Powder Metallurgy and Metal Ceramics (v.51, #1-2)

Composition and structure of functional groups on the surface of tungsten disilicide powder by A. D. Chirkin; V. O. Lavrenko; M. L. Malysheva; L. I. Kuznetsova (1-6).
X-ray photoelectron spectroscopy and infrared spectroscopy are used to establish that functional groups of three types form in air in the presence of water traces on the surface of WSi2 powder: silanol groups and residues of H2WO4 tungsten acid and H4[Si(W3O10)4] tungstate–silicate heteropolyacid (with the dominating role of silanol groups present on the surface in the greatest amount). It is shown that the surface properties of WSi2 are similar to those of SiO2 and SiC.
Keywords: tungsten disilicide; powder surface; functional groups; silanol groups; residues of H2WO4 and H4[Si(W3O10)4] acids

Interaction of carbonyl iron powders with different particle sizes with biological and inorganic media by N. V. Boshitska; Yu. I. Naida; I. V. Uvarova; A. Yu. Naida (7-12).
The dissolution of carbonyl iron powders with different particle sizes (with an average particle size of 1–3, 2–5, and 25–50 μm) in a model solution of gastric juice and human blood plasma is studied to evaluate their suitability as food supplements. The powders were ground and mixed using a mill developed and made at the Frantsevich Institute for Problems of Materials Science. The grinding efficiency is promoted by the interaction of particles with each other and with the working chamber. It is shown that iron powders interact most intensively with biological media containing organic acids that transform iron into a hydroxide, promoting its binding with proteins of blood plasma and pepsin to form easily assimilable complexes. The dissolution of iron powders in biological media depends on their particle size. The grinding of iron powders for 60 min practically doubles the intensity of their interaction with biological media (blood plasma and gastric juice model solution) and, therefore, promotes the assimilation of iron in the human body.
Keywords: powders; carbonyl iron; blood plasma; pepsin; interaction

Properties of composite magnetic abrasive powders with surfactants by V. V. Nepomnyashchii; K. A. Gogaev; S. M. Voloshchenko; T. V. Mosina; M. G. Askerov (13-16).
Magnetic abrasive powders produced by mechanical mixing of abrasives (electrocorundum, silicon and vanadium carbides) and iron powders in the presence of surfactants (oleic acid) and binding organics (epoxy resin) are proposed. The content of surfactants and binding organics does not exceed 8–10%. The dependence of the magnetic properties of composite powder on its abrasive content is studied. The effect of the type of abrasive on the cutting ability of the magnetic abrasive material and on the surface roughness is determined. The roughness (Ra) reached on steel 45 (HRC = 44–46) with the use of Fe–50% SiC abrasive is 0.08–0.12 μm.
Keywords: magnetic abrasive powders; roughness; abrasive; magnetic properties; cutting ability

Modern approaches to calculating the strength of green compacts by van der Waals forces (σVW) are reviewed. Respective components (σVW) are calculated and green tensile strength (σtl.av) is experimentally determined for test powders of metals (Al, Zn, Cu, Ni, and Mo) and one nonmetal (FeSi). Comparison of σtl.avVW ratios shows that σtl.av and σVW are of one order for the atomized zinc powder, and σVW is greater than σtl.av for the atomized copper powder, though σtl.av is greater than σVW by two to three orders for most powders with irregular shape of particles. This difference can be attributed to the effect of shape and mechanical interlocking or seizure of particles when compacted. To predict the green strength, it is necessary to take into account both the shape of particles (or relative apparent density of the powder) and the forming temperature.
Keywords: green strength; van der Waals forces; particle shape; powders; relative apparent density; forming temperature

The paper describes a new environmentally friendly technology involving plasma sputtering of conductive materials and dispersion of the resulting nanoparticles in various liquids as one-step production cycle. The physical and chemical characteristics of the prepared nanodispersions are presented, specifically for nanosilver dispersion in food glycerin. The schematic and design of a prototype setup with multiple nanodispersion modules for fabricating new nanoproduct, Silver Shield-1000, are shown. The advantages of the new technology and equipment are described.
Keywords: nanodispersion; nanosilver; colloidal dispersion; size distribution

A new approach to the formation of the mechanical properties of iron-based powder materials is proposed. The approach is based on model ideas on the structurization of bulk powder mixtures under compacting pressure. It is established that as the porosity increases (decreases) within the range 5–25 %, the structure of compacted powder mixtures (compacts) alternates between mesostructural and submesostructal states.
Keywords: sintered powder materials; iron; structure modeling; elastic aftereffect of compacts; meso- and submesostructure; elastic wave velocity

The relationship between deposition temperature, coating inhomogeneity, and temperature of cathode spots is studied. It is shown that the spark deposition of coatings proceeds in the area of cathode spots; therefore, the substrate temperature has an essential effect on the deposition process. A simple model is proposed to evaluate the relationship between the temperature of cathode spots and deposition temperature and coating inhomogeneity.
Keywords: electrospark deposition; cathode jets; cathode spots; substrate temperature

New structural unidirectional-fiber material by V. G. Borovik; O. N. Grigorev; V. N. Subbotin (49-55).
Structural basaltic materials are analyzed to establish the relationship of their structure to strength and fracture resistance. It is shown that their strength is determined by the size of initial crack-like defects, and fracture resistance by the amount and extent of weak boundaries that are perpendicular to the growing main crack. Samples of one-component unidirectional basalt fiber material of channel structure were produced by hot pressing. It is shown how temperature and time under pressure influence the structure and fracture behavior of the material.
Keywords: basalt; hot pressing; structural material; fibrous structure; bending strength; fracture resistance

Structural dispersion of powder titanium in the optimal conditions of dynamic hot pressing by Yu. N. Podrezov; V. A. Nazarenko; A. V. Laptev; A. I. Tolochin; Ya. I. Evich; N. I. Danilenko; O. M. Ivanova (56-63).
The effect of dynamic hot pressing temperature on the mechanical properties of powder titanium is studied. The best properties are demonstrated by titanium samples pressed at 910°C. Fine-grained structure with 2–5 μm grains forms under these conditions. This permits 25% increase in the strength of the material as compared with conventionally produced titanium.
Keywords: porosity; powder titanium; tensile strength; hot pressing; grain size; microstructure

Production and properties of oxidation-resistant spark coatings on titanium alloys by A. V. Paustovskii; Yu. G. Tkachenko; R. A. Alfintseva; D. Z. Yurchenko; V. F. Britun; L. P. Isaeva (64-70).
The paper examines the deposition of spark coatings from Ni–Cr–Al alloy, pressed and sintered in vacuum, on titanium alloys. The spark deposition parameters are optimized to produce coatings with a thickness to 30 μm, density not lower than 80%, and hardness about 8 GPa. It is shown that spark-deposited coatings on VT6 and VT22 alloys permit increase in their oxidation resistance by a factor of 1.5 to 2.5 during isothermal holding at 800°C. This increase is due to the formation of oxidation-resistant titanium phases on coatings, which prevent the diffusion of elements from air into the coating.
Keywords: titanium alloys; electrospark deposition; coating; electrode material; nickel; chromium; aluminum; oxidation resistance; phase composition

Formation of (Si–C)–Al ceramic composites in air by N. K. Davidchuk; N. F. Gadzyra (71-75).
The paper studies the formation of a (SiC–C)–Al ceramic composite during high-temperature heating. The optimum composition of the starting mixture and conditions for producing superhard ceramics are established. The microstructure of the sintered samples is examined.
Keywords: solid solution of carbon in β-SiC; aluminum; pressureless sintering; phase composition; microstructure; precipitation hardening; ceramic composite

The paper presents experimental results for high-speed thermal treatment of SiAlON ceramics using spark plasma sintering and gas-pressure combustion sintering. The temperature ranges that determine the density, phase composition, and microstructure in multicomponent SiAlON systems are established. Individual phases of the sintering process and the effect of constitution and basic properties of starting powders on the microstructure and phase composition of sintered SiAlON ceramics are analyzed.
Keywords: sialon ceramics; spark plasma sintering; combustion wave; self-propagating hightemperature synthesis

Electrical properties of mechanochemically activated cordierite ceramics by N. G. Djordjevic; N. Obradovic; S. Filipovic (83-86).
Three-component oxide mixtures were prepared containing MgO, Al 2 O 3 and SiO 2 in a 2 : 2 : 5 ratio with addition of 10% Bi 2 O 3. The mixtures were mechanically activated in a range from 5 to 240 min in a mill with ceramic balls, and sintered in the range 1173–1573 K. In order to determine the structure transformations, sintered products were analyzed by the XRD method. The goal of the research was to find the possible correlation between process parameters and functional properties of the cordierite-based ceramic materials. Quantitative measures of the functional sample properties, capacity (C c ) and electrical resistance (R ρ), as well as of dielectric loss (tgδ) were used. The results obtained prove that there is a correlation between mechanical activation and properties of cordierite ceramics.
Keywords: mechanical activation; electrical properties; cordierite ceramics

The Al2O3–HfO2–Gd2O3 phase diagram. I. Isothermal sections at 1250 AND 1650°C by S. M. Lakiza; Ya. S. Tishchenko; V. P. Red’ko; L. M. Lopato (87-92).
The isothermal sections of the Al2O3–HfO2–Gd2O3 phase diagram at 1250 and 1650°C are constructed for the first time and phase equilibria at these temperatures are established. No ternary compounds or appreciable solid solution regions based on components or binary compounds are found in the ternary system. Interaction in the system is determined by the most thermodynamically stable compound, HfO2, which equilibrates with all phases in the system. In the region with Gd2O3 content up to ~65%, the sections are similar, only width of the regions changes. This is connected with changes in the extension of M and F solid solutions in the HfO2–Gd2O3 binary bounding system. The presence of AL + F, GA + GH2, and G2A + F two-phase regions at the isothermal sections suggests that there are triangulating sections of the Al2O3–HfO2–Gd2O3 system in them. Since the F and GH2 phases are of variable composition, these sections can be qualified as conditionally quasibinary. In wide three-phase regions, like in the Al2O3–ZrO2–Gd2O3 system, ternary eutectic points are expected to exist.
Keywords: ceramics; hafnia; alumina; gadolinium oxide; interaction; isothermal section; phase diagram; eutectic materials

Thermodynamic and thermochemical characteristics of erbium silicides by V. R. Sidorko; N. P. Gorbachuk (93-101).
The Gibbs energy, enthalpy, and entropy of formation of erbium silicides ErSi2–b (ErSi1.67), ErSi, ErSi1–x (ErSi0.96), Er5Si4, and Er5Si3 are determined by measuring electromotive forces in the range 820–1050 K. The enthalpy of ErSi1.67, ErSi, and Er5Si3 in the wide temperature range is studied by drop calorimetry. The temperature dependences of the heat capacity, entropy, and reduced Gibbs energy of these compounds are derived from experimental data. The enthalpies and entropies of the polymorphic transformation β-ErSi2–b ↔ α-ErSi2–b and the melting enthalpy and entropy of ErSi2–b, ErSi, and Er5Si3 silicides are also established.
Keywords: Gibbs energy of formation; enthalpy of formation; entropy of formation; heat capacity; enthalpy and entropy; reduced Gibbs energy; erbium silicides

High-temperature (to 1600°C) oxidation of ZrB2–MoSi2 ceramics in air by V. O. Lavrenko; A. D. Panasyuk; O. M. Grigorev; O. V. Koroteev; V. A. Kotenko (102-107).
Thermal gravimetry and differential thermal analysis are used to study nonisothermal hightemperature oxidation of 56 wt.% ZrB2–44 wt.% MoSi2 and 86 wt.% ZrB2–14 wt.% MoSi2 ceramics in air up to 1600 °C. Oxide layers that form on samples at different oxidation stages are studied using AES, EDX, and SEM analyses. It is concluded that the ZrB2–MoSi2 ceramics exhibit exceptionally high oxidation resistance.
Keywords: ceramics; zirconium diboride; molybdenum disilicide; high-temperature oxidation; layerby- layer analysis of oxide layers

The paper analyzes the potential yield of reaction products or the degree of conversion in a gas– solid system. Dependences of the degree of conversion for the solid phase on gas composition for various types of reactions are presented. They are used to assess the reactivity of the system. The data may be used in planning and implementation of respective processes.
Keywords: analysis; gas; reagent; degree of conversion; chemical reaction

Structural and phase transformations on spark-laser coatings under fretting corrosion in air by V. M. Panashenko; I. A. Podchernyaeva; A. I. Dukhota; A. D. Panasyuk (112-120).
The structure and phase transformations on the surface of a ZrB2-based combined laser–spark coating on titanium alloy are studied. The transformations are induced by triboprocesses under fretting corrosion in air. It is shown that the surface transformations result from a combination of three mechanisms: plastic deformation (surface texturing, fatigue, crack formation, brittle fracture); oxygen diffusion from the environment, chemical reactions of tribooxidation, diffusion of substrate elements (Al) toward the wear surface; and removal of particles from the surface. Two-phase nanostructured eutectic is found on the wear surface of the combined coating.
Keywords: laser–spark coating; zirconium diboride; fretting; tribofilm; structure and phase transformations

Crystalline titanium phosphate α-Ti(HPO4)2 ⋅ H2O (α-TiP) has been prepared by reaction between phosphoric acid solution and titanium chloride in the temperature range 60–80 °C. The solid obtained has been treated, in solid state with different concentrations of either cobalt or nickel. The pure and derivative materials are characterised using X-ray powder diffraction, Fourier transform IR, differential thermal analysis, and nitrogen adsorption. Due to their higher degree of hydration, the cobalt atoms are more sorbed by (α-TiP), where they enter into the cavities (containing the water molecules) between the layers of titanium phosphate. It is found that this process can induce small expanding of the interlayer spacing in the C direction and losing the crystallinity in the other directions. For the nickel, after sorption of more than 20%, an atomic layer may be formed preventing (α-TiP) from accommodating any more nickel ions in its framework, this is displayed by the appearance of diffraction peaks related to unsorbed nickel. The DTA curves indicate that more crystalline α-TiP materials have higher transition temperature. The nitrogen adsorption isotherms give an indication that when the cobalt atoms are sorbed by α-TiP, the latter is transformed from microporous to mesoporous material while it keeps its pore uniformity in the case of nickel.
Keywords: α titanium phosphate; cobalt; nickel; atoms; sorption; DTA curves; isotherms; texture