Powder production processes and properties

Kostikov V.I., Dorofeev Yu.G., Yeremeyeva Zh.V., Zherditskaya N.N., Ulianovsky A.P., Sharipzyanova G.Kh. Characteristic properties of utilization of nontraditional carbon-containing components in powdered steel technology
Report 1. The effect of unconventional carbon-containing components on the processes of charge material preparation and powdered steel rough piece compaction
Powdered carbon steel sintering processes are analyzed in introducing nonconventional carbon-containing components (artificial special low-ash graphite, pyrocarbon, high-temperature coal-tar pitch). The characteristic properties of chemical composition and powder grading as well as crystalline structure of these components as compared with traditionally used pencil lead are shown to cause the acceleration of material homogenization in sintering, improvement of its structure characteristics, and increase of the mechanical properties.
Key words: carbon-containing components, artificial special low-ash graphite, high-temperature coal-tar pitch, pyrocarbon, charge material, sintering, shrinkage, tensile tests.

Kasimtsev A.V., Levinsky Yu.V., Zhigunov V.V. Production of composite Ni-Ti powder by titanium nickelide carbidizing treatment
The work objective is studying the mechanism and kinetics of titanium nickelide powder carbidizing treatment to produce Ni-TiC composite powder. Using experimental techniques and theoretical analysis it has been found that the process within a temperature range of 1000-1200 °С proceeds in the internal mode followed by NiTi decomposition and nickel based solid-solution formation with dispersed titanium carbide particles distributed in it. In case of carbon surplus in the initial charge mixture, the final product is shown to consist of nickel matrix comprising ~ 3 at. % carbon and trace titanium; the particles are practically of stoichiometric titanium carbide. In case of carbon deficiency in the initial charge mixture, Ni-matrix contains ~ 1·10-2 at. % carbon and >0,65 at. % titanium; and titanium carbide particles have the composition of TiC_0,5 -TiC_0,8. The proposed process model permits to estimate the time of complete decomposition of NiTi particles and describe qualitatively the time dependence of titanium carbide particle size.
Key words: composite powder, titanium nickelide carbidizing treatment, kinetics, equilibrium.

Kasimtsev A.V., Zhigunov V.V., Tabachkova N.Yu. Composition, structure, and properties of hydride calcium titanium carbide powder
Titanium carbide particle technology has been developed by using titanium dioxide reduction-carbidizing treatment with calcium hydride and carbide at temperatures under 1200 °С. Dispersity of TiC particles was determined by thermal desorption and scanning electron microscopy: average crystal size does not exceed 1 µm. Coulometry and energy-dispersive spectrometry have found hydride-calcium titanium carbide to be characterized by high content of combined carbon and low content (0,01-0,03 wt %) of free carbon. X-ray diffraction analysis and transmission electron microscopy have found TiC particles to be homogeneous (their composition is close to stoichiometric TiC1.0) and to be monocrystals. Investigation of the structure and properties of the alloys having compositions of 60%ТiС + 29,6%Ni + + 10,4%Мо and 72%ТiC + 18,3%Ni + 9,7%Мо and produced on the basis of found hydride-calcium titanium carbide powders has shown they to meet in full the requirements imposed to tungsten-free hard alloys.
Key words: titanium carbide, hydride-calcium technique, monocrystal, dispersity of powder, hard alloys.

Andreev E.I., Glavin K.V., Ivanov A.V., Malovik V.V., Martynov V.V., Panov V.S. Some results of studying structure of uranium dioxide powders
Characteristic properties of macro- and microstructures of the initial uranium dioxide powders have been considered. Suppositions of the mechanisms of different-origin powder behavior in pelletizing are made. The experimental data reflecting their effect on the quality of fuel pellets that is estimated according to the update techniques are given. Electron microscopy, helium picnometry, etc. were used to investigate the powder structure. The results presented here give evidence of disadvantages of "wet" techniques of initial UO₂ powder production using ADU scheme, since hard agglomerates and conglomerates are formed, thus complicating the pelletizing processes. Attention is emphasized on the major trends of the investigations, which can result in understanding of the regularities of initial UO₂ powder structure formation, permitting us to control the process of their production and stabilize the properties of powders and pellets.
Key words: nuclear fuel, uranium dioxide, uranium protoxide-oxide, pellet, density, porosity, crystallite, agglomerate, conglomerate, surface morphology, ADU - ammonium diuronate.

Theory and processes of powder material forming and sintering

Shmorgun V.G., Trykov Yu.P., Slautin O.V., Metelkin V.V., Bogdanov A.I. Kinetics of diffusion processes in nickel-aluminum composition
The kinetics of diffusion processes has been studied along interlayer boundaries of three-layer composites aluminum (AD1) + nickel (NP1) + aluminum (AD1) produced by explosive welding followed by cold rolling. The phase composition of the diffusion zone was determined.
Key words: layered intermetallic composites, diffusion, intermetallic layers, intermetallic phases, explosive welding.

Stolin A.M., Bazhin P.M., Pugachyov D.V. Rheological behavior of powdered charge materials during cold one-axle compression
A study of the compacting process kinetics for two widespread charging mixtures: Ti-B and Ti-C-Ni has been carried out. They are used within certain relations to produce synthetic cemented-carbide tool materials. Based on the experiments, the rheological properties of the cited powder system have been determined.
Key words: powder materials, rheology, deformation, one-axle compression, compaction.

Khramtsov V.D. On dispersed powder particle packing density
Design equations are proposed to determine density of compacting particles of two and three fractions of metal powders with the mean particle diameters ratio >10. The equations can forecast correctly the mix particle density and optimal ratios of their quantities and ensure the maximum density as a function of individual compacting densities and quantities of powders. The specific density after bumping-down is used as the value characterizing the particle packing density. Experimental check of the regularities has been carried out with the mixtures of three pairs of different powders, confirming the correctness of the equations obtained.
Key words: powders, particle packing density, particle size, density after bumping-down.

Levinsky Yu.V. Behavior of closed pores at the final sintering stage
A closed pore in crystalline and amorphous bodies is shown to contain always gas the pressure of which should be taken into account in calculating the pore size change rate. The systems of differential equations describing the pore size change kinetics and gas pressure in a pore have been proposed for two mechanisms of closed pore behavior in compact bodies. An analysis of pore behavior has been carried out both for the common case at commensurable values of surface tension forces, gas pressure, and external pressure and for various particular cases. Characteristic properties of pore behavior were found in the infinite space and in a finite body, at low and fast gas diffusion in solid bodies, in filling pores with monoatomic and diatomic gas as well as pore ensemble. Causes were analyzed and methods were proposed to calculate article swelling at the final sintering stage.
Key words: gas filled pores, diffusion of vacancies, viscous flow, theory of pore behavior.

High-melting-point, ceramic, and composite materials

Panov V.S., Shugaev V.A., Goldberg M.A. On possibility of Ni3Al utilization as binding material for hard alloys
The effect of holding time on limiting wetting angle ( ) of tungsten and titanium carbides by Ni₃Al intermetallic compound melt has been studied. Equilibrium value is shown to be varied from 38 degrees to 0. The WC solubility in Ni₃Al intermetallic compound is found to be 3-4 % at t = 1500 °С. Differential thermal analysis determined the temperature of the appearance of liquid phase in the WC-Ni₃Al system, being by 20-25 °С lower than for pure Ni₃Al. It has been found that WC-Ni₃Al alloys consist of two phases: first one on the basis of WC and second one on the basis of solid solution of tungsten carbide in Ni₃Al. The work of adhesion that testifies to the dominance of the chemical interaction in the system under consideration has been calculated.
Key words: carbide, intermetallic compound, melt, wettability, temperature, solubility, microstructure, contact zone, analysis, phase, X-ray photogram.

Chronicle

75th anniversary of Vladimir Nikitovich Antsiferov
Yury Romanovich Kolobov is 60 years old