Powder Metallurgy and Metal Ceramics (v.49, #11-12)

The interaction of iron-based powders with different phase compositions with model biological media is examined in experiments in vitro. The powders are synthesized from iron oxalates over a range from 450 to 830°C in a carbon-containing atmosphere and from citrates at 390 and 450°C with prolonged holding in a protective hydrogen atmosphere. The phase composition of the powders is determined using a DRON 3.0 x-ray diffractometer in Co-K α radiation. Human blood plasma is used as a biological medium and distilled water and a 0.9% NaCl solution as inorganic media. It is shown that different processes occur in blood plasma and inorganic media: corrosion in water media and interaction between iron and proteins to form iron–protein complexes in plasma-containing media. The dissolution rate of the powders in blood plasma depends on their α-iron content: the higher the latter, the more active the interaction of the powder with plasma proteins such as ferritin and transferrin, basic components of γ-globulin fraction. The powders synthesized by the decomposition–reduction of citrates at 450 and 390°C with prolonged holding in a protective hydrogen atmosphere interact with model solutions of digestive juice far more intensely, which makes them promising for the development of iron-containing food supplements.
Keywords: iron powders; blood plasma; digestive juice; proteins

Effect of high-voltage discharge on the particle size of hard alloy powders by O. N. Sizonenko; G. A. Baglyuk; A. I. Raichenko; G. P. Bogatyreva; N. A. Oleinik; É. I. Taftai; E. V. Lipyan; A. S. Torpakov (630-636).
The effect of high-voltage discharge treatment of Fe–20% TiC and VK6–1% ASUD75 diamond powder mixtures on their particle size and morphology is examined. It is shown that high-voltage discharge treatment in a powder suspension permits substantial refinement in the particle size and increase in the shape factor and specific surface area. A near-linear dependence is established between the total treatment energy and powder particle size. It is shown that hydrocarbon liquid is much more efficient than water as a working medium.
Keywords: powder; electric discharge; particle size; grinding; suspension

Simulation of the compaction dynamics of Cu + Al2O3 powder mixture under impulse hot pressing by M. S. Kovalchenko; T. P. Hrebenok; L. F. Ochkas (637-646).
The compaction dynamics of Cu + Al2O3 powder mixture under impulse hot pressing is simulated using a third-order dynamic system. The computer simulation has established the time dependence of the force induced by mechanical interaction between the impact machine and a heated porous blank, time variation in density, and root-mean-square strain rates and stresses in the matrix that forms the porous body. The phase trajectory of dynamic system from the beginning of compaction to the elastic recoil of the hammer block characterizes impact dynamics. The mechanical-thermal effect induced by bulk viscous flow and manifested itself as an increase in temperature of the porous body is determined. It is established that the shear viscosity of the porous body matrix shows a stronger dependence upon the initial impact velocity in comparison with the heating temperature. The activation energy of the matrix viscous flow is equal to 0.266 eV.
Keywords: simulation; compaction dynamics; porous body; copper; alumina; impulse hot pressing

Service properties of Cu–Sn–CuWO4–MoS2 composite and micromechanical characteristics of its friction surface by A. G. Kostornov; O. I. Fushchich; V. F. Gorban; T. M. Chevychelova; M. V. Karpets; A. Yu. Koval (647-653).
The paper examines the tribotechnical characteristics of the Cu–Sn–CuWO4–MoS2 antifriction composite during lubricated and dry friction at sliding speeds 0.5, 1, and 1.5 m/sec. X-ray diffraction of the material and its friction surfaces is conducted and their micromechanical characteristics are determined. The mechanism whereby the composite antifriction material attains the optimal tribotechnical characteristics is explained. It is established that the friction coefficient and wear rate of the composite depend, under varying friction parameters, on changes in the composition, structure, and micromechanical characteristics of the friction surface.
Keywords: composite antifriction material; friction coefficient; wear; wear resistance; serviceability; sliding speed; pressure; temperature; structure; micromechanical characteristics; x-ray diffraction; mechanism

Production of boron-containing powder steels using master alloys and boron carbide by G. A. Baglyuk; S. G. Napara-Volgina; L. N. Orlova; A. D. Kostenko; V. K. Kud (654-659).
The properties of boron-containing structural powder steels produced using master alloys and boron carbide are examined. It is established that sintered and thermally treated materials produced with master alloys show better mechanical properties than those made with the use of boron carbide. The boron content of structural powder steels that promotes the optimum combination of properties with the use of master alloys with different compositions is about 1.2%.
Keywords: powder steel; master alloy; boron carbide

Properties of intermetallic Ni–Al coatings deposited by high-velocity air–fuel spraying by Yu. I. Evdokimenko; V. M. Kisel; S. V. Buchakov; A. A. Rogozinskaya; D. Z. Yurchenko; R. V. Litvin (660-666).
The formation of intermetallic Ni–Al coatings by high-velocity air–fuel (HVAF) spraying is considered. The energy states of particles are calculated to determine the optimum grain-size composition of NiAl and Ni3Al powders. The properties of HVAF coatings from commercial PN85Yu15 and PTYu5N powders and test NAS powder deposited on steel, copper, and aluminum substrates are analyzed. The phase composition and structure of the coatings are provided. The properties of the coatings (porosity less than 1.5%, adhesion with steel substrate 44–57 MPa) are as good as those of the coatings produced with other thermal-spraying methods. The microstructure of the coatings is mainly formed by solid particles and partially by fine molten particles.
Keywords: thermal-sprayed coatings; high-velocity air–fuel spraying; intermetallides; nickel aluminides; structure; porosity; adhesion strength

Mechanical properties of spark-deposited restoration coatings by S. M. Kirilenko; O. V. Paustovskii; M. P. Berezhnitska (667-669).
The hardness, wear resistance, and internal stresses of spark-deposited iron-based coatings are determined. The slower deposition at greater spark discharge energy and the formation of plastic austenite promote the relaxation of internal stresses in the coating and increase its thickness.
Keywords: spark-deposited coatings; internal stresses; hardness; wear resistance

Production and properties of AlN–BN composite by G. N. Makarenko; L. A. Krushinskaya; V. B. Fedorus; T. V. Dubovik; A. V. Kotko; M. G. Andreeva; I. V. Uvarova (670-674).
The nitridation of an AlB2 precursor in a controlled nitrogen flow is examined with the aim of obtaining AlN–BN composite powders. It is shown that superfine powders with uniformly distributed AlN and BN phases and AlB12 admixture form over the temperature range 1000–1400°C. The powders do not require further grinding. The morphology and particle size of the powders and the microstructure and properties of hot-pressed samples are studied. The developed material exhibits better mechanical properties (as compared with known ABN composites): in particular, Rbm = 235 MPa and HV = 14.2 ± 1.3 GPa. The high bending strength and hardness are due to the finegrained structure of the samples and the strengthening effect of superfine (≤1 μm) inclusions of aluminum dodecaboride.
Keywords: aluminum nitride; boron nitride; aluminum boride; precursor; nitridation; particle morphology; microstructure; properties

Tool ceramics based on Al2O3–ZrO2–TiCN composite by Ya. G. Dyatlova; S. V. Agafonov; S. Yu. Boikov; S. S. Ordanyan; V. I. Rumyantsev (675-681).
Oxide composite Al2O3–ZrO2(Y2O3) powders containing 50 and 70 vol.% Al2O3, are deposited from salt solutions. The surface area of the deposited powders exceeds 75 m2/g. It is established that the α-Al2O3 and t-ZrO2(Y2O3) matrix has an effect on stepwise crystallization of α-Al2O3 and the powder production history on the sinterability of oxide composites. Ceramics based on Al2O3–ZrO2(Y2O3) composite powder containing 20 vol.% titanium carbonitride are hot pressed to be used as a cutting tool. The microstructure and mechanical properties of the ceramics are analyzed. The best mechanical properties are shown by ceramic samples sintered at 1550°C at 35 MPa: bending strength 950 MPa, fracture toughness 10.1 MPa ⋅ m1/2, and hardness 18.0 GPa. The performance and lifetime of cutting tools based on these ceramics are tested according to GOST 26613–85.
Keywords: Al2O3–ZrO2 system; titanium carbonitride; composite nanostructured materials; mechanical properties; cutting ceramics

Constitution of ZrCo–ZrIr alloys by O. L. Semenova; Yu. V. Kudryavtsev; V. M. Petyukh; A. V. Samelyuk (682-689).
A physicochemical analysis is used to examine the constitution of ZrCo–ZrNi alloys for the first time. The equiatomic ZrCo and ZrIr phases are found to form a continuous series of solid solutions over a range from the subsolidus temperature to the starting temperature of martensite transformation in ZrIr. The substitution of Co for Ir stabilizes the high-temperature ZrIr phase with a CsCl type structure. The extrapolation of linear temperature dependence of cobalt content shows that the hightemperature phase is stable at room temperature in the alloy containing about 15 at.% Co.
Keywords: zirconium; iridium; cobalt; phase diagram; martensitic transformation

Thermodynamic properties of holmium silicides HoSi1−x , Ho5Si4, AND Ho5Si3 by L. V. Goncharuk; V. R. Sidorko; Yu. I. Buyanov (690-694).
The Gibbs free energy, enthalpy, and entropy of holmium silicides HoSi1−x (HoSi0.98), Ho5Si4, and Ho5Si3 formed from solid components are determined by measuring electromotive forces over a range from 760 to 970 K. Holmium silicide Ho5Si3, which is the most refractory compound in the Ho–Si system, possesses the maximum thermodynamic stability. The high-temperature thermodynamic properties of formation of holmium silicides are determined for the first time.
Keywords: thermodynamic properties; Gibbs free energy; enthalpy; entropy of formation; holmium; silicon

The formation and decomposition of LaNi5H6, TiFeH2, Ti2NiH, TiNiH2, Ti2CuH2.7, TiCuH, Ti3AlH3, Mg2NiH4, Mg2CuH3, and ZrMn2.8H4 intermetallic hydrides are thermodynamically analyzed in identical conditions. These reactions are competitive and the interface between them is determined by boundary composition $ {{ ext{A}}_x}{{ ext{B}}_y}{{ ext{H}}_{{n_{ ext{b}}}}} $ . For LaNi5, TiFe, Mg2Ni, and ZrMn2.8, intermetallides, ranges of stable hydrogenation are equal to 17, 27, 5, and 17% of the maximum hydrogen capacity, and the others are ranges of metastable hydrides, over which decomposition reactions are limited kinetically. The improvement in kinetics of intermetallide hydrogenation prevents the decomposition of intermetallic hydrides. This is promoted by mechanical or catalytic activation of hydrogenation and by the use of heat-conducting nonvolatile metal matrix composites based on intermetallides.
Keywords: intermetallic hydride; hydrogenation; hydride decomposition

Anodic oxidation of SiC–TiB2–B4C composites in 3% NaCl solution by V. A. Shvets; V. A. Lavrenko; V. I. Subbotin; V. N. Talash; L. I. Kuznetsova (702-706).
Polarization curves and Auger spectroscopy are used to study the kinetics, formation mechanism, and layer-by-layer phase composition of oxide films resulting from the anodic oxidation of SiC–TiB2–B4C ceramics containing 10 wt.% and 40 wt.% TiB2 in 3% NaCl solution. It is shown that a two-layer oxide film forms in the former case (β-Ti2O3 is the lower layer and TiO2 the upper one) and a three-layer film forms in the latter case (nonstoichiometric β-TiO is the upper and lower layers and β-Ti2O3 the intermediate one). All ceramic samples, especially those with 10 wt.% TiB2, have high corrosion resistance.
Keywords: ceramics; silicon carbide; titanium boride; boron carbide; anodic oxidation; titanium oxides; polarization curves; Auger spectroscopy

The polarization dependences are recorded and the conditions of Ni–Co powder formation in amino-chloride electrolyte are found for different proportions of Ni2+/Co2+. Energy-dispersive spectral analysis (EDSA) is used to obtain data on the morphology and elemental composition of Ni–Co alloy powders depending on the Ni2+ and Co2+ ratio in the solution and the type and parameters of applied (controlled potential) current mode (stationary and impulse). It is found out that the increase of the Ni2+/Co2+ ratio in the solution results in the formation of finer powders as well as in higher nickel content of the powder, up to 64%. The application of impulse mode strongly increases both the dispersion (average size of the particles about 3–5 μm) and the powder homogeneity, which leads to lower oxide content of Ni–Co powders (below 2%). The increase in the impulse frequency to 1000 Hz, other conditions being equal, decreases the formation of dendrites and the susceptibility of powder particles to agglomeration.
Keywords: polarization curves; metal powders; Co; Ni; Ni–Co alloys; pulse electrolysis; morphology

The corrosion behavior of Al–Si–Bi (to 0.5 wt.% Bi) and Al–Si–Sb (to 0.5 wt.% Sb) ternary alloys is studied with polarization curves and scanning electron microscopy in 3% NaCl solution. The current density decreases with doping content to 0.05 wt.% and, thus, the corrosion rate slows down. With greater contents of antimony and bismuth, the current density of initial passivation increases and the active range on potentiodynamic curves reduces. This is indicative of lower corrosion resistance of the alloys.
Keywords: bismuth; antimony; silicon; aluminum; pitting corrosion; corrosion resistance; aluminum alloys; silumin

An extensive scanning electron microscopy and image analysis is carried out on Alumina and Zirconia Dispersed Alumina (ZDA) ceramic composites containing controlled amounts of tetragonal, monoclinic, and cubic zirconia phases. ZDA powders are prepared through a partial chemical route and sintered at 1600°C for 2 h in air. Zirconia nanoparticles reduce alumina matrix grain size by more than six times. Intricate relationships are revealed between zirconia allotropes and different microstructural parameters such as matrix grain size and its distribution, abnormal grain growth, zirconia particle size distribution, pore size, fracture mode, interparticle distance, etc.
Keywords: alumina dispersed zirconia composites; microstructural evaluation; particles

Sintering of powders without a circulating gas environment (review) by L. A. Sosnovskii; G. A. Baglyuk; I. G. Slys (730-736).
The paper summarizes and analyzes the known literature and data obtained by the authors on the development, use, and evolution of methods for nonoxidation sintering and chemical/thermal treatment of powders without protective gas environments. The efficiency of the method, including that for sintering of materials with high affinity to oxygen, is shown.
Keywords: sintering; powder; container; melt seal; filler; getter

Modeling the sintering of powder parts by M. V. Zagirnyak; V. P. Lyashenko; T. A. Grigorova; D. Miljavec (737-741).
The powder sintering process is modeled. A mathematical model and a system to control the temperature field in the sintering process are proposed. Soft-magnetic iron-based samples produced using the proposed control system are tested. The mechanical properties and structure of the material are analyzed to show that the plasticizer is uniformly distributed over the grain surface.
Keywords: mathematical model; algorithm; control system; structure; x-ray spectrum analysis; softmagnetic material; hysteresis