Powder Metallurgy and Metal Ceramics (v.52, #9-10)

Effect of the Polarization Conditions on the Structural Properties of Zinc Dendritic Deposits by T. N. Ostanina; V. M. Rudoi; A. B. Darintseva; A. O. Cheretaeva; S. L. Demakov; A. V. Patrushev (489-497).
The influence of the polarization conditions on growth dynamics and structure of electrolytic zinc dendritic deposits obtained at room temperature from electrolyte with 0.3 mol/l zinc oxide and 4 mol/l sodium hydroxide is studied. The electrodeposition was performed at constant and pulsed current and potential. Constant-current chronopotentiometry was used to determine the surface area of the dendritic deposits in situ. The zinc microstructure was studied with electron microscopy. The deposit surface produced in pulsed current conditions intensively grew during the first 5 minutes of electrolysis and then changed insignificantly. In conditions of potentiostatic electrolysis, the coefficient K, which is the ratio of the deposit surface area to the substrate area, increased linearly with time; in pulsed potential conditions, it increased as a power-law functions. The deposits obtained in potentiostatic conditions show the lowest density that slightly varies with thickness. The density of the deposits crystallized in pulsed current conditions sharply increased upon the completion of active dendrite extension.
Keywords: dendritic deposits; zinc; electrodeposition; microstructure; pulsed conditions

The rolling of porous knitted wire mesh reinforced powder composite tapes is discussed. Data are reported on the effect of the architecture and structural and deformation features of knitted metal wire meshes on the processing parameters of reinforced composite tapes. It is established that using knitted wire as reinforcement for powder composites can help rolling difficult-to-form powder compositions. Despite their porosity, the resultant tapes have sufficient load-carrying capcaity and service properties required for some applications (electrode tapes, reinforced graphite seals).
Keywords: knitted metal wire products; rolling; powders; reinforcement; composite material

Production and Properties of Nanostructured Metal-Oxide Lead Zirconate–Titanate Piezoceramics by V. V. Prisedskii; V. M. Pogibko; V. S. Polishchuk (505-513).
Compact ceramic samples of lead zirconate–titanate are sintered from nanocrystalline (d av = = 25 nm) Pb(Zr0.52Ti0.48)O3 powder synthesized by thermal decomposition of an oxalate precursor. Conditions of nanopowder compaction have been found and kinetics of sintering and growth of nanocrystallites and coarser grains formed during consolidation have been studied. The lead zirconate–titanate ceramic samples consolidated from nanopowders are sintered at lower (by 300–350°C) temperatures and have higher (by 25–45%) dielectric and piezoelectric properties as compared to samples fabricated by conventional solid-state technology. Two-level grain structure is formed during sintering: nanocrystallites divided by low-angle boundaries and descending from initial nanocrystalline particles and consolidated coarser micrograins divided by high-angle boundaries. Sintering of the lead zirconate–titanate ceramics from nanocrystalline powders permits controlling the nanoscale size of crystallites and thus the nanostructured features of consolidated material.
Keywords: sintering; consolidation; nanocrystalline powder; piezoceramics; lead zirconate–titanate; electrophysical properties

Modern Processes of Producing Two-Layer Filtering Materials by P. A. Vityaz; A. F. Ilyushchenko; V. M. Kaptsevich; R. A. Kusin; I. N. Chernyak (514-522).
The paper describes developments of the Powder Metallurgy Institute (National Academy of Sciences of Belarus) in the field of producing two-layer permeable structures with a filtering layer 0.3–0.4 mm in thickness. The presented processes include: copressing of coarse powder and fine powder applied onto one of the shape elements with the help of binder; activation of sintering of fine metal fibers by fine powder particles; use of removable agents in plasma-assisted ion sputtering of coatings onto a porous powder substrate; self-propagating high-temperature synthesis in two-layer porous structures formed by different metals; and granulation of metal particles by pore agents. Examples of products made of the developed materials are provided.
Keywords: two-layer filtering materials; copressing of fine and coarse powders; powder and fiber materials; pore agent granulation; plasma-assisted ion sputtering; self-propagating high-temperature synthesis

Structure and Mechanical Properties of Titanium-Based Composites and Secondary Films Synthesized during Friction by A. G. Kostornov; V. F. Gorban’; O. I. Fushchich; M. V. Karpets; T. M. Chevychelova; A. D. Kostenko (523-529).
The structural state and mechanical characteristics of titanium-based composites and secondary lubricating films synthesized on their surface during dry friction are studied. It is found that secondary lubricating films with microheterogeneous and nanocrystalline (grain size <100 nm) structure are synthesized on the materials whose friction coefficient varies between 0.3–0.36 and wear between 1.91–68.3 mg/km at a high slip velocity (15 m/sec) and low pressure (0.8 MPa). These films determine the antifriction properties and performance of the materials. The mechanical characteristics of secondary lubricating films are higher than those of the composites. The antifriction properties can be evaluated from the ratio of the mechanical characteristics of the secondary lubricating films and the starting material: the smaller the ratio, the higher the antifriction properties of the composite.
Keywords: composite material; composition; structure; slip velocity; pressure; friction coefficient; wear; synthesis; secondary lubricating films; nanocrystalline state; phase composition; mechanical properties

Interaction between Hydrogen and Ground SmCo5 Alloy by I. I. Bulyk; A. M. Trostyanchyn; P. Ya. Lyutyy; V. V. Burkhovetskyy (530-538).
The paper determines the phase composition of the ground KS37 alloy after conventional and solid hydrogenation and disproportionation (SmCo5 being the main phase and Sm2Co7 the impurity phase) at a hydrogen pressure of 0.1–0.4 MPa and at temperatures up to 950°C for 5 h. It is established that products resulting from grinding of the Sm2Co7 phase interact with hydrogen to 560°C to form Sm5Co19 and unidentified phases. The SmCo5 phase disproportionates in the temperature range 560–650°C and pressure range 0.1–0.4 MPa for 2 h. Recombination at 650–950°C leads to the SmCo5, Sm2Co7, and Sm2Co17 phases. The SmCo5 content of the recombined alloy is the highest at 950°C. It is shown that grinding in hydrogen prior to hydrogenation, disproportionation, desorption, and recombination accelerates the disproportionation reaction owing to the formation of defects during grinding. The high-temperature recombination of the SmCo5 phase in hydrogen is confirmed.
Keywords: mechanochemical grinding; phase transformation; magnetic material; samarium–cobalt alloy; X-ray diffraction; metallographic analysis

Powder Metallurgy Production of Ti–5.4 wt.% Si Alloy. II. Structure and Strength of the Sintered Material by D. N. Brodnikovskii; N. I. Lugovoi; N. P. Brodnikovskii; V. N. Slyunyaev; N. N. Kuz’menko; A. D. Vasil’ev; S. A. Firstov (539-544).
The powder metallurgy production of porous Ti–5.4 wt.% Si material promising for solid oxide fuel cells is studied. Its structure and mechanical properties are examined. It is shown that compacting pressure in the range under study has no essential effect on the structure of green powder samples before sintering. The volume shrinkage of samples starts increasing with sintering temperature from 1300°C up to the solidus point. Variation in sintering conditions of compacts from the atomized Ti–5.4 wt.% Si alloy powder allows the material density to be changed in a wide range.
Keywords: Ti–Si alloy; quenching; centrifugal atomization; porosity; bending strength

Open-Cell Metal–SiC Composite Foams made by Electrolytic Codeposition on Polyurethane Substrates by V. Mikutski; O. Smorygo; D. Shchurevich; A. Marukovich; A. Ilyushchenko; A. Gokhale; R. Nadella; V. Sadykov; V. Usoltsev (545-550).
In this research, open cell Ni–SiC and Cu–SiC composite foams are produced by electrolytic codeposition on the polyurethane foam substrates using conventional metal plating electrolytes with suspended SiC nanoparticles. The method ensures the production of MMC open-cell foams; content of SiC inclusions in the metal matrix of up to 10 wt.% can be controlled by the SiC powder concentration in the electrolytes. Effects of the foam pore size (surface area) and the electrolyte composition on the content of SiC inclusions and the density gradient across the foam are studied.
Keywords: open cell foam; electrolytic replication; MMC structure; co-deposition; silicon carbide

Combined Functional Biocoatings on the VT-6 Alloy by N. V. Boshitskaya; I. A. Podchernyaeva; V. A. Lavrenko; I. V. Uvarova; D. V. Yurechko (551-559).
Electrochemical oxidation of spark-deposited coatings from intermetallic TiAl3 and TiN–3AlN nitride ceramics in 3% NaCl solution leads to a nanosized surface layer composed of titanium oxides of various composition: from higher to lower oxides toward the substrate. The highest corrosion resistance is shown by the intermetallic coating, which is confirmed by anodic oxidation polarization curves and layerwise Auger spectroscopy of protective titanium and aluminum oxide films. A combined biocoating is produced as follows: electrospark deposition of TiAl3 layer onto VT-6 alloy—electrochemical oxidation in 3% NaCl solution—deposition of hydroxyapatite layer—laser fusion. Energy-dispersive X-ray spectroscopy has revealed a wide adhesion area at the interface between the spark-deposited coating and hydroxyapatite, which agrees with smooth variation in microhardness in this area. The coating shows strong adhesion to the substrate and biocompatibility with the bone tissue.
Keywords: VT-6 alloy; combined biocoating; intermetallic TiAl3 ; TiN–3AlN nitride ceramics; calcium hydroxyapatite

Thermal Stability of Superhard Nitride Coatings from High-Entropy Multicomponent Ti–V–Zr–Nb–Hf Alloy by S. A. Firstov; V. F. Gorban’; N. I. Danilenko; M. V. Karpets; A. A. Andreev; E. S. Makarenko (560-566).
Nitride coatings with high hardness (60.0–65.0 GPa) are produced from a high-entropy multicomponent single-phase alloy containing five nitride-forming elements by vacuum arc deposition with application of pulsed implantation. These high values of hardness are characteristic of metals in the equiatomic alloy only in nanostructured state. The mechanical properties of the coatings annealed in the temperature range up to 1200 °C are studied. It is established that the coatings are solid solutions of high-entropy nitride with fcc lattice. The vacuum coatings inherit the same type of crystal lattice as that of the target (bcc). The crystal lattice of high-entropy vacuum coatings is formed through the mechanism revealed in the cast alloys. The parameter of this lattice is close to that calculated by Vegard’s rule.
Keywords: high-entropy alloy; multicomponent; vacuum arc deposition; nitride coatings; X-ray diffraction

Preparation of Al2O3–Ni Cermet Composites by Aqueous Gelcasting by A. Miazga; K. Konopka; M. Gizowska; M. Szafran (567-571).
The main objective of producing ceramic-metal composites is to improve the fracture toughness of the brittle ceramic matrix. Classical methods of powder metallurgy (such as isostatic or uniaxial pressing) are not capable of fabricating complex-shape elements. For this reason, colloidal processes have been applied recently in manufacturing of ceramic matrix composites. In the present work, Al2O3–3 vol.% Ni composites were prepared by aqueous gelcasting process and sintering in reducing atmosphere. The commercially available monomers 2-hydroxyethyl acrylate and N,N′-methylenebisacrylamide as cross-linking agents were used. The activator was N,N,N′,N′,-tetramethylenediamine (TEMED) and ammonium persulfate was added as an initiator of the polymerization process. Composite slurries were obtained from alumina powders (grain size 0.21 μm) and 3% (in respect to the total solid volume) of two nickel powders of different grain size (~10 and ~0.4 μm). The paper describes the rheological properties of the obtained composite slurries. The properties of green and sintered elements have also been presented. It was found that the presence of nickel particles had a significant influence on the slurry polymerization process. The green and sintered relative density was in every case higher than 57 and 97%, respectively.
Keywords: ceramic-metal composites; colloidal processes; aqueous gelcasting process; alumina and nickel powders; rheological properties; composite slurries; polymerization process

High-Temperature and Anodic Oxidation of Thin NiSi and NiSi2 Films by A. S. Dranenko; V. A. Lavrenko; V. N. Talash; M. V. Koshelev (572-576).
The high-temperature and anodic oxidation of thin NiSi and NiSi2 films produced by thermal annealing of Ni film on single-crystalline silicon is studied. Both types of oxidation lead to the formation of thin protective SiO2 layers. The high-temperature oxidation of NiSi films begins at 930 K, which is 100 K lower than that of NiSi2 films. When temperature increases, the mass increment of NiSi films becomes greater than that of NiSi2 films. This difference is three times as great at 1273 K, which is due to the difference in structure and stoichiometry. It is shown that the electrochemical corrosion resistance of films increases from Ni to NiSi and to NiSi2.
Keywords: thin film; high-temperature oxidation; electrochemical oxidation; protective SiO2 layer; silicide

It is established that structured phase formation in the diamond–(Fe–Cu–Ni–Sn) composite proceeds in the sequence different from that determined by the known phase diagrams. Depending on the processes of hot recompaction, the diamond−matrix transition zone attains a hierarchical structure and fully decarburizes through the formation of 5–40 nm Fe3C layers, thus enhancing the mechanical properties of the composite.
Keywords: diamond; iron; copper; nickel; tin, interaction; layer; transition zone; phase; composite; decarburization; pressure; temperature; structure; properties; wear resistance

Powder Technology for the Production of 44NKhTYu Elinvars by K. A. Gogaev; V. I. Ul’shin; V. S. Voropaev (588-593).
The paper studies the density and porosity of 44NKhTYu elinvar alloy blanks produced by powder technology, jet molding, and electron-beam remelting. It is shown that jet molding and solid-phase sintering of powders over a narrow remelting temperature range are the most promising. They can be used to make blanks and products whose density and porosity are close to those of cast alloy, the metallic yield being increased.
Keywords: elinvar alloy; powder technology; jet molding; electron-beam remelting; solidification; solid-phase sintering; density; porosity

The paper describes a new process of producing structural steel parts by molding mixtures of iron and iron oxide powders with a binder, reducing the oxides in vacuum with nanosized products from pyrolysis of the binder, and sintering. It is shown that this process has advantages over conventional pressing and sintering as well as the MIM process: it allows parts of complex shape to be produced and the cost of products to be decreased.
Keywords: iron oxide; iron powder; aldehyde single-step resin; metal preforms of complex shape; relative dynamic viscosity; pyrolytic carbon; density of parts; dimensional accuracy

Use of Fine Powders of Refractory Carbides and Nitrides for Inoculation of Iron–Carbon Alloys by A. I. Trotsan; V. V. Kaverinskii; I. L. Brodetskii (600-605).
Optimum process parameters for inoculating iron–carbon melts with fine powders are determined. It is shown that inoculants for low-carbon steel can be arranged in the order of decreasing efficacy as follows: NbN → TiN → ZrN → NbC. Inoculation of steel 20 during uphill casting to produce twoton ingots by introduction of fine 1–3 μm TiN powder at a rate of 0.12 kg/t has improved all mechanical properties: ultimate strength and flowability increased by 1.3–1.5 times, elongation and contraction by 1.2–1.3 times, and impact strength by 30–40 %.
Keywords: refractory carbides and nitrides; powder inoculants; steel; cast iron; mechanical properties

Joining Silicon Carbide Plates by Titanium Disilicide-Based Compound by E. Jacques; Y. Le Petitcorps; L. Maillé; C. Lorrette; L. Chaffron (606-611).
The present work is part of the Fourth Generation Reactor Program, which describes the methodology and results for joining SiC substrates by metallic silicides with SiC powder reinforcements. The severest temperatures in service are in the range of 1000 °C but short-time incursions at 1600 or 2000 °C have to be anticipated. One of the key issues is the joining of SiC f /SiC m composites to seal the combustible cladding. We describe the results for joining SiC substrates in liquid state using TiSi2. Joint integrity and joint strength can be improved by adding small SiC particles to the silicides powders. The assemblies are obtained in an inductive furnace. Cross-sections of the assembly, wettability tests, thermo-mechanical properties, and four-point bending tests are presented.
Keywords: brazing silicon carbide; ceramic–metal interface; ceramic matrix composites; intermetallic and disilicide compounds