Powder Metallurgy and Metal Ceramics (v.48, #9-10)

The paper describes the formation kinetics of tribosynthesis phases in the friction area under impulsive thermal loading. The nature of structural changes and their interrelation with the tribotechnical properties of the friction pair are established.
Keywords: kinetics; tribosynthesis phases; friction contact; impulsive thermal friction; tribotechnical properties

Study of Al–Cu–Fe–Ti–Cr–Si powders for thermal spraying produced by mechanochemical synthesis and subsequent annealing by A. L. Borisova; L. I. Adeeva; A. Yu. Tunik; M. V. Karpets; V. L. Rupchev; A. N. Burlachenko (514-521).
The paper examines the phase transformations of composite powders based on Al63Cu25Fe12 that contain alloying elements (Ti, Cr, Si in the ratio AlCuFe : TiCrSi = 75 : 25). The powders are produced by mechanochemical synthesis and subsequent thermal treatment. Amorphous and crystalline powder mixtures form during synthesis; their annealing results in multiphase structures consisting of α, β1, and β2 phases. High-temperature x-ray diffraction has revealed an α-phase between 700 and 900°C. The new α-phase should be regarded as a 1/1 approximant of the nonequilibrium quasicrystalline phase. The maximum content of the approximant phase (68 wt.%) is observed after five-hour synthesis and subsequent annealing (T = 700°C, τ = 2 h) of pressed powders, microhardness of the particles reaching 8900 MPa.
Keywords: Al–Cu–Fe–Ti–Cr–Si system; powders; mechanochemical synthesis; structure; crystal lattice; phase transformations; amorphous; approximant; and quasicrystalline phases; hightemperature x-ray diffraction; thermal treatment

Tribotechnical characteristics of detonation coatings from mechanochemically synthesized Ti–Al–B powders by V. E. Oliker; V. L. Sirovatka; T. Ya. Gridasova; E. F. Grechishkin; A. D. Kostenko (522-528).
The tribotechnical characteristics of Ti–Al–B, Ti–Al–B–O, and Ti–Al–B–N detonation coatings and AL153 and KKhN-35 coatings under dry friction against different materials are compared. It is established that nitrides and oxides present in the coatings improve the friction characteristics. It is found out that friction pairs containing similar metals have the highest seizure capability. The coating whose structure represents an intermetallic matrix with inclusions of solid phases as titanium borides and oxides has the best characteristics.
Keywords: detonation coating; dry friction; intermetallic matrix

Wear resistance of spark-deposited TiN, TiB2, and Mo coatings on 30KhGSA steel after exposure to focused solar radiation by O. V. Paustovskii; G. O. Frolov; O. G. Molyar; V. I. Novikova; N. M. Mordovets; V. E. Shelud’ko; V. S. Tsyganenko; M. V. Lityuga; L. P. Isaeva; O. D. Kostenko (529-532).
The use of focused solar radiation to improve the mechanical properties of spark-deposited TiN, TiB2, and Mo coatings is studied. It is shown that the tribotechnical characteristics of sparkdeposited coatings improve after exposure to focused solar radiation over steel coatings after thermal treatment. Solar treatment of 30KhGSA steel leads to its strengthening—hardening with fine-grained annealed martensite being formed.
Keywords: alloying; current; solar treatment; coating; hardness; layer

Intermetallic TiAl and NiAl powders are synthesized by self-propagating high-temperature synthesis (SHS) involving a reduction stage. The effect of charge composition, stoichiometric ratio, and additives on the particle size, morphology, and phase composition of the resulting powders is examined. Addition of NaCl and excess Mg is found to suppress crystallization. In the presence of heat-generating additives, such as Mg(ClO4)2 and CaO2, the synthesized powders have particles smaller than 3 μm. The effect of Al content of the starting mixture on the morphology and phase composition of NiAl is studied.
Keywords: self-propagating high-temperature synthesis; combustion; intermetallics; powders; hightemperature structural materials

The paper examines the sintering kinetics of porous strips based on binary mixtures of ultrafine nickel, copper, and cobalt powders at 400–800°C under 5–20 MPa for 5–30 min. Concentration and kinetic dependences of shrinkage on sintering parameters are analyzed.
Keywords: ultrafine powders; rolled strips; sintering; temperature; pressure; holding time; shrinkage; strength

The paper studies the structure and mechanical properties of Kh12 and R2AM5F2NYu tool steels and ZChKh25 cast iron produced by gas spray forming. It is shown that rapid solidification during spray forming changes not only the structural type but also the class of materials and substantially improves deformability and mechanical properties. Billets from wear-resistant cast iron formed by spraying can be deformed by hot forging, stamping, and rolling with strain to 30%.
Keywords: tool steel; spray forming; solidification; crystallization; structurization; cooling rate; thermal treatment

Epoxy composite materials (ECMs) combine unique adhesive strength, heat resistance, and wear and corrosion resistance and are the basis for producing body components, sliding bearings, and protective coatings. To obtain epoxy composite materials, ÉD-20 epoxy resin, polyethylene polyamine as a curing agent, modifiers, and superfine reinforcements are used. Methods to control the structure and properties of ECMs with different reinforcement contents are justified, and structurization mechanisms depending on the nature and morphology of the ingredients and their ratios in the system are established. The structure and properties of epoxy composite materials depending on the reinforcement content are analyzed. Predominant factors that influence the properties of low-, medium-, and high-reinforced epoxy composites are identified. Additional ultrasonic treatment of composites in the formation stage is shown to be effective and improve the strength of the system owing to its higher homogeneity per microvolume, better wetting, and more active interaction at the interface.
Keywords: properties; reinforcement content; structure; composite; epoxy binder; ultrafine particles; system

Dependence of the resistivity of hot-pressed Si3N4–ZrC composites on their composition by E. V. Kirilenko; A. I. Derii; V. Ya. Petrovskii (560-568).
The paper examines the microstructure, phase composition, and resistivity of Si3N4-based composites depending on ZrC concentration and isothermal holding temperature. It is established that ZrCxNy forms in the composites during hot pressing. Its amount is determined only by isothermal holding temperature. It is shown that the resistivity and porosity of the composites depend not so much on the rate of chemical reactions as on the agglomeration of the starting powders when mixed. Addition of 10 to 20 vol.% zirconium carbide substantially changes the aggregation–disaggregation ratio. The reproducible resistivity of 0.5–10 Ω ∙ cm is reached. Thus these materials can be used as a resistive layer of small-size converters to perform under intensive heat exchange.
Keywords: silicon nitride; zirconium carbide; zirconium carbonitride; resistive composite; phase composition; resistivity

Effect of hot-pressing temperature on the phase formation and properties of boron carbonitride composite by O. N. Grigor’ev; N. D. Bega; T. V. Dubovik; O. D. Shcherbina; V. I. Subbotin; É. V. Prilutskii; V. A. Kotenko; A. A. Rogozinskaya; I. L. Berezhinskii; N. I. Siman; V. V. Lychko (569-577).
The dependence of the phase composition and properties of a boron carbonitride (BCN) composite on hot-pressing temperature is studied. It is established that the composite forms with the synthesis of new reinforcing phases in reaction sintering under pressure. The optimum conditions to obtain the BCN composite are determined. The BCN composite has high thermal strength, oxidation resistance, and electrical insulating properties.
Keywords: boron carbonitride; molybdenum silicide; glass phase; hot pressing; phase formation; composite; properties

Thermodynamic properties of holmium bismuthide by R. V. Antonchenko; L. V. Goncharuk; V. R. Sidorko (578-581).
The Gibbs free energy, enthalpy, and entropy of formation of holmium bismuthide are determined by measuring electromotive forces between 673 and 873 K.
Keywords: thermodynamic properties; Gibbs energy of formation; enthalpy of formation; entropy of formation; holmium bismuthide

Thermodynamic properties of binary Si–Y (transition metal) alloys by V. S. Sudavtsova; N. V. Kotova (582-587).
The partial (for yttrium) mixing enthalpies (∆ m $$ {overline H_Y} $$ ) of Si–Y molten alloys are determined using high-temperature isoperibolic calorimetry at 1770 ± 5 K for 0 < x y < 0.2. The integral mixing enthalpies (∆ m H) of Si–Y melts are calculated from these data. The formation of these molten alloys is accompanied by large exothermic heat effects. The generalized values of ∆ m H for molten Si–Y alloys are based on our and literary data. The activities of the melt components are calculated from liquidus coordinates of the Si–Y phase diagram. The values are characterized by very large negative deviations from the Raoult law. Correlation is established between the extremum of the integral mixing enthalpy for melts of silicon with d-metals and electronegativity differences and atomic radii of the alloy components.
Keywords: high-temperature isoperibolic calorimetry; enthalpies of mixing and formation; binary systems; melts; yttrium; silicon; d-metals

The thermodynamic potentials of binary TiB2–SiC, B4C–SiC, and B4C–TiB2 systems are constructed with the pseudopotential method. The energy of thermal oscillations is calculated using Einstein's model and the energy of interaction between atomic planes. The mixing energy of the systems is calculated to confirm that the eutectic is formed. The minimum thermodynamic potential is used to determine the eutectic temperatures and concentrations of the components.
Keywords: pseudopotential; thermodynamic potential; energy of mixing; energy of interaction; eutectic concentration and temperature; quasibinary system; atom oscillation frequency

Protective oxide layers formed during electrochemical oxidation of hafnium carbide by V. A. Lavrenko; V. N. Talash; M. Desmaison-Brut; Yu. B. Rudenko (595-599).
The composition of oxide nanofilm formed on the HfC anode under electrolysis of a 3% NaCl solution at potentials between – 0.20 and +1.90 V is studied using the potentiodynamic method of polarization curves and Auger electron spectroscopy and SEM methods. The film consists of the upper layer formed in polymolecular chemosorption of O2 and Cl2 gases followed by the HfO2 + C (1 : 1) layer. Two inner layers represent a 7 at.% O2 solid solution in HfC and a mixture of HfC0.7O0.3 and HfO (7 : 1). The oxide film 30–40 nm thick formed at potentials up to 1.35 V is protective and ensures very high corrosion resistance of HfC without any further polarization.
Keywords: hafnium carbide; chemosorption; anodic oxidation; formation of protective nanofilm; hafnium oxycarbide; hafnium oxides

The seizure of Ag, Cu, and Ni electrodes in low-voltage pulse discharges during coating of a copper plate is studied. It is established that nickel tends to seizure because of the high surface tension of its melts, which prevents the evacuation of the liquid metal from the anode surface, and also of its relatively low heat conductivity, which limits the heat removal from the support spots of the discharge channel into the electrode. This results in the smooth surface of the electrode and increases the contact area and contact temperature of the electrode couple, which enhances the probability of seizure.
Keywords: electrode seizure; pulse discharge; coating; electrical erosion

High-temperature oxidation of composite based on double titanium–chromium carbide by A. P. Umanskii; V. A. Lavrenko; S. S. Chuprov; V. P. Konoval (607-609).
The effect of a metallic binder and nickel coating on the high-temperature oxidation resistance of a composite material based on double titanium-chromium carbide is studied. It is shown that the introduction of a Fe–Cr binder decreases the rate of oxidation of the base material, but the maximum weight increment of the samples remains as it is in the initial TiCrC because of the oxidation of binder components. The nickel coating not only substantially decreases the oxidation rate of the composite components, but also shifts the thermal effects toward much higher temperatures. The oxidation occurs in two stages for compact samples, in three stages for the composite material, and in four stages for the composite material with nickel coating.
Keywords: composite material; double titanium–chromium carbide; high-temperature oxidation; nickel coating