis of metal carbonyl complexes in hydrocarbon solutions. Zero-valent cobalt particles are obtained by the decomposition of Co2(CO)8. The reaction is primarily governed by diffusion, which is strongly dependent on the viscosity of the solution. In a solution containing polystyrene, the viscosity is directly proportional to the concentration of the polymer. To study the variation of the rate constants of this colloidal reaction as a function of the solution viscosity, we examined various polystyrene solutions of different molecular weights and concentrations. The reaction rate increases considerably at polymer content below and at the critical coil overlap concentration. Above this concentration, as the polymer coils become entangled and contracted, the decreased mobility of the molecules due to higher viscosity and lower diffusion rate lowers the reaction rate. The influence of the molecular weight of the polystyrene on the reaction kinetics had a “catalytic” effect on reaction rates and was most dramatic with a MW(avg) of ∼120 000. We find that in the dilute polymer regime, below the PS coil overlap threshold, the polymer chains can provide the necessary support for the aggregation of the cobalt particles. Also, in the dilute regime, the mobility of the cobalt molecules is not hindered due to the low solution viscosity. However, there is evidently a critical molecular weight at which the “catalytic” effect of the polymer is at its maximum. These results will be discussed, and possible mechanisms for the polymer-enhanced colloid reactions will be offered.

Development of a thick wear-resistant jet kote coating produced at high

The JET KOTE coating process is a high-velocity oxyfuel process used to form coatings of high quality and density. Coatings can be produced from carbide-bearing composite, alloyed metallic, nonmetallic, intermetallic, or pure metal powders. The coatings are used for wear and/or corrosion resistance in the aircraft, chemical, oil and gas, and steel manufacturing industries, as well as in other demanding fields. Many applications, especially in the petrochemical field, require thick coatings. Coatings must be applied economically, without loss of integrity. Thickness limitations are thought to be due to coating stress, which results in coating cracks and/or delamination and ultimately in failure. This paper examines the effects of operating parameters and techniques on the physical properties of thick coatings produced from Stelcar JK117, a tungsten carbide/17 % Co composite powder. Special emphasis is placed on those parameters which are economically desirable to achieve high deposition rates.

The influence of FeTi and NiTi intermetallide additions on high-temperature oxidation of permalloy alloy

As a rule powder metallurgy Permalloy alloys are used in production of parts for electronic instruments. For the purpose of controlling the magnetic and electrical properties and also the wear (in the case of production of magnetic heads) and corrosion resistance appropriate additions of metals or such compounds as carbides and oxides are added to the alloy. In this work use of FeTi and NiTi intermetallides produced by reaction sintering of powders of pure metals in a protective atmosphere as alloying additions to Permalloy is recommended. The size of the original powders is less than 100 {mu}m. For reaction sintering at temperature 50{degrees}C above the eutectic temperature in the Ti-TiFe and TiNi-Ni systems was selected. The contents of titanium, iron, and oxygen in the FeTi alloy is 51.9, 45.7, and 2.4 wt.%, respectively, and of titanium, nickel, and oxygen in the NiTi alloy 59.6, 31.9, and 4.6 wt.%. High-temperature oxidation in air up to 1300{degrees}C with a rate of change in temperature of 15{degrees}C of type 78N Permalloy with additions of FeTi and NiTi alloys was investigated with use of methods of differential thermal and differential thermogravimetric analyses on an OD-103 derivatograph under nonisothermal conditions. The reaction products were studiedmore » by x-ray diffraction phase analysis on a DRON-3 instrument in CoK{sub {alpha}}-radiation. Pure 78N alloy powder with a composition of 78.1% Ni + 19.3% Fe (specimen 1) and also with additions of 1% FeTi (specimen 2) and 1% NiTi (specimen 3) were subjected to oxidation.« less

Thermal behaviour of amorphous Cu xZr 1− x powders synthesized by mechanical alloying

Pure metal powders of copper and zirconium mixed in various atomic ratios were mechanically alloyed by laboratory ball milling in an inert atmosphere. The progress of the amorphization reaction by mechanical alloying was monitored by means of X-ray diffraction. The samples exhibited similar reaction rates, namely a second order reaction. The thermal behaviour of the amorphous Cu x Zr 1− x powders synthesized by mechanical alloying has been studied by differential thermal analysis (DTA), X-ray diffraction and the measurement of electrical resistance. The resistivity behaviour was correlated with the thermal behaviour of DTA. It was found by means of X-ray diffraction that the thermal behaviour was related to the crystallization of the amorphous sample.

Investigation on the kinetics of thermal decomposition of calcium carbonate

The grain model is applied for cylindrical pellets with transient heat and mass transfer equations assuming spherical grains. Small quantities of pure metallic powders when added as additives to the parent material considerably altered the rate of decomposition. Further, experiments were carried out with black coated pellets to enhance the surface heat absorption and results have been presented and discussed qualitatively