Powder Metallurgy and Metal Ceramics (v.49, #5-6)

Formation of dendritic copper deposit in industrial electrolysis by M. L. Osipova; I. B. Murashova; A. M. Savel’ev (253-259).
The paper examines variation in the structural characteristics of copper deposit in the electrolysis process. In spite of the extensive post-electrolysis treatment, the properties of the products are greatly dependent on the structure of particles formed during electrolysis. A method is described to monitor the electrochemical crystallization of dendritic copper deposit in an industrial electrolytic cell. The governing equation is completed with a parameter for 95% mean current efficiency of the copper deposit to use the model of dendritic growth on a cylindrical electrode to describe the crystallization of brittle copper. With this method, the growth of the dendritic deposit is videorecorded and the time dependence of cathodic overpotential is plotted. The data are processed to show the variation in the structural parameter of the dendritic deposit and to determine reliably the periods for removal of the powder from the cathode to decrease the yield of cathodic scrap and increase the powder homogeneity.
Keywords: copper; dendritic deposit; electrolysis; video recording of dendritic deposit growth; cathodic overpotential; variation in structural parameter

The paper examines the formation of a continuous series of titanium and chromium solid solutions with iron admixtures ground in an AIR-015M planetary-ball mill. A non-equilibrium cubic β-titanium phase forms under intensive milling of titanium and chromium powders due to decrease in the grain size to the nanoscale at relatively low temperatures (T < 0.3Tm). A continuous series of titanium–chromium bcc solid solutions is obtained owing to intensive milling in an AIR-015M planetary-ball mill and favorable conditions for the formation of a non-equilibrium structure of titanium.
Keywords: mechanochemical synthesis; chromium; titanium; solid solution; bcc structure

The production of powder alloy AD33 containing additional 1% Fe is examined. The structurization and properties of the powders and alloys formed under high-pressure water atomization are analyzed. There is a complex dependence of the particle size and nature of oxide films on their surface on the melt temperature, which has to be no more than 900°C. The strength of the powder alloy compacted under different conditions increases by 60–70% as compared with the conventional alloy (without iron) and corresponds to the strength of high-alloy aluminum alloys.
Keywords: dispersion-hardened; aluminum alloys; water atomization; grain-size distribution; strength

The paper determines the effective elastic properties of a model material containing pore channels with cross-sections as Y-shaped cracks centered at the nodes of a regular hexagonal network and having arms aligned with the links of the network. A unit cell of relative size $ 1 imes sqrt {3} $ consisting of two halves of adjacent cracks is considered. Effective Young's modulus and Poisson's ratio of the unit cell are determined for all combinations of relative arm lengths in 0.05 increments. The limits of variation in the effective elastic properties depending on the relative total projection of cracks onto the transverse deformation direction are established.
Keywords: fibrous structure; pore channels; Y-shaped cracks; elastic properties

Mechanical properties of Al–Cu–Fe alloys sintered at high pressure by Yu. V. Mil’man; N. A. Efimov; S. V. Ul’shin; A. I. Bykov; O. D. Neikov; A. V. Samelyuk (280-288).
The structure and mechanical behavior of bulk Al–Cu–Fe materials sintered at high hydrostatic pressure are studied at room temperature. Quasicrystalline Al63Cu25Fe12 and Al62.7Cu25Fe12Sc0.3 powders and Al66Cu18Fe8Cr8, powder, which is the quasicrystal approximant, are sintered at high pressure. The powders are obtained by high-pressure water atomization. At an optimal hot compaction pressure of 4.5 GPa, the porosity of the compact materials is lower than 2%. Sintering is conducted at 700°C. The stress-strain curves of quasicrystals and their approximants that are brittle in standard test conditions are obtained using indentation method. It is shown that the crystalline approximants of quasicrystals are much closer in their mechanical behavior to quasicrystals than to crystalline solids.
Keywords: quasicrystals; approximants of quasicrystals; water-atomized powders; sintering; indentation

This paper reports the outcome of an investigation into the effect of Al2O3 content on the microstructure and wear properties of Al–Al2O3 metal matrix composites. The Al–Al2O3 composites are prepared by a mechanical alloying method using Al2O3 powders up to 20 vol.% as reinforcement. Alloying is performed in a vibration mill using a ball-to-powder ratio 10:1 and a milling time varying from 30 to 100 min at a rate of 710 Hz. The prepared compositions are cold pressed at 630 MPa with a single action and sintered at 560°C for 30 min under Ar gas atmosphere. The experimental results show that the reinforcing phase Al2O3 is homogeneously dispersed in the Al matrix and the interface between Al matrix and Al2O3 is well formed. Wear tests are carried out under dry sliding conditions using a pin-on-disk testing machine at three different loads of 10, 25, and 50 N and at a sliding speed of 2.08 m/sec. Total sliding distances are selected as 400, 800, 1200, and 1600 m. It is seen that the wear rate decreases with increasing Al2O3 content and sliding distance at a sliding speed of 2.08 m/sec.
Keywords: Al–Al2O3 composites; mechanical alloying; wear

Structure and phase composition of composite detonation coatings based on TiCrB2 and ZrB2 by I. A. Podchernyaeva; E. A. Astakhov; A. P. Umanskii; A. D. Panasyuk; V. P. Konoval; V. M. Panashenko (295-303).
The detonation method is used to deposit TiCrB2–FeCr and (AlN–ZrB2–ZrSi2)–NiCr composite coatings on steel 45. The structure, microstructure, and morphology of the starting powders and detonation coatings are studied. Based on the distribution of elements and microhardness at the coating–substrate interface, the formation of the coatings is analyzed. It is shown that a transition zone forms at the coating–substrate interface due to mutual mass transfer. This zone promotes strong adhesion and gradual decrease in microhardness toward the substrate. High-temperature corrosion-resistant chromites and mullites, which can serve as a solid lubricant, form in the system containing a solid-phase multicomponent phase (AlN, ZrB2, ZrSi2). The coatings are thus expected to have excellent tribotechnical properties.
Keywords: coating; detonation spraying; microstructure; composite powders; titanium–chromium diboride; zirconium diboride; aluminum nitride; microhardness

Microwave absorptivity of refractory powders depending on particle size by A. V. Shpil’ko; E. V. Kirilenko; M. V. Soltis; V. Ya. Petrovskii (304-316).
The microwave absorptivity of refractory metallic compounds at 2.45 and 9.53 GHz is studied. It is ascertained that electromagnetic absorption is influenced by the grain size of absorbing particles: when it increases by 10 times, the absorptivity of ZrC, ZrSi2, HƒC, TaN, HƒN, ZrN, and NbC particles becomes higher by a factor of 7 and that of SiC, NbSi2, WC, B4C, MoSi2, and VN particles only by a factor of 2 to 4. It is connected with the physical properties of each compound: magnetic permeability (sign and magnitude), thermal e.m.f. (sign and magnitude), and active ac resistance. It is shown that stoichiometric impurity (namely, the formation of nonmetal vacancies) increases the microwave absorptivity, while the formation of substitution phases does not change the nature of microwave interaction. It is established that the morphology of particles with the same sizes does not influence the microwave absorptivity. It is proved that the measurement of absorption in weak fields can be used for nondestructive examination of refractory metallic compounds.
Keywords: refractory compounds; microstructure; powders; microwave absorption; stoichiometry; nondestructive inspection

Low-temperature heat capacity of samarium zirconate (Sm2Zr2O7) by A. R. Kopan’; M. P. Gorbachuk; S. M. Lakiza; Ya. S. Tishchenko (317-323).
The heat capacity of Sm2Zr2O7 is investigated for the first time over a temperature range of 60–300 K by adiabatic calorimetry. The values of heat capacity, entropy, enthalpy, and reduced Gibbs energy are determined in standard conditions: C° p (298.15 K) = 236.21 ± 0.94 J ⋅ mol.−1 ⋅ K−1; S°(298.15 K) = 247.3 ± 2 J ⋅ mol.−1 ⋅ K−1; Φ′(298.15 K) = 114.9 ± 1.7 J ⋅ mol.−1⋅ K−1; H°(298.15 K) − H° (0 K) = 39,479 ± 197 J ⋅ mol.−1.
Keywords: thermodynamics; heat capacity; enthalpy; entropy; reduced Gibbs energy; samarium zirconate

Decomposition activation of hydroxyapatite in contact with β-tricalcium phosphate by V. V. Skorokhod; S. M. Solonin; V. A. Dubok; L. L. Kolomiets; T. V. Permyakova; A. V. Shinkaruk (324-329).
The paper examines the phase interaction in mechanical mixtures of thermostable hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) powders depending on the annealing temperature, initial composition, and particle size with x-ray interpretation of phase changes. It is established that HA transforms into β-TCP through a dehydration reaction during annealing of the mechanical mixtures of HA and β-TCP powders. The dehydration reaction proceeds through interphase activation in which the limiting stage of nucleation disappears. The phase boundaries in the two-phase HA–TCP mixture are more permeable for water vapors than single-phase boundaries owing to their disordered structure.
Keywords: dehydration; interphase activation of decomposition; limiting stage of nucleation

Kinetics of destructive hydrogenation of Ti2Cu and γ-TiCu intermetallides by T. I. Bratanich; V. V. Skorokhod; O. V. Kucheryavyi (330-338).
The kinetics of Ti2Cu and γ-TiCu destructive hydrogenation is examined. The research focuses on Ti2Cu and γ-TiCu samples in the form of plates, powders, and compacted powders and ingots. It is determined that the hydrogen pressure, temperature, and surface area of the intermetallides proportionally influence the rate of destructive hydrogenation of Ti2Cu and γ-TiCu in general and of each component in particular: hydrogen dissociation, hydrogen diffusion, and reaction rates. It is shown that pressure has a greater effect on the maximum hydrogenation rate than temperature. Higher titanium content of the intermetallides, other conditions being equal, increases the rate of the reaction and thus of the destructive hydrogenation. The compaction of Ti2Cu and TiCu powders and ingots intensifies the destructive hydrogenation process. This is due to the formation of catalytic juvenile intermetallic surfaces and to additional self-acceleration of surface reactions through autocatalysis. Of all the examined samples, the compacted ingots have the best kinetic characteristics because of the smallest specific fraction of oxidized surface. This conclusion is very important for application of the destructive hydrogenation process.
Keywords: titanium; copper; intermetallides; destructive hydrogenation; rate

High-temperature oxidation of sprayed NiAl–Re coatings subjected to magnetic treatment by V. E. Oliker; E. N. Eliseeva; T. Ya. Gridasova; I. I. Timofeeva (339-346).
The effect of structural changes that occur in heat-resistant detonation-sprayed NiAl–Re coatings treated in the magnetic field on their oxidation is examined. It is shown that the surface of coatings subjected to magnetic treatment is rich in nickel and layers of nickel oxides form more intensively and to a greater depth (as compared with those without magnetic treatment) until a continuous layer of alumina forms in the scale. The removal of the nickel-rich layer uncovers aluminum-rich surface where a continuous protective layer of Al2O3 scale can be formed in high-temperature oxidation.
Keywords: scale; intermetallic coating; treatment in magnetic field

Anodic behavior of Al–Bi and Al–Sb alloys in 3% NaCl solution by M. O. Krasovskii; V. O. Lavrenko; L. M. Kostenko (347-350).
The methods of polarization curves and scanning electron microscopy are used to study the pitting corrosion resistance of Al–Bi (up to 4 wt.% Bi) and Al–Sb (up to 20 wt.% Sb) binary alloys in a 3% NaCl solution. With concentration of the alloying element to 0.1 wt.%, current density decreases and corrosion slows down. With higher concentrations of antimony and bismuth, the early passivation current density increases and the active region reduces on potentiodynamic curves. This indicates that the corrosion resistance of aluminum alloys decreases with greater content of the other phase (Bi or Sb).
Keywords: bismuth; antimony; aluminum; pitting corrosion; corrosion resistance; aluminum alloys

Formation of oxides on tungsten conductors heated by electric current by S. G. Orlovskaya; F. F. Karimova; M. S. Shkoropado (351-354).
High-temperature oxidation of tungsten is studied experimentally with the hot-filament technique. Steady-state oxidation of tungsten conductors (d = 300 μm, L=0.1 m) heated electrically is examined using optical pyrometry and electrothermography. Temperature profiles along the conductor and its average steady-state temperatures are measured for different current intensities. It is found out that tungsten trioxide filiform crystals show up on surface at 800 K. They grow up and gradually transform into acicular and lamellar crystals. Their size, morphology, and surface density depend on oxidation temperature and duration and on gas-phase pressure and composition. After the tungsten conductor is oxidized in air at atmospheric pressure (T = 1400 K) for 30 minutes, the mean lamellar crystals are 60 μm in diameter, the coarsest crystals reaching 320 μm.
Keywords: tungsten oxide; filiform crystals; high-temperature oxidation; temperature profile

Electrochemical and corrosion properties of composite electrolytic and galvanic Ni-based coatings. II. Corrosion resistance of thermally treated coatings by V. K. Medyukh; V. A. Shvets; R. M. Medyukh; V. N. Talash; Yu. A. Guslienko; N. R. Medyukh; I. V. Uvarova (355-359).
The paper examines the potential for increasing the corrosion resistance of composite electrolytic and galvanophoretic coatings under thermal treatment. The corrosion behavior of the coatings in a 3% NaCl solution is analyzed under various conditions of thermal treatment. It is established that thermal treatment of composite electrolytic Ni–B and Ni–Ti coatings has no effect on the corrosion resistance of the electrolytic coating itself or that placed on a substrate. At the same time, the galvanophoretic Ni–B–Mo2C coating shows high corrosion resistance after thermal treatment at 1100°C owing to the obliteration of porosity during liquid-phase sintering.
Keywords: composite electrolytic coatings; galvanophoretic coatings; polarization curves; stationary potential; hardening thermal treatment; liquid-phase sintering

Transmission electron microscopy is used to study the microstructure of fluorite-like solid solutions formed in pulsed-laser evaporation vacuum condensates. The dependence of the shape and size of the crystallites on the condensate temperature and the type of stabilizing oxide is shown. The effect of the admixture cation is explained using the phase diagrams for the relevant binary oxide systems. The significance of the phase size effect for the stabilization of the fluorite-like solid solutions formed in fine vacuum condensates is ascertained.
Keywords: vacuum condensates; pulsed-laser evaporation; fluorite-like solid solutions; phase size effect

Production of copper powder from rolled scale and its mechanical properties by T. A. Epifantseva; D. M. Fedorov; V. G. Kayuk; M. B. Shtern; I. D. Martyukhin (366-369).
A laboratory installation for producing copper powder from rolled scale metal has been developed. Processing modes are determined for reducing annealing to produce copper powder with optimal mechanical properties which are close to those of PMS-1 electrolytic copper. The installation developed at the Gas Institute of the National Academy of Sciences of Ukraine and the process of producing copper powder from scale material can be recommended for commercial use.
Keywords: schematic installation; production flowchart; porosity of compacts; particle size; specific surface area; elastic modulus; bending strength