Powder producing processes and properties
Naiden E.P., Itin V.I., Magaeva A.A., Terekhova O.G., Kostikova V.A., Zagrebin L.V., Shestov S.S.
The effect of conditions of mechanochemical synthesis and heat treatment on phase composition, structural parameters, and magnetic properties of nanosized powders of cobalt ferrospinel
Nanosized cobalt ferrospinel powders have been obtained with using mechanochemical synthesis from salt systems. X-ray crystallography, TEM, and X-ray fluorescence analysis were used for investigation of the effect of duration (τ) of mechanochemical synthesis and temperature (t) of subsequent thermal treatment on the phase composition, structural parameters, and the main magnetic properties of cobalt ferrospinel. Its yield and average dimension of nanoparticles is found to increase and the area of specific surface and internal elastic stresses decrease so far as τ and t rise. In such a case, the saturation magnetization rises and the change of effective field of magnetic anisotropy is of more complex kind and caused mainly by decrease of a contribution of magnetic elastic component to the total energy of magnetic material.
Key words: oxide nanoferrimagnetics, mechanochemical synthesis, magnetic properties, nanosized powders.
Svistun L.I., Dmitrenko D.V., Pavlygo T.M.
Steel-carbide mix material preparation process
Kinetic dependences of average dimension of carbide and steel particles have been studied in grinding in an attritor. A volume content of different fractions in studied powders is established. Powder charge mixtures process for production of 40Kh2–В4Ñ, R6M5K5–TiC and Kh18N15−Сr3C2 steel-carbide used for production of machine-building parts to operate under the conditions of increased wear, high temperature, and aggressive media is given.
Key words: composite material, powder metallurgy, steel-carbide, charge mixture, grinding, fine crushing, process flow diagram.
Zolotukhina L.V., Kuznetsov M.V., Gelchinsky B.R., Zhidovinova S.V., Arefiev I.G.
Investigation of surface of ultrafine copper powder particles produced by gas-phase condensation
Ultrafine copper metal powders produced according to the evaporation–condensation process have been investigated. Depending on evaporation rate, different dispersiveness and degree of agglomeration of copper powders are shown to be reached when copper mass fraction in them remains unchanged at the level of no lower than 99,0 %. The XPS shows CuO oxide layer of 5–6 nm thick on the surface of Cu-particles as well as outer Cu2O layer ≤1 nm thick for all the powders being analyzed. It is assumed that copper surface layer oxidation to Cu2O lower oxide takes place because of low residual air pressure in the industrial plants when metal evaporates, and CuO oxide is formed as a result of Cu2O decomposition in the process of copper particles condensation. The oxide content in powder is the higher the smaller is the size of its particles.
Key words: metal powders, gas-phase synthesis, oxide layer, XPS.
Sidorova E.N., Samokhin A.V., Kornev S.A., Dzidziguri E.L., Grozdova I.V., Korovkina N.F.
Dimensional features of copper nanopowders before and after production
Using electron microscopy and X-ray diffractometry, the dimensioning specifications of copper nanopowders produced by plasmachemical synthesis have been studied. Metal and oxide samples have been investigated. Average sizes of particles and coherent-scattering regions are determined, and histograms of particles and coherent-scattering regions by sizes are plotted. Nanopowder dimensioning specifications before and after oxidation are compared.
Key words: nanopowders, particle size, coherent-scattering region.
Yedrennikova E.E., Vorobieva M.V., Ivanov V.V., Rakova N.N.
Study of kinetics and characteristic properties of ammonium paramolybdate reduction in hydrogen-nitrogen media
The kinetic features of ammonium paramolybdate reduction in hydrogen and hydrogen-nitrogen mediums at their 1 : (0,5?1,0) ratio have been studied in a temperature range of 250–950 °C and at gas supply rate of 1–3 l/min. The optimal conditions of the process in hydrogen-nitrogen media ensuring target phase extraction no less than 90 % are established. The evolution of nano- and microcrystalline molybdenum powders by ammonium paramolybdate reduction in hydrogen-nitrogen steam-gas media is investigated. Reduction atmosphere type dependence of grain-size distribution and morphology of produced powder samples is shown. A great number of crystallization centers with formation of molybdenum grains by pseudomorph transformation is observed in powders at high-temperature (880–900 °C) reduction in the hydrogen-nitrogen steam-gas medium (1 : 1 ratio).
Key words: powder, molybdenum, ammonium paramolybdate, reduction, hydrogen-nitrogen steam-gas medium.
Theory and processes of powder material formation and sintering
Fedotov A.F.
Plasticity condition of powder material with strain-hardening solid phase
Considering the dual mechanism and local character of particle straining, the plasticity condition of powdered material with strain-hardening solid phase is proposed. Plastic deformation localization is considered by accepting the hypothesis on formation of plastic and elastic volumes in solid phase. The average-out of microscopic plastic stresses and strains takes place only across the plastic volume. The offered plasticity condition ensures high accuracy of the approximation of experimental compaction curves at the stages of interparticle slip and plastic straining of particles. As this takes place, at the beginning moment of plastic deformation the particle material is considered as cast material, which has been already plastically strained and hardened to the magnitude of the effective yield stress of the powder solid phase. Thereafter, the particle material hardening occurs according to the cold-worked cast material hardening. Good conformity of the design and test data is obtained in straining the powders according to the isostatic compression and upset diagrams in a high pressure chamber.
Key words: powdered material, plasticity condition, deformable volume, strain hardening.
Self-propagating high-temperature synthesis
Minin R.V., Itin V.I., Naiden E.P., Zhuravlev V.A.
Regularities of self-propagating high-temperature synthesis, phase composition, and magnetic properties of complex oxide ferrimagnetics with M-structure
The regularities of reagent mixture burning that forms complex oxide ferrimagnetics – hexaferrites with M-structure have been examined. The phase composition of finished product depending on the technological condition including self-propagating high-temperature synthesis as well as that with preliminary mechanical activation and/or the subsequent ferritizing has been established. The basic static and dynamic magnetic properties of the main product synthesized at the optimum conditions are determined. The energy-saving process of hexaferrites with M-structure is proposed, thus allowing us to essentially reduce the industrial expenditures.
Key words: hexaferrites, self-propagating high-temperature synthesis (SHS), mechanical activation, magnetic properties.
Amosov A.P., Latukhin E.I., Fedotov A.F., Yermoshkin A.A., Altukhov S.I.
Production of multicomponent SHS-compacted cathodes on the basis of refractory titanium compounds for application of vacuum-arc coatings
Technological features and a device for manufacture by SHS-method of multicomponent cathodes of electric arc evaporators are considered. SHS-compacted cathode represents a four-layered functionally-gradient article and consists of metal base having the water-cooled ground part of regular cathode, working layer to be evaporated, interlayer and SHS-braze necessary for connection of the synthesized material to the base. Compositions and mass characteristics of the layers to ensure faultless multicomponent SVS-compacted cathodes on stainless steel ground are given.
Key words: multicomponent cathode, electric arc evaporator, SVS-compaction, multilayered article.
Refractory, ceramic and composite materials
Vorozhtsov S.A., Buyakova S.P., Kulkov S.N.
Synthesis, structure, and phase composition of Al–Al4C3 nanostructural materials
The morphology and phase composition of nanocrystalline aluminum and carbon powders in the form of cluster diamonds have been investigated. It has been found that hot compaction of C–Al nanocrystalline powder composition is accompanied by formation of Al4C3 phase of highly refined structure. The mean crystallite size in hot-compacted materials is 40 nm for metal matrix and 30 nm for aluminum carbide. The pore volume in produced hot-compacted materials is shown to increase when carbon portion in starting mixture powders rises.
Key words: composite material, aluminum, carbon, cluster diamond, aluminum carbide.
Baglyuk G.A., Napara-Volgina S.G., Mamonova A.A., Orlova L.N., Kud’ V.K.
Dependence of properties of sintered boron-containing steels on conditions of synthesis and content of foundry alloys
The article gives the results of the investigation concerning the effect of process parameters of powdered boron-containing foundry alloy synthesis on their chemical and phase compositions as well as the content of foundry alloy additives in powder mixture on the structure and properties of sintered steels produced with their application. Application of more dense briquettes compacted at pressure ≥ 700 MPa is shown to allow reducing considerably boron evaporation in the course of foundry alloy synthesis via the gas phase by contrast with briquettes compacted at lower pressures. Application of elevated temperature (1200 °С) for foundry alloy synthesis results in denser material after sintering and consequently raised strength properties. Increase of boron content in primary mixture results in hardening and reduction of sintered steel strength while after heat treatment the boron content dependence of strength has a maximum at boron content of ~ 0,8 %.
Key words: powder steel, boron carbide, foundry alloy, thermal synthesis, sintering.
Porous materials and biomaterials
Levchenko V.S., Plotnikov A.S., Yermilov A.G., Bogatyryova E.V.
Porosity of compacted materials produced from organo-metal compounds
The possibility to produce highly porous (60–80 % of pores) materials by combination of procedures of powder metallurgy with chemical-metallurgical processes to form nanosized sintering activators during thermal destruction of organo-metal compounds is shown. Irrespective of makeup of initial mix materials the surface porosity of such materials is described by pores <30 μm, which portion does not exceed 1 %. Pores < 4 μm represent the basis (86–89 %). The character of porosity inside sintered products is determined by the sizes and shape of the powdery frame material being entered into initial mix materials to prevent outflow of organo-metal compound in the course of heat treatment. In using powders with strongly developed particle surface, the character of inner porosity is close to the superficial one. The combination of scaly particles <100 μm in size and finely divided (<10 μm) particles promotes formation of long pore channels (100–350 μm) of 10–50 μm wide.
Key words: highly porous material, character of porosity, organo-metal compounds, frame powdery material, micropores, pore channels.
Surface modifying, including by charged beams, photon and plasma fluxes
Stepanova I.V., Panin S.V., Durakov V.G., Korchagin M.A.
Modification of structure of powder coatings on nickel and chromium-nickel bases by introduction of titanium diboride nanoparticles during electron-arc weld deposition
Recently composite materials and coatings containing TiB2 nanoparticles in metal matrix are being widely investigated for the purpose of high-strength materials being persistent to high temperatures. Because of high hardness, heat and corrosion resistance, titanium diboride is a perspective compound for using as a wear-resistant component of "metal matrix – TiB2" compositions. We investigated the structure and mechanical properties of (Ni–Fe–Cr–Si–B)–TiB2 and (Ni–Cr)–TiB2 compositions produced by three-stage technique: preliminary mechanical treatment of elemental powder mixtures, SHS-reaction ignited in the treated mixture, and subsequent machining process of SHS-reaction product. Electron-beam surfacing was used for producing coatings.
Key words: self-propagating high-temperature synthesis (SHS), mechanical activation, nanostructure titanium diboride, wear-resistant thermalbarrier coatings, electron-beam weld deposition.
