Powder Metallurgy and Metal Ceramics (v.52, #3-4)

The structure of dendritic copper deposit changes during electrolysis: the upper thin elongated branches are finally replaced by coarse globules. Therefore, it is important to determine the period of deposit growth without forming coarse globular particles. This period may be established by analyzing the dynamics of deposit growth and the variation in cathode overpotential, which is a contributor to cell voltage drop and may be used to monitor the structure of cathode deposit. Copper powders PMS11 and PML0 are used to calculate variation in the cell voltage and evaluate the change in deposit structure. The calculations have determined the period of growing homogenous deposits of the copper powders.
Keywords: copper powder; commercial electrolytic cell; cathode overpotential; cell voltage; deposit growth period

Contact stresses in the deformation zone and average pressure during asymmetric rolling of metal powders by K. A. Gogaev; G. Ya. Kalutskii; V. S. Voropaev; A. S. Kolpakov (126-131).
Consideration is given to the contact normal stresses in the deformation zone on the drive rolls of different diameters rotating at the same angular speed during asymmetric rolling of iron and electrolytic titanium powders, as well as aluminum granules. The ratio of roll diameters is 1.12 to 1.42. It is established that the normal contact stresses on both rolls are much lower than those during conventional (symmetric) rolling. It is shown that during asymmetric rolling, the contact stress on the larger roll is lower than the stress on the smaller roll, regardless of the material being rolled and the density of the rolled product.
Keywords: normal contact stress; asymmetry; rolling; powder

Manufacture of hardmetal cutting plates using barothermal self-propagating high-temperature synthesis by S. M. Vaitsekhovich; V. M. Mikhalevich; V. A. Kraevskii (132-136).
A process for producing hardmetal cutting plates (synthetic cutting tool material) has been developed and implemented. It is established that the most rational and economically sound option is to introduce several die toolings with relevant service features in the manufacture of products by self-propagating high-temperature synthesis. Advantages of the factor characterizing stress stiffness have been revealed. They involve one-to-one correspondence between the values of this factor and possible cases of plane stress. Coordinates for analytical representation and geometrical interpretation of the limit state criteria are proposed.
Keywords: self-propagating high-temperature synthesis; powder billet; die tooling; stress state criterion; limit state criterion

Thermochemical microwave treatment of refractory nanopowders by O. B. Zgalat-Lozinskii; V. G. Kolesnichenko; M. V. Zamula; L. V. Solyanik; V. V. Garbuz; L. A. Klochkov; N. V. Dubovitskaya; A. V. Ragulya (137-143).
Titanium nitride and silicon nitride nanopowders are subjected to microwave treatment to stimulate reduction and nitration reactions. It is established that oxygen content of the nanopowders after microwave treatment is 30–60% lower than that of the starting powders. It is also studied how the efficiency of thermochemical treatment and the particle-size distribution depend on the amount of the phase that absorbs microwave energy.
Keywords: microwave heat treatment; refractory compounds; nanocrystalline powders; titanium nitride; silicon nitride

Effect of starting powder properties on the structure and mechanical characteristics of Al–8Cr–1.5Fe alloy for high-temperature applications by O. D. Neikov; A. I. Sirko; N. P. Zakharova; N. A. Efimov; G. I. Vasil’eva; A. O. Sharovskii; A. V. Samelyuk; V. A. Goncharuk; R. K. Ivashchenko (144-153).
A high-temperature Al–8Cr–1.5Fe alloy has been developed for applications in the range from room temperature to 300°C. The billets are obtained in two ways: using gas-atomized and water-atomized powders. Structural analysis shows that particles of the second phase in the water-atomized powders are finer and their number in the aluminum matrix is greater than that in the gas-atomized powders. The rods extruded from the water-atomized powders have much higher hardness, ultimate strength, and yield stress than those from the gas-atomized powders, plasticity being acceptable at all temperatures (20, 190, and 300°C). An additional powder metallurgy operation—pulsed hot pressing—does not increase the strength of billets from either the water-atomized or gas-atomized powders. The alloy based on the water-atomized 0–63 μm powder shows the maximum strength: 483, 332, and 261 MPa at 20, 190, and 300°C, respectively.
Keywords: gas-atomized powders; water-atomized powders; high-temperature aluminum alloy; structure; strength; strain hardening

The paper presents results of electron microprobe, X-ray diffraction, and differential thermal analyses of master alloys produced by reaction synthesis of Al–Ti–C powder mixtures of various compositions. It is shown that heating of all stating mixtures leads to in situ precipitation of titanium carbide particles and complex titanium–aluminum carbides. Spherical titanium carbide particles are the predominant strengthening phase in samples with high carbon content (10–13%) and disordered elongated acicular grains of complex titanium–aluminum carbides in samples with minimum carbon content (6%) and relatively high aluminum content (40%). It is established that 45 wt.% Al–11 wt.% C–44 wt.% Ti master alloy with practically equal aluminum and titanium contents is characterized by the finest strengthening phase particles after thermal synthesis.
Keywords: reaction synthesis; master alloy; metal-matrix composite; precipitation strengthening; aluminum; titanium carbide

Phase composition and properties of hot-pressed AlN–BN materials by O. M. Grigor’ev; T. V. Dubovik; N. D. Bega; V. I. Subbotin; A. O. Rogozinska; O. D. Shcherbina; I. L. Berezhinskii; A. A. Rogozinskii (161-166).
The effect of hot-pressing temperature on the phase composition and properties of AlN–BN materials with addition of Y2O3 or SiC is studied. The composites have higher density and mechanical strength than the hot-pressed AlN–BN material without additions and retain its good insulating properties, thermal and chemical resistance, and adequate machinability.
Keywords: aluminum nitride; boron nitride; yttrium oxide; silicon carbide; hot pressing; density; mechanical strength

The crystallinity and aromaticity of carbon modifications are found to be the main criteria for the mechanochemical synthesis of titanium carbide. A mixture of carbon black and graphite is promising for the mechanochemical synthesis. The titanium carbide synthesized by this technique is shown to have high sorption capacity.
Keywords: titanium carbide; mechanochemical synthesis; renewable vegetable feedstock; mechanical alloying; aromaticity; structure of carbon modifications; natural graphite; activated carbon; adsorption; carbon composition

Some trends in the development of wear-resistant functional coatings by I. A. Podchernyaeva; D. V. Yurechko; V. M. Panashenko (176-188).
Based on analysis of literature data on coatings playing a role of solid lubricants, prospective research areas have been identified. Two categories of coating materials are considered: with hardness lower than 10 GPa (polymers, soft metals, halides, dichalcogenides of transition metals, sulphates of alkaline earth metals, graphite) and with hardness higher than 10 GPa (oxides, carbides, nitrides, borides of transition metals, carbon-based composites). Methods of their deposition and surface structuring are discussed as well. The greatest effect is observed when coatings are deposited using combined techniques involving surface structuring. The development of new nanostructured high-temperature composite coatings that can adapt to extreme performance conditions is regarded as the most promising area of research for the next decade.
Keywords: solid-lubricant wear-resistant coating; deposition method; combined coating; nanocomposite coating; microsurface structuring

Effect of grinding time on the structure and wear resistance of SiC–Al2O3 ceramics by A. P. Umanskii; A. G. Dovgal’; V. I. Subbotin; I. I. Timofeeva; T. V. Mosina; E. N. Polyarus (189-196).
The effect of time during which SiC–50% Al2O3 is ground in steel drums on the particle size and phase composition is studied. The optimum hot-pressing temperature leading to complete shrinkage is determined in relation to grinding time. The composition and structure of the hot-pressed ceramics and their influence on the wear resistance in friction against a steel counterface are analyzed. The wear resistance of the ceramics monotonically decreases from 23.4 to 3.8 μm/km when grinding time increases from 1 to 16 h and increases to 5.8 μm/km for a grinding time of 32 h. The friction surfaces of SiC–Al2O3 ceramics are examined, and their wear mechanisms are established.
Keywords: ceramics; silicon carbide; iron milling; wear resistance; wear mechanism

This study focuses on toroidal elements having dimensions 3.1 × 1.5 × 1.4 mm and composition, mol.%: 37.6 Fe2O3, 38.1 MnO, 9.3 MgO, 11.7 ZnO, 3.3 CaO. It is shown that increase of the innerto-outer diameter ratio of the toroids leads to higher squareness of the hysteresis loop. The geometry of the samples and gradients of coercive force H c caused by structural heterogeneity influence the shape and squareness of the hysteresis loop. In the absence of oxidation, the surface layers of elements have lower H C than the inner ones because their magnetic reversal begins in weaker fields, promoting smooth transition from the horizontal to descending section of the hysteresis loop. The nonequilibrium oxidation of elements cooled down to the hardening temperature leads to an increase in H c: to a greater extent on the surface and to a smaller extent inside the toroids. As a result, the upper half of the descending branch of the hysteresis loop becomes steeper, while the lower half more shallow. Isothermal holding at the hardening temperature reduces the gradients of H c and the squareness of hysteresis loop.
Keywords: ferrite; toroidal element; magnetic hysteresis loop; hysteresis loop squareness; coercive force; microstructure; sintering; hardening; annealing

Vertical sections of the Al2O3–HfO2–Er2O3 phase diagram by Ya. S. Tishchenko; S. M. Lakiza; L. M. Lopato (204-211).
For a more complete description of the Al2O3–HfO2–Er2O3 phase diagram, three vertical sections are constructed in a wide temperature and composition range. The Er2O3 corner bisector shows the Er2O3-rich region of the ternary phase diagram and reveals the mechanisms of Er2O3 phase transformations: XHAB. The isopleth at 10 mol.% HfO2 (10H) shows the Al2O3–HfO2–Er2O3 constitution near the Al2O3–Er2O3 binary bounding system. The HfO2 corner bisector discovers the HfO2-rich region of the ternary phase diagram and the mechanisms of HfO2 phase transformations: FTM.
Keywords: hafnia; alumina; erbia; phase diagram; vertical sections; eutectic materials

High-temperature X-ray diffraction is used to study the evolution of phase states of rapidly solidified Fe64.9Mo19.6Cr14.5C (at.%) alloy during heating from room to solidus temperatures. The α- and β-Mn-like phases (χ and π, respectively), as well as bcc phases of various composition (α1, α2, α), η-carbon intermetallic (M6C), and R- and fcc phases are identified in the alloy. It is established that the χ-phase is stable in this alloy at high temperatures: it forms during heating in the range 973–1073 K, changes its chemical composition in the range 1073–1273 K, which remains unchanged at 1073–1473 K, and decomposes in the range 1473–1523 K; when it is heated, its relative amount and lattice parameter symbatically change from 20 to 55 wt.% and from 0.9061 to 0.9170 nm, the coefficient of thermal expansion being 16.65∙10–6 K–1. The existence of equilibrium regions with participation of the stable χ-phase, γ + α + χ + R, χ + γ + η + α, χ + η + γ + α, and χ + α + η + R, has been established in the Fe–Mo–Cr–C phase diagram for the first time. It is shown that the π-phase, found in the initial spinning alloy, is metastable. This phase abruptly changes its composition near 842 K and completely decomposes in the range 923–1073 K. When heated in the range 293–923 K, its relative amount and lattice parameter vary from 50 to 8 wt.% and from 0.6346 to 0.6401 nm, respectively, the coefficient of thermal expansion being 2.083∙10–6 K–1. The coefficients of thermal expansion of the η- and α-phases are 15.257∙10–6 and 7.117∙10–6 K–1. It is revealed that the temperature of full decomposition of the metastable β-Mn-like phase and appearance of the stable α-Mn-like phase in conditions of high-temperature X-ray diffraction is close to 978 K of α-Mn→ β-Mn polymorphic transformation in pure manganese. The high-temperature X-ray diffraction experiment indicates that π→α transformations of metastable phases and γ→α transformations of stable phases are diffusionless in this alloy.
Keywords: Mn-like phases; spinning method; high-temperature X-ray diffraction; diffusionless transformations; coefficient of thermal expansion; Fe–Mo–Cr–C phase diagram

Corrosion resistance of TiN films in 3% NaCl solution by A. S. Dranenko; V. A. Lavrenko; V. N. Talash (223-227).
The paper examines the corrosion behavior of textured polycrystalline and amorphous TiN films in 3% NaCl solution. It is shown that TiN films are oxidized by pitting corrosion. The main cause of corrosion instability of the textured polycrystalline films is interaction with impurities (in particular, oxygen and carbon) that form “clouds” around the grain boundaries. In case of the amorphous–crystalline films, the clouds are observed around associated interfaces. The corrosion resistance of textured polycrystalline films decreases with higher thermal stresses resulting from different coefficients of thermal expansion of the film and substrate. The corrosion resistance of amorphous–crystalline TiN films is about 700 times higher than that of bulk TiN powder material and 2 to 10 times higher than that of textured polycrystalline films.
Keywords: thin film; electrochemical corrosion; nanostructure; nitride

The paper describes the structural features and properties of condensed composites based on copper and refractory metals (W, Mo, Cr). These condensed materials have a lamellar structure with a hierarchy of macro-, micro-, and submicron levels. In the condensed materials based on copper and chromium, supersaturated chromium solid solutions form and decompose. Examples of applying the Cu–Mo, Cu–W, Cu–Cr, and Cr–Al2O1 composites condensed from the vapor phase to produce electric contacts and electrodes are shown.
Keywords: electron-beam evaporation–condensation; equipment; technology; structure; properties; application

Measurement of the tap density of metal powders by V. V. Artamonov; A. O. Bykov; P. O. Bykov; V. P. Artamonov (237-239).
The paper deals with one of the technological properties of metal powders, such as tap density. The objective is to analyze the state standard in force for determining the density of metal powders after tapping, taking into account operational experience in the field of powder metallurgy. It is established that the methods identified in the standard for determining the density of metal powders have contradictions and discrepancies. A simple and reliable device is proposed and manufactured for mechanical tapping of powders.
Keywords: metal powder; bulk density; shaking; tapping