Powder Metallurgy and Metal Ceramics (v.48, #5-6)

Hydrodynamic particle-size classification of aluminum alloy powders by O. D. Neikov; I. I. Odokienko; G. I. Vasil’eva; N. G. Chaikina; V. G. Tokhtuev (249-256).
Powder fractionation is an essential part of powder metallurgy processes. However, powder particles smaller than 40 μm can hardly be classified. Meshes with openings smaller than 40 μm are not used in conventional sieving because of very low effectiveness since powder is suspended above the sieve as a result of vibration, which makes it difficult for the particles to pass through the mesh. Powders with particles smaller than 40 μm can be fractionated by hydroclassification. The hydroclassification of aluminum alloy powders and distribution of powder particle sizes are studied, and efficient hydroclassification methods are developed. Water-atomized aluminum powders and alloys have not been produced until recently because of the explosion hazard as hydrogen releases when aluminum interacts with water. A method is proposed for the hydroclassification and, thus, fractionation of powders over a wide range of particle sizes, including those smaller than 40 μm, beginning with 0–10 μm.
Keywords: powder fraction; hydrocyclone; inhibitor; grain-size composition; aluminum alloys

A new model of isotropic materials with different tensile and compressive moduli is proposed. The model is based on a new expression for the three-parameter elastic potential. The parameter responsible for the difference between the elastic moduli is especially significant. The dependence of this parameter on the structure of the materials is established on the basis of micromechanical principles and resistometry. The model is physically nonlinear and permits changes in volume under zero hydrostatic pressure (dilatancy). The shear strains will be zero if so are the shear stresses. The elastic limit criterion is based on the Beltrami hypothesis and is similar to the Cam-Clay condition. The results can apply to powder and damaged materials and soils.
Keywords: elasticity; elastic potential; dilatancy; limit criteria

Compaction and strain hardening of metal powders and their mixtures when pressed by A. K. Radchenko; M. S. Koval’chenko; D. N. Brodnikovskii (267-273).
The compaction of carbonyl nickel powders, nickel-based mixtures, and iron, aluminum, and magnesium powders in cylindrical molds is experimentally studied, the billet height being continuously recorded in a testing machine. The theory of plasticity for powder bodies is used to analyze the strain hardening of the matrix forming a powder body in pressing. It is established that shear yield stress and strain hardening of the matrix determine the shape of the compaction curve and the final density of the powder body.
Keywords: powder; mixture; pressing; compaction; strain hardening

Asymmetric rolling of metal powders. II. Angular parameters of asymmetric rolling by K. A. Gogaev; G. Ya. Kalutskii; V. S. Voropaev (274-278).
The paper examines the angular parameters of asymmetric rolling of powder materials on driven rolls with different diameters but equal angular velocities. The diameter ratio is 1.12 to 1.42. It is established that the mismatch of the velocities greatly influences the angular parameters and promotes shear processes in the deformation zone. To create such conditions, the mismatch between the velocities of the driven rolls should be at least 25%.
Keywords: angles; rolling; powder; asymmetry

Diffusion processes and structurization in microwave sintering of BaTiO3–SrTiO3 and Al2O3–Cr2O3 powder systems with complete miscibility by O. I. Get’man; V. V. Panichkina; P. Ya. Radchenko; V. V. Skorokhod; M. G. Andreeva; A. G. Eremeev; V. V. Kholoptsev (279-289).
The paper examines the compaction and structurization of equimolar BaTiO3–SrTiO3 and Al2O3–Cr2O3 powder mixtures with complete miscibility and monophase Al2O3 and Cr2O3 powders under microwave heating (24 and 30 GHz) (MWH) and conventional heating (CH). A gyrotron system is used for MWH and electric furnaces for CH. The samples are prepared by sintering of ultrafine powder mixtures at 1000–1300°C (MWH) and 1700°C (CH). Mercury porometry is used to determine the mean pore size and specific surface area of the samples. The Barus–Bechgold method is employed to find the maximum pore contraction. A quantitative microscopic analysis of the samples is carried out. The content of solid solution is determined using x-ray analysis. The volume and local shrinkage is calculated. Relationships between the local and volume shrinkage, pore structure parameters, and amounts of solid solutions for different heating conditions are shown. The results reveal different diffusion processes in sintering of powder systems with complete miscibility of components under MWH and CH.
Keywords: microwave heating; sintering; oxide system; microstructure

Vacuum alumina condensates are prepared by electron-beam (at different deposition rates) and pulsed-laser vapor deposition onto polycrystalline molybdenum substrates heated over a wide temperature range. X-ray and electron diffraction and scanning and transmission electron microscopy are used to examine the phase composition, microstructure, and surface morphology of the vacuum condensates. The dependence of the condensate structure on the temperature and deposition rate is established. The experimental data are explained by vapor → crystal or vapor → liquid → crystal vacuum condensation mechanisms depending on the evaporation method. The results permit choosing optimal parameters for the deposition of condensates with needed properties.
Keywords: alumina; vacuum condensates; electron-beam evaporation; pulsed-laser evaporation

Mechanical properties of powder titanium at different production stages. IV. Mechanical properties and contact formation in powder titanium produced by dynamic hot pressing by Yu. N. Podrezov; V. A. Nazarenko; A. V. Laptev; A. I. Tolochin; V. I. Danilenko; Ya. I. Evich; O. S. Koryak (295-301).
The paper examines the effect of hot pressing parameters on the structure and properties of powder titanium. The initial porosity of the compact, sintering temperature and time, and temperature of dynamic hot pressing are varied. The resistivity and mechanical properties are used to assess the quality of the compacts after pressing. It is shown that powder titanium produced under optimal conditions compares well with commercially pure titanium produced with a conventional method.
Keywords: porosity; powder titanium; hot pressing; elastic modulus; conductivity; bending and tensile strength

Iron-based electrode materials for spark restoration of parts by S. M. Kirilenko; O. V. Paustovskii (302-304).
The composition of iron-based electrode material for the spark restoration of steel parts is optimized. The material permits depositing coatings twice as thick as those made of sormite. Varying the content of chromium carbide, one can change coating hardness from 3.9 to 6.8 GPa. The wear resistance of coatings is increased by 20 to 35%.
Keywords: spark coating; deposition; hardness; wear resistance

Effect of cerium dioxide on the properties of biogenic hydroxyapatite sintered with borosilicate glass by L. A. Ivanchenko; N. D. Pinchuk; A. R. Parkhomei; M. E. Golovkova; M. I. Molchanovskaya; A. N. Syabro (305-310).
Samples made of biogenic hydroxyapatite–glass composites containing cerium and lanthanum oxides are produced and examined. The emphasis is placed on composites containing 50.3% hydroxyapatite and 3, 5, or 7% CeO2. It is established that these amounts of cerium dioxide change the color of the samples, somewhat increase their total porosity and compressive strength, and scarcely change their microstructure and solubility in physiological solution. Additions of cerium dioxide have no effect on the biochemical solubility of alloyed samples and thus the use of such materials in surgery to replace bone sections subjected to substantial mechanical loads is beneficial.
Keywords: implant; alloying; color; biosolubility

The structurization of ceramic materials based on SiC–C powder and Al2O3 and Y2O3, and titanium hydride during free sintering and hot pressing is studied. Dispersion hardening of the ceramics with nanosized particles of silicon and titanium carbides is established. The micromechanical properties of the composite materials are examined.
Keywords: solid solution of carbon in β-SiC; synthesis; alumina; yttria; eutectic; titanium hydride; sialon; mullite; free sintering; hot pressing; dispersion hardening; ceramic composite

To improve the abrasive wear resistance of titanium alloys, ZrB2-containing protective coatings are deposited by electrospark alloying (ESA). As electrode materials, composite ceramics with different amounts of ZrB2 are used. Some of the coated samples are also subjected to laser treatment to improve the coating by structuring the surface as alternating laser fusion tracks and nonfused sparkdeposited areas. The microstructure and phase composition of the coatings are characterized. The surface layer of the worn laser fusion tracks is found to have increased hardness (up to 22–38 GPa), which is two to four times higher than that of the surface before abrasion (~9.5 GPa).
Keywords: spark-deposited coating; laser fusion; zirconium diboride; structural and phase transformations; hardness

Thermodynamic properties of silicon-rich holmium silicides by L. V. Goncharuk; V. R. Sidorko; Yu. I. Buyanov (326-329).
The free Gibbs energy, enthalpy, and entropy of formation of silicon-rich holmium silicides HoSi2–a (HoSi1.82), HoSi2–b (HoSi1.67), Ho3Si4, and HoSi from solid components are determined by measuring electromotive forces between 710 and 930 K. The thermodynamic functions of formation of HoSi1.67 and Ho3Si4 from individual components are determined for the first time.
Keywords: thermodynamic properties; Gibbs energy; enthalpy; entropy; holmium; silicon

High-temperature and electrochemical oxidation of transition metal silicides by A. D. Chirkin; V. O. Lavrenko; V. M. Talash (330-345).
High-temperature and electrochemical oxidation of transition metal silicides, which are widely used in microelectronics as ohmic contacts and protective coatings for high-temperature alloys, are discussed in this review. The process of oxide film formation during annealing or anodizing is extremely important for both applications of silicides. It is discussed for three disilicides: MoSi2, WSi2, and TiSi2. It has been shown that different types of oxide films may form on the disilicide surface depending on the thermodynamic (formation enthalpies of silicides and associated oxides) and kinetic (diffusion coefficients of silicon in silicide and oxygen diffusivity in oxide) factors: onephase (MoSi2), mixed (WSi2), and multilayer (TiSi2) films. The “silicide pest” phenomenon is discussed in terms of thermodynamic, kinetic, and structural factors influencing the pesting. Analysis of electrochemical oxidation mechanisms for silicides in various electrolyte media reveals numerous similarities between anodic and high-temperature oxidation mechanisms. It is shown that slow silicon transport during anodic treatment at room temperature leads to the formation of multiphase mixed oxide films under electrochemical polarization.
Keywords: transition metal silicides; kinetics of high-temperature oxidation; formation mechanism; protective oxide films containing SiO2 ; anodic electrochemical oxidation; electrolyte solutions

Composites based on aluminum and boron nitrides formed during hot pressing by O. N. Grigor’ev; N. D. Bega; T. V. Dubovik; O. D. Shcherbina; V. I. Subbotin; A. A. Rogozinskaya; L. A. Klochkov; I. L. Berezhinskii; V. E. Matsera; V. V. Lychko; P. V. Mazur (346-352).
The paper examines how MoSi2, ZrO2, and SiO2 additions influence the phase formation and properties of hot-pressed AlN–BN (АBN) composites. It is established that new hardening phases are synthesized in the hot pressing of composite materials. The developed composites have higher strength than sintered ABN and retain oxidation resistance, excellent electrical insulation properties, and good machinability.
Keywords: aluminum nitride; boron nitride; molybdenum silicide; silicon oxide; zirconium oxide; hot pressing; phase formation

Far infrared properties of sintered Pb0.9Sn0.1Te doped with palladium by P. M. Nikolic; K. M. Paraskevopoulos; M. V. Nikolic; S. S. Vujatovic; E. Pavlidou; T. T. Zorba; T. Ivetic; B. Stamenovic; N. Labus; M. Jovic; M. M. Ristic (353-357).
Far infrared reflectivity spectra of sintered Pb0.9Sn0.1Te doped with 0.2 and 2 at.% Pd are measured. The experimental results are analyzed using a fitting procedure based on a modified plasmon-phonon interaction model. The values of calculated parameters are compared with literature data for PbTe and PbSnTe single crystal samples doped with palladium and nickel, with the purpose of determining whether the sintered samples can be used in different devices instead of single crystals.
Keywords: far infrared reflectivity spectra; palladium; lead; sintering; single crystals

Structural and phase transformations in the tribosynthesis area of copper-based self-lubricating composite material by A. G. Kostornov; O. I. Fushchich; T. M. Chevychelova; A. Yu. Koval’; A. D. Kostenko (358-364).
The paper examines the structural self-organization and adaptation of the surface layers of self-lubricating composite antifriction material (SCAM) IPM-304 to friction conditions. It is shown that temperature jumps and elastoplastic deformation are observed in the tribological contact area in SCAM performance in vacuum under friction. These factors and the difference in thermal expansion coefficients of the matrix and lead, for example, cause partial melting, isolation, layer-by-layer change in shape and size, plasticization, and rearrangement of the antifriction and reinforcing components in thin layers of the friction surface. This results in layer-by-layer changes in the chemical and phase composition, structure, and mechanical properties of surface layers. That is, tribosynthesis proceeds on the material layer responsible for the improvement of SCAM tribotechnical characteristics: decrease in friction coefficient and increase in wear resistance.
Keywords: self-lubricating antifriction composite material; composition; structure; synthesis; mechanism; temperature; melting; localization; rearrangement; plasticization; structural self-organization; friction coefficient; wear resistance; mechanical properties

Nanosized iron and iron oxide powders promising for medicine by T. E. Babutina; N. V. Boshitska; O. A. Ivashchenko; A. O. Perekos; V. Z. Voinash; I. V. Uvarova (365-370).
Nanosized iron-based powders of different compositions and particle sizes have been developed for medical application. It is shown that their structural and phase compositions, which are related to their magnetic properties, can be controlled. The interaction of the powders with model media such as human blood plasma and its mixture with 0.9% NaCl solution (1:1), distilled water, and 0.9% NaCl solution is studied. The rate of powder dissolution in blood plasma is established to depend on the α-iron content and particle size: the higher these parameters, the more intensive the powder biotransformation. The Fe3O4 powders are quite resistant to model biomedia: their solubility in media containing blood plasma is one-hundredth to seven-thousandths of α-Fe solubility.
Keywords: iron nanopowder; medical application; magnetic properties