Powder Metallurgy and Metal Ceramics (v.50, #3-4)

The papers that describe basic stages in the production of continuous basalt fibers are reviewed. The effect of rheological and crystallization properties of basalt melts on the production of fibers is considered. It is established that the higher the ratio of viscosity to surface tension η/σ, the more stable the formation of fibers. The viscosity and crystallizability of the melt determine the fiber-forming temperature range. Features of the process for producing fibers from mineral basalt raw material are described. It is established that the temperature range for the formation of basalt fibers is narrower than that for glass fibers. This is due to the more pronounced temperature dependence of viscosity and higher crystallizability of basalt fibers. The high wettability and high infrared absorptance of basalt melts are factors that influence the effectiveness of the formation process. Therefore, the continuous basalt fiber production process should be optimized.
Keywords: fiber production process; basalt melt; rheological properties; crystallization

Mode I and mode II stress intensity factors (SIFs) are determined for a material with parallel pore channels of Y-shaped cross-section with centers at nodes of a regular hexagonal grid and arms aligned with the sides of hexagons. Calculations are performed for a unit cell that includes halves of two adjacent pore channels with an arbitrary length ratio of the arms. The finite-element method is used. It is shown that the SIFs for an equal-arm Y-shaped pore channel depend on the fiber cross-sectional radius of curvature. The range of lengths of periodic equal-arm starlike cracks in which they can be regarded as noninteracting is identified.
Keywords: unidirectional fibers; pore channel; Y-shaped crack; starlike crack; stress intensity factor

316L stainless steel parts are manufactured via selective laser melting. The investigation into the main characteristics and metallurgical mechanisms of selective laser melting process are highlighted in this work. The morphologies, microstructures and elemental compositions of as received scan tracks and samples are detected through optical microscope, SEM and energy dispersive X-ray spectroscopy respectively. The morphology of melted track exhibits scaly figures from top view, which is similar to welding process. The central zone of melted track shows a cellular microstructure while the edge zone of molten pool represents a columnar structure, which is caused by the heat transfer process. The surface morphology of SLM part in low magnification can show multi-lined feature, and the surface morphology in high magnification can reflect the solidification and crystallization process. Moreover, a little amount of oxide and splash with balling effect can also be found on the SLM part surface. The microstructure of SLM part is extremely fine coupled with multiple crystal directions. The very fine crystal structure is caused by the extraordinarily rapid cooling and the multiple crystal directions are due to the variable heat transfer direction. The element distribution is homogeneous and no elemental aggregations can be found. The metallurgical mechanisms for the above characteristics are also addressed.
Keywords: selective laser melting; stainless steel; forming; microstructure

Change in pore structure of yttria-stabilized zirconia during sintering by S. V. Gabelkov; R. V. Tarasov; A. G. Mironova (151-156).
The behavior of coarse and fine pore channels and closed pores (pore space components) in temperature ranges of intensive (900–1150°C) and less active (1150–1400°C) sintering of a sample pressed from nanosized powder of tetragonal zirconia solid solution is examined. The change in the volume of the sample in the temperature range of intensive sintering is determined by approximately equal decrease in the volume of coarse and fine pore channels, which originate from channels between agglomerates and between aggregates in the powder agglomerates. Closed pores of the sample originating from closed pores of the powder make a minor contribution to the decrease in volume since they contain air. In the temperature range of less active sintering, all fine (200–300 nm) and coarse (0.8–1 μm) pore channels are broken and new closed pores are formed.
Keywords: nanosized powder; zirconia; pore space; pore channels; closed pores; sintering; activation energy

Field assisted sintering of nanocrystalline titanium nitride powder by V. G. Kolesnichenko; V. P. Popov; O. B. Zgalat-Lozinskii; L. A. Klochkov; T. F. Lobunets; A. I. Raichenko; A. V. Ragulya (157-166).
The effect of field assisted sintering (FAS) on the compaction of TiN ceramics is examined using a nanosized TiN powder. Microstructural evolution at different stages of FAS is evaluated using electron microscopy. Coarse spherical particles (1–5 μm) are found at 700°C. These particles apparently result from excessive heat release on interparticle contacts when an electrical current passes through agglomerates at certain stages. The specific surface area and pore size distribution in sintered samples are examined with static volumetric absorption. The compaction and microstructural evolution are discussed in terms of electric field effects.
Keywords: nanocrystalline powder; titanium nitride; field assisted sintering; microstructure; specific pore volume; microhardness

Control of the composition and structure of Fe–O nanoparticles during Fe3O4 electron beam evaporation by B. A. Movchan; Yu. A. Kurapov; G. G. Didikin; S. G. Litvin; S. M. Romanenko (167-172).
The paper examines the structure of porous Fe3O4 + NaCl condensates and analyzes the phase and chemical composition and sizes of Fe3O4 nanoparticles produced by electron beam evaporation and vacuum condensation. It is shown that Fe3O4 nanoparticles in a porous salt matrix are highly adsorptive to air oxygen. The adsorptivity decreases when iron concentration in the condensate increases. Thermogravimetric analysis is used to study the kinetics of variation in the weight of porous NaCl and Fe3O4 + NaCl condensates during heating to 650°C and cooling in air. The results are considered in terms of physical and chemical adsorption. Stabilized colloidal systems of magnetite nanoparticles are obtained. Photon correlation spectroscopy is used to determine their quantitative size distribution in an aqueous solution of surface active agents. The physical method for obtaining nanoparticles in electron beam vacuum setups is highly efficient and competitive with previous methods for synthesis of nanoparticles.
Keywords: electron beam evaporation; nanoparticles; magnetite; adsorption; oxygen

Electrodeposition of tertiary alumina/yttria/carbon nanotube (Al2O3/Y2O3/CNT) nanocomposite by using pulsed current has been studied in this investigation. Coating process has been performed on nickel sulphate bath and nanostructure of obtained compound layer is examined with high precision figure analysis of SEM nanographs. The effects of process variables, i.e., Y2O3 concentration, treatment time, frequency and duty cycle, have been experimentally studied. Statistical methods are used to achieve the minimum of corrosion rate and average size of nanoparticles. Finally the contribution percentage of different effective factors is revealed and confirmation run shows the validity of obtained results. Also it has been revealed that by changing the size of nanoparticles, corrosion properties of coatings will change significantly in the same trend. AFM and TEM analyses have confirmed smooth surface and average size of nanoparticles in the optimal coating.
Keywords: yttria; electrodeposition; tertiary nanocomposite coatings; corrosion; carbon nanotube

Dissolution of chromium carbide Cr3C2 in Kh17N2 steel during sintering by R. V. Yakovenko; V. A. Maslyuk; A. N. Gripachevskii; V. B. Deimontovich (182-188).
The effect of sintering temperature (900–1300°C) on the interaction of Cr3C2 with a Kh17N2 steel matrix is studied. It is shown that complex iron–chromium carbide of (Cr, Fe) x C y type forms during sintering. With increasing temperature, it undergoes a number of phase transformations. The following mechanism of Cr3C2 dissolution in the steel matrix is established: Cr3C2 → 900°C (Cr, Fe)2C → 1050°C (Cr, Fe)7C3 → 1200°C (Cr, Fe)23C6 → 1300°C (Cr, Fe)2C.
Keywords: chromium carbide; steel matrix; sintering; phase transformations; x-ray microanalysis

Effect of carbon content on the properties of sintered steels doped with manganese and copper by G. A. Baglyuk; L. A. Sosnovskii; V. I. Volfman (189-193).
The properties of sintered steels doped with manganese and copper and produced using copper- bearing ferromanganese master alloys are examined with respect to temperature and concentrations of the master alloy (3–10%) and graphite (0–1.0%) in the charge. It is shown that increase in the concentration of the master alloy and graphite leads to the relevant increase in steel strength. The hardness of steel with the minimum content of the master alloy (3%) becomes substantially higher when carbon is introduced and weakly depends on sintering temperature. If the concentration of the master alloy is higher (7 and 10%), the effect of sintering temperature on hardness noticeably increases, while the effect of graphite content substantially decreases. With increasing concentration of the master alloy, the hardness of the sintered steel becomes higher regardless of sintering temperature and graphite content of the charge.
Keywords: sintered steel doped with manganese and copper; master alloy; graphite; iron powder; ferromanganese; sintering

Effect of silicon-containing additives on the phase constitution and properties of boron carbonitride composites by O. N. Grigor’ev; T. V. Dubovik; N. D. Bega; O. D. Shcherbina; V. I. Subbotin; V. A. Kotenko; É. V. Prilutskii; A. A. Rogozinskaya; V. V. Lychko; I. L. Berezhinskii; L. M. Udovenko (194-201).
The phase constitution and properties of BNC composites (with SiC and SiO2 (quartz glass) additives) are studied as functions of hot pressing temperature. The developed BNC composites have higher mechanical strength and oxidation resistance than hot-pressed BNC without additives and retain high insulating properties, thermal and chemical resistance, and good machinability.
Keywords: boron carbonitride; silicon carbide; quartz glass; hot pressing; composite

Structure and phase formation in boron carbide and aluminum powder mixtures during hot pressing by Yu. G. Tkachenko; V. F. Britun; D. Z. Yurchenko; M. S. Kovalchenko; I. I. Timofeeva; L. P. Isaeva (202-211).
The paper examines the structure and phase formation during hot pressing of boron carbide powder mixtures containing 20–50 vol.% aluminum and analyzes the microhardness and fracture toughness of the hot-pressed samples. It is established that the particle size of the starting powder has an essential effect on the structure and mechanical properties of boron carbide composites. A matrix structure consisting of aluminum carboboride and borates and inclusions of boron carbide forms during hot pressing of mixtures containing coarse B4C powder. The microhardness of the matrix varies from 20 to 25 GPa and that of boron carbide grains from 42 to 44 GPa. Homogeneous fine- grained structure mainly consisting of aluminum nitride and borates forms in hot-pressed mixtures containing fine boron carbide. Its microhardness is 33–37 GPa and fracture toughness 5.4–5.7 MPa ⋅ m1/2.
Keywords: boron carbide; aluminum; hot pressing; phase composition; structure; mechanical properties

Activated sintering of refractory borides by G. L. Zhunkovskii; T. M. Evtushok; O. N. Grigor’ev; V. A. Kotenko; P. V. Mazur (212-216).
The interaction of titanium, zirconium, and tungsten borides with chromium is studied. It is shown that the process is induced by contact melting involving intensive wetting of borides with interaction products at temperatures much lower than the melting points of components. The temperature dependences of contact angles and the phase constitution of interaction products are analyzed. Chromium vapors that reduce the strength of chemical bonds in the lattice lead to a liquid eutectic phase with low contact angles to the surface of borides and promote the activated sintering of boride systems. It is demonstrated that low-porous (1–2%) borides can form at sintering temperatures lower than the temperature of secondary recrystallization. The dependence of bending and compressive strength on sintering temperature is examined. Conditions for producing low-porous fine-grained materials are determined.
Keywords: borides; chromium; eutectic; contact interaction; wetting; activated sintering

The Al–Cr–Fe phase diagram. II. Liquidus surface and phase equilibria for crystallization of 58–100 at.% Al alloys by V. G. Khoruzha; K. E. Kornienko; D. V. Pavlyuchkov; B. Grushko; T. Ya. Velikanova (217-229).
Data on the solidus surface of the Al–Cr–Fe system in the range 58–100 at.% Al and on the cast alloys examined with metallography, x-ray diffraction, and differential thermal and electron microprobe analyses are used to construct the liquidus surface of this system on the concentration triangle and study the processes that occur during crystallization of its alloys. This has permitted the construction of the Al–Cr–Fe melting diagram in the range 58–100 at.% Al. The liquidus surface includes primary crystallization fields of four ternary compounds, eight solid solutions based on binary phases, and a solid solution based on aluminum. There are fourteen four-phase invariant equilibria involving a liquid phase (three eutectic, two peritectic, and nine transition equilibria) and eight three-phase invariant equilibria involving a liquid phase.
Keywords: liquidus surface; crystallization; phase; melting diagram

Thermodynamics of interaction between refractory compounds and metal melts by V. P. Konoval; A. D. Panasyuk; V. A. Lavrenko (230-238).
Based on the thermodynamic assessment of equilibria in “refractory compound–metal melt” systems, the interaction in B4C–Al (Ni, Ni–Si, Ni–Mo) systems is predicted within the Van Laar theory at temperatures to 1800 K. It is established that interphase-active elements (nickel, titanium, vanadium, and chromium), being in a solid-solution state, do not show sufficient chemical activity or do not form new chemical compounds in interaction with refractory compounds (carbides, borides, and nitrides of IV–V group metals) unlike “refractory compound–liquid metal (Ni, Cr, Ti)” systems.
Keywords: metals (Ni, Cr, Ti); refractory compounds; interaction; chemical activity; Van Laar concept; thermodynamic equilibrium calculations

The enthalpy of Er5Ge3 is measured for the first time with drop calorimetry in the range 467–2335 K. The temperature dependences of enthalpy, heat capacity, entropy, and Gibbs free energy are obtained. The melting enthalpy and entropy of the compound are calculated.
Keywords: thermodynamics; enthalpy; heat capacity; entropy; Gibbs free energy

New grades of submicron and nanosized powders of cubic boron nitride by G. P. Bogatyreva; M. A. Marinich; G. A. Bazalii; G. K. Kozina (243-248).
A technique for producing new grades of submicron and nanosized powders of cubic boron nitride (cBN) is developed. It includes preliminary treatment of powders and their surface modification to control the hydrophilic–hydrophobic balance. Processes are developed for producing submicron and nanosized powders of cubic boron nitride that change their hydrophilic–hydrophobic balance. Thermal treatment in inert environments makes the surface of cBN powders hydrophobic and electrochemical treatment makes it hydrophilic. New grades of submicron and nanosized powders of cubic boron nitride are created. Hydrophobic KSM-F and KN-F powders are recommended for the production of polycrystalline materials and tools on their basis and hydrophilic KSM-É and KN-É powders for composite coatings, suspensions, and pastes.
Keywords: submicron and nanosized powders of cubic boron nitride (cBN); surface modification; thermal and electrochemical treatment