Powder Metallurgy and Metal Ceramics (v.54, #5-6)

Phase Formation During Nitriding of Vanadium Disilicide by L. A. Krushinskaya; G. N. Makarenko; A. V. Kotko; I. V. Uvarova (253-258).
The evolution of microstructural and phase transformations during nitriding of mechanically preactivated vanadium disilicide powder is investigated by X-ray diffraction, chemical analysis, and transmission electron microscopy. It is established that, in the initial stage of nitriding (1000–1100°C), the phase formation is accompanied by the dispersion of near-surface zones of VSi2 particles and the formation of V2N and α-modification silicon nitride. With increase in the nitriding temperature, the phase formation is accompanied by the delamination of particles and the formation of mainly VN and silicon nitride of α- and α-modifications. Nitriding of a mechanically activated vanadium disilicide powder at 1400°C enables synthesizing a fine silicon nitride–vanadium nitride composite powder in a single process. The synthesized powder is formed as loose aggregates consisting of 50 nm particles.
Keywords: phase formation ; composite powder ; silicon nitride ; vanadium disilicide ; nitriding ; nanoparticles ; aggregates

The selected aspects concerning the shaping of ceramic powders by techniques using in-situ polymerization are presented. Optimization of the ceramic slurry composition, prevention of oxygen inhibition and analysis of gases released to the atmosphere during organics burnout are discussed. The presented results are performed for alumina and zirconia formed by gelcasting and gel-tape casting methods. The biggest challenges in shaping by above techniques lie in achieving homogenous green bodies of high mechanical strength and/or elasticity using low-toxic organic substances. The results of rheological measurements, which allow determining the polymerization idle time, DTA/TG analysis coupled with mass spectrometry, and SEM microstructure of green and sintered zirconia samples are presented.
Keywords: polymerization; gel-casting; zirconia; SEM; rheology

The data of structural and phase analysis of the master alloys produced by thermal synthesis from three compositions of Al–Ti–C powder mixtures are presented. It is shown that depending on the content ratio of titanium and carbon, the heating of the mixture leads to in situ formation of dispersed particles of titanium carbide TiC or complex titanium-aluminum carbides. Aluminum matrix composites with titanium carbide phase as reinforcement are produced by hot forging using synthesized master alloys. It is established that an increase in the carbide content entails an increase in the strength and hardness of composites, while ductility decreases. Therefore, the hardness and strength properties of the composites produced from a charge prepared in a drum tumbler mixer are significantly lower than those of samples produced from a charge prepared in a planetary mill, whereas the ductility of the latter is slightly lower.
Keywords: aluminum matrix composites; master alloy; hot forging; blending; grinding; strength; ductility; structure; carbide

Effect of Deformation Conditions on the Properties of Powder Material AMg5 by K. A. Gogaev; V. S. Voropaev; Yu. N. Podrezov; D. G. Verbilo; O. S. Koryak (274-280).
The effect of deformation conditions on the structure and mechanical properties of powder materials based on aluminum-magnesium alloys produced by ultra-fast crystallization of a melt atomized by high-pressure water is studied. Extrusion of powder compacts into a strip that is then subjected to symmetric or asymmetric rolling is used as a deformation process. The effect of the rolling conditions on the mechanical properties of powder material AMg5 with Zr and Sc added is investigated. It is shown that the use of fractional rolling of strips made of AMg5 powder alloys significantly increases the ductility of the material and has a weaker effect on the strengthening; asymmetric rolling being more efficient than symmetric one.
Keywords: aluminum alloys; powders; strain techniques; extrusion; symmetric and asymmetric rolling

Stability of Nanocrystals in 2D and 3D Systems in Ostwald Ripening by R. D. Vengrenovych; B. V. Ivanskyy; I. I. Panko; M. O. Stasyk; I. V. Fesiv (281-291).
The Chakraverty–Wagner distribution and generalized Lifshitz–Slyozov–Wagner distribution are compared within the LSW theory modified for the surface (2D system) and for the volume (3D system) with experimental histograms for nanocrystals (quantum dots) obtained by different techniques: electron-beam (molecular beam) epitaxy, liquid-phase epitaxy, and colloidal chemistry. Matching of the experimental histograms with theoretically plotted curves indicates the nanocrystals can grow (dissolve) in Ostwald ripening by two mechanisms simultaneously—diffusion and chemical reaction—which are controlled, respectively, by diffusion coefficient Ds (Dv) and kinetic coefficient β. The results of studies on the mechanisms whereby nanocrystals grow by Ostwald ripening may be used in processes of their synthesis.
Keywords: nanocrystals; nanoparticles; nanoclusters; nanosystems; growth mechanism; size distribution

Production conditions, physical, mechanical and tribotechnical properties of iron–high-carbon ferrochrome FKh800 materials alloyed with additives of chromium steels Kh13M2, Kh17N2, and Ni3B are investigated. It is established that a sintering temperature of 1250°C and isothermal holding for 60 min are the optimal parameters for producing such materials. It is revealed that adding steels Kh13M2 and Kh17N2 to the charge changes the structure of materials from two-phase to multi-phase, increases their wear resistance in dry friction against ShKh15 steel counterface by a factor of 2–2.5, somewhat increases their hardness, and decreases their bending strength).
Keywords: powder materials ; composite ; wear resistance ; iron ; complex chromium-iron carbide ; sintering ; hardness

The effect of the silicon content on the microstructure and mechanical properties of the SiCp/(1–x)Al–xSi (x = 7, 13, and 20 wt.%) composites, produced by spray deposition, are investigated. The average size of the eutectic Si and primary Si in the composite containing 20% Si (3.44 and 7.85 μm) is higher than that in the composites containing 13% Si (2.51 and 5.85 μm) or 7% Si (1.95 and 0 μm). With increasing in Si content, composites demonstrate an increase in the volume fraction of the primary Si and eutectic Si phases, and a decrease in the average distance between Si and Siphase particle. During tensile tests, the as-sprayed composite with a higher Si content shows an increase in elastic modulus, yield strength, and ultimate tensile strength, but a decrease in elongation. Both SiC particle/matrix debonding and Si decohesion are observed in all three composites, while the primary Si particle cracking is dominant in the composites containing 13 and 20% Si. The fracture reveals an increase in brittleness and in the tendency for the primary Si particles to crack, as the Si content increases.
Keywords: composites; microstructure; spray deposition; fracture

Behavior of Mo x Cr y Ta z Si2 Solid Solutions During Cyclic Heating in Air by I. V. Kud’; V. V. Pasichnyi; S. A. Ostapenko; L. I. Eremenko; L. S. Likhoded; D. P. Zyatkevich; I. V. Uvarova (304-308).
New oxidation- and heat-resistant materials based on a molybdenum solid solution (MoxCryTazSi2) have been tested by high-temperature cyclic heating and cooling in air in the range 300–1600°C. Compact samples of the solid solutions show high heat resistance. The oxidation resistance of the solid solution samples is much higher than that of MoSi2 in experimental conditions. The oxidation resistance of the solid solution is found to depend on its composition: the oxidation resistance of Mo0.60Cr0.36Ta0.04Si2 is two times higher and of Mo0.90Cr0.18Ta0.02Si2 is one order of magnitude higher than that of MoSi2. The oxidation resistance increases with Cr content up to 18 mol.%, but higher chromium amounts cause the characteristics to degrade because the strength of the protective surface film decreases. The MoSi2 solid solutions may be recommended as heat- and oxidationresistant materials for cyclic operation in air at temperatures up to 1600°C.
Keywords: oxidation resistance ; heat resistance ; silicides ; solid solution ; protective film

Electrospark-Deposited Coatings from Titanium and Tungsten Carbide Alloys: Mass Transfer Kinetics, Structurization, and Properties by Yu. G. Tkachenko; D. Z. Yurchenko; V. F. Britun; M. A. Vasil’kovskaya; V. T. Varchenko (309-317).
New WC, TiC, and TiB2 electrode materials have been developed for hard wear-resistant electrospark-deposited coatings on a metal substrate. The phase formation and structurization during hot pressing of these materials are studied. The effect of electrode production process on the mass transfer and coating properties is analyzed. The alloys have fine structure with 1–2 μm grains of the major fraction and 26–30 GPa hardness. The structure and functional properties of the electrospark-deposited coatings are examined. Their hardness is 14–24 GPa and thickness 40–120 μm. The new electrode materials show significantly higher scale resistance than T15K6 alloy coatings, and their abrasion and wear resistance in dry friction conditions suggests that they may be efficiently used to strengthen rapidly wearing parts of machines and mechanisms.
Keywords: electrospark hardening; electrode materials; erosion properties; coating properties; wear resistance

Composite Laser-Clad Coating on Titanium Substrate Using Pure Hydroxyapatite Powder by I. Smolina; P. Szymczyk; E. Chlebus; I. Ivashchenko; T. Kurzynowski (318-323).
Biocomposite (or bioceramic) materials have become very popular, especially for replacing some human bone parts, such as hip joints, knee joints, and producing implants for dentistry and others. It is supposed that cladding coatings with hydroxyapatite (HA) on a metallic substrate could be a good solution for implants. Production of laser cladding coatings using pure HA powder and titanium substrate is investigated.
Keywords: composite ; biocomposite ; laser cladding ; hydroxyapatite ; implant

Mixing Enthalpies of Al–Co Melts by N. I. Usenko; M. A. Shevchenko; N. V. Kotova; V. V. Berezutskii; M. I. Ivanov; V. S. Sudavtsova (324-330).
The partial mixing enthalpy of aluminum and the integral mixing enthalpies of liquid alloys in the binary Al–Co system are studied by high-temperature calorimetry at 1870 ± 5 K in the composition range 0 < xCo < 0.25. The energies of forming alloys of aluminum with metals in the second half of the 3d series are compared.
Keywords: aluminum ; cobalt ; mixing enthalpies ; high-temperature calorimetry

The wetting of some nonmetals coated with nickel and deposited in vacuum at 700°C using molten aluminum is studied. The sessile drop method and capillary purification are used. The threshold thickness of wetting is 150 nm for most materials and 400 nm for basalt. The high degree of wetting is observed because the metal melt wets better metal coatings than coated nonmetallic materials. Moreover, exothermic reactions to form aluminum nitrides take place in the system.
Keywords: exothermic reaction; composite material; soldering; wetting; aluminum; nickel coating

Corrosion of AlN–TiN Ceramics in 3% Nacl Solution by V. A. Lavrenko; V. A. Shvets; V. N. Talash (340-343).
The corrosion behavior of nitride ceramics of different compositions, particularly AlN–TiN, 3AlN–TiN, AlN–3TiN, and Ti2AlN, has been studied in seawater (3% NaCl solution). The methods of potentiodynamic polarization curves as well as X-ray diffraction and Auger spectroscopy are employed. The AlN–TiN samples show the highest corrosion resistance. When anodic polarization of the samples increases to +1.20 V (in relation to their stationary potential –0.22 V), their surface becomes the most passive one, and the samples no more pass into the solution. In case of more positive potentials, very thin protective films form on the samples, representing a two-phase coating consisting of AlOOH and Na4TiO4. Other composite ceramics are not characterized by such exceptional stability: longer regions of active dissolution are observed on the anodic polarization curves for these ceramics. For the samples of comparatively corrosion-resistant 3AlN–TiN ceramics, two-phase corrosion products, AlOOH and Al(OH)3, are formed. The AlN–TiN ceramic composite is recommended as the most corrosion-resistant material for seawater applications.
Keywords: AlN–TiN; 3AlN–TiN; AlN–3TiN; and Ti2AlN composites; corrosion resistance; seawater; protective surface films; method of polarization curves; X-ray diffraction; Auger spectroscopy

Mechanical Properties and Formation of Phases in High-Entropy CrFeNiCuCoAl x Alloys by M. V. Karpets; O. M. Myslyvchenko; O. S. Makarenko; V. F. Gorban’; M. O. Krapivka (344-352).
The effect of aluminum on the phase composition, microstructure, and mechanical properties of CrFeNiCuCoAl x multicomponent high-entropy alloys is examined. According to X-ray diffraction data, the phase composition of the alloys significantly varies depending on aluminum content: with higher aluminum content, the two-phase structure (mixture of FCC1 + FCC2 solid solutions) changes to a single-phase one (BCC solid solution). Scanning electron microscopy is employed to examine the alloy microstructure and determine the chemical composition of dendritic and interdendritic regions. The primary and secondary dendrites include all elements of the alloy. The interdendritic region has high content of copper as it possesses high pairwise positive enthalpy of mixing with most elements of the alloy. The microhardness increases from 3.1 to 8.4 GPa with greater aluminum content of the CrFeNiCuCoAl x system.
Keywords: high-entropy alloys; solid solution; microhardness; X-ray diffraction

Phase Transformations in High-Temperature Shock Compression of Carbon Black in Various Recovery Capsules by A. V. Kurdyumov; V. F. Britun; A. I. Danilenko; V. V. Yarosh (353-357).
Cylindrical recovery capsules without a central rod are used for the first time to study the phase transformations in carbon black under shock compression. Substantial differences in the regularities of transformations under shock compression in such capsules and in annular capsules (with a central rod) are revealed (the latter we used earlier to study the phase transformations in carbon materials).
Keywords: carbon black; shock compression; cylindrical recovery capsules; diamond; amorphous carbon phase

Development of a Method for Producing Heaters for High-Temperature Vacuum Treatment of Materials by A. N. Bukolov; Yu. A. Gribanov; I. V. Gurin; V. A. Gurin; Ya. V. Kravtsov (358-363).
This paper describes a method for manufacturing a high-temperature heating unit. We used graphite powder GSP-50 as a filler and sugar as a binder. The filler and binder were taken in the ratio 6 : 1. In manufacturing the heater, a paper shell is used to make a tubular preform. The paper mold is filled with a mixture of graphite and sugar and then compacted using a shaking table to density ρ = = 1.185 g/cm3. The unburned compacted preform is placed into a pyrolysis unit to be calcined at 900°C for 6 h. Subsequently, the carbonized preform is saturated in the pyrolysis chamber at 970°C for 48 h to density ρ = 1.175 g/cm3. The carbon–carbon heater unit produced in this way reduces the time for manufacturing the heater by one order of magnitude, decreases the consumption of electricity, natural gas, and carbon materials, and significantly increases the life of the heater. This method is suitable not only for the manufacture of heating units but also for other products having a hollow cylindrical shape for nuclear, aviation, and space industries.
Keywords: carbon materials ; heater ; pyrolysis ; gas-phase compression ; pyrolytic carbon ; carbonization

Drying of Water-Atomized Iron Powders by O. D. Neikov; Yu. V. Kolesnichenko; V. G. Tokhtuev (364-373).
The novel drying process combines conduction and convection in cocurrent flow of the heat carrier and dried material for conductive heat and mass transfer and in countercurrent flow of the air–vapor mixture and dried material for convective heat and mass transfer. The study of heat transfer and drying kinetics allowed the optimization of the drying modes for water-atomized iron powders. The heat flux transferred by conduction through the inner wall of the drum to the dried iron powder is 3.45 · 106 W/m2 at the beginning of cocurrent flow and 0.4 · 106 W/m2 at the end. The heat consumption for drying at the optimum amount of the air supplied to the drum for convective heat transfer in countercurrent flow of 983 kg/h reduces to 415 kJ/kg compared to 511 kJ/kg at 300 kg/h. The relative specific moisture of the air–vapor mixture is 0.034–0.045 because of a large amount of dry air and high temperature, i.e., the mixture is very far from saturation and cannot condense on the dried powder.
Keywords: iron powder; drum drier; drying kinetics; heat transfer; conductive–convective drying; air–vapor mixture; cocurrent flow; countercurrent flow; heat carrier

Ceramic–metal composites are an important group of materials for many applications due to their unique properties. The combination of the hardness, strength at high temperatures, chemical inertness of ceramics with ductile, electrical or magnetic properties of metal are not achieved in single-phase materials. However, the brittleness of ceramics is the main disadvantage, which is limiting the under stress performance of ceramics and ceramic matrix composites. Theoretical and experimental research is still concentrated on improving the fracture toughness by tailoring the microstructure of composites. The study of metal particles embedded into ceramic particles, their distribution, size, and the interfaces and their influence on mechanical properties of the composites are presented. The important role of production techniques is emphasized. Based on experimental results, the Al2O3–Ni system is discussed.
Keywords: fracture toughness; composite; ceramic matrix; ceramics; slip casting; gel casting

Erratum to: Phase-Structural and Electrochemical Properties of La2MgNi9 Alloys by Yu. V. Verbovytskyy; R. V. Denys; V. V. Shtender; I. Yu. Zavaliy (380-380).