Powder Metallurgy and Metal Ceramics (v.53, #3-4)

Expansion on radomyselskii’s Ideas in the Development of Current Processes for Producing Structural Powder Parts by Yu. G. Dorofeev; G. A. Baglyuk; V. Yu. Dorofeev; A. V. Babets (129-138).
The basic scientific trends of studies conducted over many years under the leadership of I. D. Radomyselskii are considered. It is shown that most of them are still relevant. The main areas and prospects of expanding on these ideas today are presented.
Keywords: powder metallurgy; structural material; properties; sintered steel; technology

The effect of applied load on density–pressure dependence as well as density distribution under axial pressing of powders in closed dies is analyzed. The continuity hypothesis is used for the analysis. The notion of a representative element is introduced. It is established that the size of this element is related to the effective diameter of powder particles. The sensitivity of density–pressure dependence and density distribution to pressing conditions is explained. Some features of axial pressing with a rotating punch are pointed out. The personal contribution of I. D. Radomyselskii to the formulation and solution of basic problems of powder pressing theory is emphasized.
Keywords: pressing; compact; powders; density; pressure

The concept for producing wear-resistant structural powder materials for applications in space vacuum and atmospheres of planets in the solar system is described. The basic idea is to form nonequilibrium structures by introducing strengthening solid phases and unstable diselenides into the metal matrix to create dissipative structures responsible for the wear resistance of materials during sintering and dry friction.
Keywords: wear-resistant material; space applications; diselenide; dissipative structure

Automated Equipment for Producing Powder Parts by G. G. Serdyuk; I. D. Martyukhin (155-161).
The paper overviews activities guided by Radomyselskii to develop specialized powder metallurgy equipment: in particular, furnaces for producing iron powder, mechanical and hydraulic presses to make metal powder parts, as well as powder impact and hot forging presses. These developments inspired the design of industrial equipment for pressing powder products and automated hot forging lines.
Keywords: furnace equipment; specialized presses; automated lines; metal powder; powder products

The paper outlines Radomyselskii’s scientific contribution to the development of wear-resistant powder materials, corrosion-resistant tungsten-free hardmetals, and carbide steels. It is shown how the principle of structural heterogeneity proposed by I. D. Radomyselskii was implemented in the development of wear-resistant iron–white cast iron–chromium steel material and chromium carbide Cr3C2–Ni, Cr3C2–Ni–P, Cr3C2–Fe, and Cr3C2–stainless steel hardmetals. It is demonstrated that iron and steel powders, as well as high-carbon ferrochromium FKh800 powder, can be used successfully as starting materials to produce chromium carbide hardmetals and carbide steels, the scarcity and cost of chromium and nickel increasing. Data on the microstructure, mechanical and tribological properties, corrosion characteristics, and abrasive resistance are provided. The results of industrial tests and examples of the most effective use of tungsten-free hardmetals and wear-resistant powder materials containing simple and complex chromium carbides are presented.
Keywords: vertical section; chromium carbide; heterogeneity; hardmetal; carbide steel; ferrochrome; microstructure; wear resistance; corrosion resistance

The wear mechanism of powder iron–glass material is analyzed. The behavior of PS5GSh–PS5GSh and of PS5GSh–hardened steel 45 during friction in vacuum is studied. It is established that the glass inclusions and “white layer” formed on the friction surface influence the wear-resistance of the iron-glass material. It is noted that increased hardness leads the glass inclusions to form a near-surface framework, resisting the plastic deformation on the surface and inside the material. It is shown that the white inclusions have low friction adhesion and thus prevent seizure with steel. The “white layer” adheres strongly to the material. It acts as a solid lubricant and, along with the glass inclusions, increases the wear resistance. Extreme gross wear is accompanied by active growth and failure of the “white layer” as scales on dislocation slip planes located at an angle to the friction surface. The wear mechanism of the powder iron–glass materials under simultaneous contact of steel and glass is studied.
Keywords: iron-glass material; wear resistance; coefficient of friction; vacuum; structure; glass inclusions; microhardness

Electroforming of Powder Composite Materials by A. L. Maximenko; X. Wang; E. A. Olevsky; M. B. Shtern (176-179).
Electrochemical and electrophoretic deposition can be used for electroforming of powder-based composite billets with complex shape and microscopically nonuniform internal structure. Electrophoretic deposition of green bodies for near-net shaping of functionally graded ceramic composites and electroforming of heat sinks for electronic chips are considered as application examples. It is shown that electrophoretic forming allows shaping functionally graded billets to provide near-net-shape components after sintering. Heat sinks made from ceramic foam with copper electroplating provide a combination of high thermal conductivity with low thermal expansion coefficient, which is important for reliable fixation of the radiator on the chip surface.
Keywords: electroforming; powder; composite

The kinetics of nonisothermal pressure sintering of boron carbide powder mixed with 20 wt.% silicon carbide in the controlled heating mode is studied. The isothermal sintering kinetics of the mixture at temperature of 2240 K under applied pressures of 36.1, 49.6, 63.2, and 72.2 MPa was analyzed to determine the Laplace pressure. It is found that the kinetics is controlled by steady-state creep mechanism in the matrix forming the porous body, with the viscous flow rate being proportional to the square of stress. The relatively low value of the evaluated Laplace pressure (5.6 MPa) explains the difficulties in producing boron carbide composites with pressureless sintering. The current values of temperature and height of the samples during pressure sintering were used to determine the heating rate and the temperature derivatives of relative density, which enabled to describe the pressure sintering kinetics in the terms of the theory of bulk viscous flow of the porous bodies in a die. The evaluated activation energy of the intermediate and late stages of pressure sintering of the composite for different heating rates ranges from 670 to 710 kJ/mol. These values indicate that the sintering kinetics is controlled by dislocation climb mechanism. The structure and fracture behavior of the sintered samples are shown to depend on the heating rate. The higher the heating rate during B4C–20% SiC sintering, the more heterogeneous is the distribution of powder components and the larger the portion of transcrystalline fracture of sintered samples.
Keywords: kinetics; pressure sintering; powder mixture; boron carbide; silicon carbide; structure; fracture

In this paper, the results of numerical and experimental studies concerning the effect of mediumfrequency induction sintering of Fe–3 wt.% Cu powder metal (PM) compacts are discussed. Several sintering durations from 30 to 180 sec are studied. The mixed powders are compacted at 600 MPa and sintered by medium-frequency induction system (30–50 kHz frequency and 12 kW power). Magnetic and thermal analysis, mechanical properties, and densities of copper–iron PM compacts are presented.
Keywords: sintering; powder metal; iron; copper; medium-frequency induction sintering; magnetic analysis; thermal analysis

Production and Thermal Stability of Silver Nanoparticles in the Ag–O System by Yu. A. Kurapov; L. A. Krushinskaya; S. E. Litvin; S. M. Romanenko; Ya. A. Stelmakh; V. Ya. Markiev (199-204).
The paper examines the structure of porous Ag + NaCl condensates and analyzes the phase and chemical composition and sizes of Ag nanoparticles produced by electron-beam evaporation and vacuum condensation. It is shown that Ag nanoparticles are highly adsorptive to air oxygen in a porous salt matrix. Thermogravimetric analysis is used to study the kinetics of variation in the weight of porous NaCl and Ag + 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 silver nanoparticles are obtained. Photon correlation spectroscopy is employed to determine the size of nanoparticles in aqueous solutions with surfactant agents.
Keywords: electron-beam evaporation; nanoparticle; silver; adsorption; oxygen

Friction Wear of Modified Epoxy Composites by P. P. Savchuk; A. G. Kostornov; V. P. Kashitskii; O. L. Sadova (205-209).
Tribotechnical composites based on epoxy oligomers are used to benefit from special properties of epoxides showing high moldability, adhesion ability, and corrosion resistance and low shrinkage. Epoxy resin ED-20, polyethylene polyamine curing agent, mineral powder, and fibrous reinforcement are used to form the epoxy composite material. Conditions in which friction and wear stabilize through the formation of self-assembled structures are established in tribotechnical tests. The wear rate is studied as a function of sliding speed, load, and sliding distance. The effectiveness of gradual loading of the composite during tribological interaction is shown. This allows wearresistant surface structures to be created.
Keywords: wear rate; tribocontact surface; epoxy composite material; sliding speed; specific load

Cermet coatings based on Ni–Al alloys and titanium–chromium diboride are electrospark-deposited onto 40Kh steel. It is analyzed how the metal-to-refractory phase ratio in the electrode material and the deposition conditions influence the mechanical and tribotechnical characteristics of the coatings. The wear resistance and friction coefficients of the electrospark-deposited coatings are shown to depend on the friction speed and loading. The cermet coatings show high tribotechnical characteristics (I = 1–5 μm/km, f = 0.2–0.25) at speeds to 12 m/sec and loads to 4 MPa in dry friction conditions. These characteristics can be controlled by varying electrode chemical composition and deposition conditions.
Keywords: electrospark-deposited coating; wear resistance; hardness; cermet material; titanium–chromium diboride

Effect of Molybdenum Additions on the Microstructure and Properties of WC–W2C Alloys by I. Yu. Trosnikova; P. I. Loboda; O. I. Bilyi (219-224).
The paper examines how additions of 5, 10, and 20 wt.% molybdenum influence the structure, stress–strain state, phase composition, and size of phase components in WC–W2C alloys. It is found that 5 wt.% molybdenum leads to 30% increase in the microhardness and twofold to threefold increase in the wear resistance of cast tungsten carbide compared to the alloy without additions. Higher molybdenum content of the WC–W2C alloys changes the phase composition and increases compressive stresses in the W2C matrix phase and tensile stresses in WC, (Mo, W)2C, and Mo2C inclusions.
Keywords: tungsten carbide; molybdenum; stress; microstructure; microhardness; wear resistance

The magnetoelectric effect in multiferroic materials is widely studied for its fundamental interest and practical applications. The magnetoelectric effect observed for single-phase materials like Cr2O3, BiFeO3, and Pb(Fe0.5Nb0.5)O3 is usually small. A much larger effect can be obtained in composites consisting of magnetostrictive and piezoelectric phases. This paper investigates the magnetoelectric properties of nickel ferrite Ni0.3Zn0.62Cu0.08Fe2O4–relaxor Pb(Fe0.5Ta0.5)O3–PbTiO3 bulk composite. The magnetic properties of the composite show a dependence typical of such materials, i.e., it consists of a dominating signal from the ferrimagnetic phase (ferrite) and a weak signal from the paramagnetic (antiferromagnetic) phase (relaxor). The magnetoelectric effect at room temperature was investigated as a function of a static magnetic field (300–6500 Oe) and frequency (10 Hz–10 kHz) of a sinusoidally modulated magnetic field. The magnetoelectric effect increases slightly before reaching a maximum at HDC = 750 Oe and then decreases.
Keywords: multiferroic materials; magnetoelectric composite; dielectric properties; magnetic hysteresis; magnetoelectric effect

Phase Equilibria in the Melting/Solidification Range of B–Mo–Ti Alloys by O. A. Potazhevska; A. A. Bondar; L. A. Duma; V. M. Petyukh; V. B. Sobolev; T. Ya. Velikanova (230-242).
As-cast B–Mo–Ti alloys and samples annealed at subsolidus temperatures are experimentally studied by X-ray diffraction and scanning electron microscopy with electron microprobe analysis. Solidus temperatures and temperatures of other phase transformations are measured by differential thermal analysis and pyrometry with the Pirani–Alterthum method. No ternary compounds are found in the examined alloys. Based on the data obtained, the B–Mo–Ti liquidus and solidus surfaces have been constructed for the first time.
Keywords: Ti–Mo–B; phase diagram; boride; liquidus; solidus; eutectic

Thermodynamic Properties of Al–Sc Alloys by M. O. Shevchenko; V. G. Kudin; V. V. Berezutskii; M. I. Ivanov; V. S. Sudavtsova (243-249).
The mixing enthalpies of liquid Al–Sc binary alloys (0.62 < xSc < 1) are determined by isoperibolic calorimetry at 1840 K. The thermodynamic properties of liquid Al–Sc alloys are described in the entire composition range using the ideal associated solution model. The thermodynamic activities of components in the Al–Sc melts demonstrate large negative deviations from the ideal behavior; the mixing enthalpies are characterized by significant exothermic effects. The minimum mixing enthalpy equals –32.7 ± 2.2 kJ/mol at xSc = 0.49. The experimental and literature data are compared.
Keywords: calorimetry; thermodynamics; melts; aluminum; scandium; activities; phase diagram