Powder Metallurgy and Metal Ceramics (v.47, #11-12)

High-temperature interaction of carbon ferromanganese and copper powders by G. A. Baglyuk; L. A. Sosnovskii; M. B. Golovkova; A. A. Mamonova; N. V. Minakov (630-634).
The thermal synthesis of a master alloy produced from a mixture of carbon ferromanganese and electrolytic copper powders and interaction of the mixture components in various heating conditions are examined. It is shown that the interaction mainly involves the extraction of manganese dissolved in γ-Fe with copper melt followed by the formation (in cooling) of viscous Cu−Mn phases.
Keywords: master alloy; ferromanganese; copper; powder; alloy formation

Scholar, teacher, and scientific romantic by L. N. Paritskaya; Yu. S. Kaganovskii (638-645).

The relationship between the kinetics of the initial high-temperature creep of KCl and NaCl single crystals and the internal stresses induced during deformation is examined. The influence of the external stresses and temperature on the internal stresses is established. The possible mechanisms of the accumulation and relaxation of internal stresses that govern deformation kinetics are experimentally established and analyzed.
Keywords: relaxation; internal reverse stresses; creep; deformation; dislocation; disclination; low-angle dislocation boundary

Lateral propagation of intermetallic phases in coarse- and nano-grained Cu/Sn diffusion couples by Yu. S. Kaganovskii; L. N. Paritskaya; V. V. Bogdanov (652-659).
The kinetics of lateral Cu6Sn5 and Cu3Sn phase propagation in nano-grained thin-film and coarsegrained massive diffusion couples Cu–Sn is studied in a temperature range 160–180°C by optical microscopy, AFM, SEM, and energy-dispersive X-ray spectroscopy (EDS). To prevent surface diffusion and thus separate GB-diffusion contribution into the kinetics of phase propagation in nanograined structures, the surfaces of thin-film couples are covered by a thin carbon layer. It is found that the rates of lateral Cu6Sn5 and Cu3Sn phase spreading in thin-film couples exceed several times the spreading rates of the same phases over the surface of coarse-grained samples. The kinetics of lateral phase spreading both in thin-film and in massive diffusion couples obeys parabolic law. The kinetics of the phase propagation in thin-film couples turns out to be independent of the film thickness (in the range 40–200 nm), whereas it is rather sensitive to the grain size and GB structure. A and B regimes of GB reactive diffusion are found in the spreading Cu3Sn phase. Theoretical analysis of the phase propagation kinetics accelerated by GB diffusion is done and the phase propagation rates are calculated.
Keywords: Cu-Sn nano-grained thin films; coarse-grained massive polycrystals; reactive surface and grain boundary diffusion; intermetallic phases; lateral phase propagation; surface and grain boundary diffusion coefficients

Effect of microwave heating on diffusion in KCl–KBr single crystals by O. I. Get’man; V. V. Panichkina; P. Ya. Radchenko; A. V. Samelyuk; V. V. Skorokhod; A. G. Eremeev; I. V. Plotnikov; V. P. Matsokin (660-668).
The interdiffusion in single-crystal KCl–KBr diffusion couples, which form continuous solid solutions, is examined under microwave heating (24 GHz). The results are compared with data obtained under conventional heating. Electron microprobe analysis is used to examine the composition of the diffusion zone and microscopic analysis is used to examine its microstructure. It is shown that ion interdiffusion occurs faster under microwave heating than under conventional heating. The ascending diffusion of Cl and Br ions is revealed under microwave heating. The microstructure of the diffusion zone between KCl and KBr single crystals is highly heterogeneous after microwave heating and markedly different from that after conventional heating.
Keywords: KCl and KBr single crystals; microwave heating; interdiffusion

Sintering of nanosized tungsten carbide produced by gas phase synthesis by I. Zalite; J. Grabis; P. Angerer (669-673).
The preparation of ultrafine tungsten carbide bulk solids is of common interest in respect of the increased mechanical properties of such materials. Nanosized tungsten carbide powders are synthesized by ultra-rapid condensation from radio frequency plasma. The samples are compacted by hot pressing (HP) and spark-plasma sintering (SPS) at temperatures between 1500 and 1800°C. The raw powders and compacted samples are investigated with X-ray diffraction (XRD) to study the phase composition and crystallite size. The materials are also further characterized with electron microscopy methods (TEM and SEM). The objective of this study is to investigate the sintering behavior of the material, grain-growth development, and phase development in the WC-W2C system due to its technological importance.
Keywords: tungsten carbide; nanopowder; hot pressing; spark-plasma sintering

Dependence of antifriction properties of self-lubricating copper-based composite on the elastoplastic characteristics of tribosynthesis region by A. G. Kostornov; O. I. Fushchich; V. F. Gorban’; T. M. Chevychelova; A. D. Kostenko (674-679).
Microindentation is used to examine the elastoplastic deformation of a self-lubricating copper-based antifriction composite. Its performance and wear resistance in high vacuum and in open air are studied. It is shown that the friction skin synthesized during sliding in vacuum differs from the original material not only in the phase and chemical composition, but also in the structural state and mechanical characteristics: it has high hardness and is very susceptible to stress relaxation. The self-organization of the skin in the friction region leads to the self-lubrication effect and thus to low friction coefficient, high wear resistance, and good performance of the tribosystem in vacuum as a whole. It is established that the susceptibility of the friction skin synthesized in open air to stress relaxation is insignificant because of lead oxidation and thus its lubricating properties decrease as well. The wear resistance of the material decreases and the wear rate and friction coefficient increase in friction in open air.
Keywords: self-lubricating antifriction composite material; composition; structure; synthesis; temperature; structure; self-organization; friction; friction coefficient; wear resistance; mechanical properties

The paper discusses generalized characteristics of porous materials such as permeability, structure matricity, and pore tortuosity. The permeability factor for different materials (powder, fiber, foamed) is independent of porosity but is determined by the pore structure. The matricity and tortuosity substantially decrease with increasing porosity.
Keywords: generalized characteristics of pore space; permeability factor; tortuosity coefficient; matricity; high-porosity materials

Bulk changes and structure formation in solid-phase sintering of Ti−TiAl3 powder mixtures by G. A. Pribytkov; I. A. Andreeva; V. V. Korzhova (687-692).
The paper examines bulk changes and evolution of the microstructure and phase composition in solid-phase sintering of titanium and TiAl3 powder mixtures. Metallography, x-ray diffraction, and electron microprobe analysis are used to ascertain the sequence of structural transformations during isothermal holding in sintering. Samples with high content of TiAl3 intermetallide powder substantially expand during sintering since TiAl3 particles dissociate leaving pores behind and TiAl particles grow pushing each other away.
Keywords: powder titanium; powder intermetallide; solid-phase sintering; bulk growth; structure formation

Molybdenum-based oxidation-resistant MoSi2–Al2O3 and WSi2–Al2O3 coatings by V. I. Zmii; A. P. Patokin; V. L. Khrebtov; B. M. Shirokov (693-697).
Various studies and comparative tests are conducted on oxidation-resistant unmodified and modified MoSi2–Al2O3 and WSi2–Al2O3 silicide coatings in air at 1800 and 1900°C. Metallographic, x-ray diffraction, electron microprobe, and chemical analyses show that the introduction of alumina into molybdenum and tungsten disilicides improves their hardness and produces fine-grained silicides with high corrosion resistance. The composition with fine alumina particles (Ø < 0.1 μm) with the total alumina concentration from 3 to 15 wt.% in the coating is most favorable for improving the oxidation resistance of disilicides. It is shown that the high oxidation resistance of MoSi2–Al2O3 and WSi2–Al2O3 coatings is due to the presence of alumina in disilicides, which contributes to the formation of an external high-temperature oxide layer. This layer consists of α-Al2O3 and a mullite sublayer in which Al2O3 crystals are introduced into SiO2.
Keywords: coating; silicide; alumina; oxidation resistance; molybdenum; tungsten

Complex orthorhombic phase in the Al–Cr–Fe system by D. V. Pavlyuchkov; B. Przepiorzynski; B. Grushko; T. Ya. Velikanova (698-701).
The paper examines alloys in the ternary Al–Cr–Fe system in the region of compositions associated earlier with the extensive region of terminal Fe solid solutions in the hexagonal Al4Cr (μ) binary phase in which iron reaches almost 12 at.%. Scanning electron microscopy, x-ray powder diffraction, and electron diffraction show that the solubility of Fe in the μ-phase is substantially lower. Alloys Al76Cr19Fe5, Al76Cr16Fe8, and Al75Cr16Fe9 annealed at 1000 °C have a complex basecentered orthorhombic structure with a ≈ 3.27 nm, b ≈ 1.24 nm, and c ≈ 2.34 nm.
Keywords: metallides; phase equilibria; electron diffraction; scanning electron microscopy

Formation thermodynamics of erbium germanides by V. R. Sidorko; L. V. Goncharuk (702-706).
The Gibbs free energy, enthalpy, and entropy of formation of Er2Ge5, ErGe2, ErGe2-b(ErGe1,5), Er3Ge4, ErGe, Er11Ge10, Er5Ge4, and Er5Ge3 from solid components are determined by measuring the electromotive forces of high-temperature galvanic cells. The maximum thermodynamic stability is shown by Er5Ge3, which is the only congruently melting compound in the Er–Ge system.
Keywords: thermodynamics; Gibbs free energy; enthalpy; entropy; erbium; germanium

The heat capacity and enthalpy of Ce5Si3 are examined for the first time over a wide temperature range. The values of heat capacity, entropy, reduced Gibbs energy (J ⋅ mole−1 ⋅ K−1), and enthalpy (J ⋅ mole−1) at 298.15 K are determined: C P °(T) = 230.62 ± 0.93; S°(T) = 352.0 ± 2.8; Φ′(T) = 185.2 ± 2.8; H°(T)–H°(0 K) = 49,744 ± 249. The temperature dependences of Ce5Si3 enthalpy (J ⋅ mole−1) are determined as H°(T)–H°(298.15 K) = 19.934 ⋅ 10−3 ⋅ T 2 + 245.26 ⋅ T + 2,358,300 × T −1 − 82,807; H°(T)–H°(298.15 K) = 413.78 ⋅ T − 123,368 for 298.15–1564 K and 1745–1806 K, respectively. The enthalpy and entropy melting of Ce5Si3 are calculated as follows: T m  = 1564 ± 30 K, ΔH m  = 172.7 ± 12.2 kJ ⋅ mole−1, and ΔS m  = 110.4 ± 7.8 J ⋅ mole−1 ⋅ K−1.
Keywords: thermodynamics; heat capacity; enthalpy; entropy; Gibbs energy; silicide

X-ray analysis (in Cu and Mo radiation) is used to examine the phase composition of pseudoalloys for the first time. The pseudoalloys are formed in the liquid-phase sintering of W, Co, and Sn powders in hydrogen at 1200°C. After cooling, all pseudoalloys contain tungsten (intensive reflections) and W6Co7 (weak reflections) phases, γ′-phases of Co3Sn2, and CoSn2.
Keywords: tungsten; cobalt; tin; liquid-phase sintering; pseudoalloys; phase composition; compounds

Effect of the porous structure of thermal-barrier coatings on their heat conductivity by V. E. Oliker; T. Ya. Gridasova; A. A. Pritulyak (717-722).
A phenomenological model is proposed to show the dependence of the heat conductivity of a porous coating on the pore size using experimental data on ZrO2 + 7% Y2O3 coatings. To obtain plasmasprayed coatings with different structures, powders with different properties are used. The concept of critical pore size at a given porosity is proposed. It is the maximum pore size at which the heat conductivity depends not only on the total porosity but also on the pore size, which is especially important for materials with submicron and nanosized structural components. Since the free path of phonons scattered by pores depends on the distance between them, the concept of critical distance between pores is introduced. It is the maximum distance beyond which the heat conductivity depends on the integral porosity alone.
Keywords: thermal-barrier coatings; heat conductivity; pores; structure

Plasma parameters in electrospark deposition of silver coatings by V. D. Kurochkin; L. P. Kravchenko; L. O. Kryachko; O. M. Romanenko; V. V. Pukh (723-732).
Spectroscopic measurements and mathematical simulations are conducted to study the composition and parameters of spark discharge in depositing coatings with silver electrodes using an Élitron-22 generator. The effective temperature and electron concentration are measured at the maximum pulse current. It is shown that the intensity of spectral lines of atoms and ions is proportional to the erosion rates of Ag anode and Ag–C composite anode. Pressure in the plasma channel is calculated taking into account the pinch effect (~1 MPa). It is shown that the temperature of the material in the anode spot reaches the boiling point of Ag under about 1 MPa (~3200–3300 K). A mathematical model is used to study the influence of erosion rate, power, and pressure on the plasma parameters and the intensity of spectral lines of anode materials. The method proposed allows evaluating the efficiency of material transfer in the vapor phase during spark deposition of coatings. A method for quantitative spectral determination of carbon in Ag–C material using the spectral lines of doublecharged ions of Ag and C is developed.
Keywords: electrospark coatings; silver; plasma; parameters; mathematical simulation; spectroscopic measurements

Reduction of iron-containing metallurgical waste to obtain hydrogen with iron vapor method by V. S. Zenkov; V. V. Pasichnyi; V. P. Red’ko (733-742).
The paper examines the physicochemical processes that occur in the treatment of iron-containing metallurgical waste with the purpose of producing hydrogen with iron vapor method and subsequent processing the iron agglomerates. Iron oxides and reduced metal show high activity in the initial oxidation and reduction cycles. It is shown that the optimal oxidation–reduction temperature should be no more than 1000°C to prevent the intensive sintering of iron particles and decrease the activity in the reactive volume. The reduction process is most intensive in gaseous reducing medium.
Keywords: oxides; iron; hydrogen; waste; reduction; mechanism