Powder Metallurgy and Metal Ceramics (v.52, #5-6)

Features of Drying Water-Atomized Aluminum Alloy Powders by O. D. Neikov; G. I. Vasil’eva; V. A. Zhoga; I. I. Odokienko; V. G. Tokhtuev (241-246).
The kinetics of dehydration and heat drying of water-atomized aluminum powders is examined. It is shown that conductive vacuum ovens for reactive substances are inefficient. There is no device for the disintegration of particle aggregates in dryers of this type, which results in the risk of oxidation and thermal self-ignition of powders. Conduction–convection dryers provide disintegration of particle aggregates and continuous mixing and uniform distribution of the powder over the heating surface. The results are used to optimize the drying conditions for aluminum alloy powders and determine the maximum permissible drying temperatures depending on the moisture content of the powder.
Keywords: moisture content; chemical activity; disintegration of particle aggregates; dehydration; drying temperature; drying kinetics; thermal ignition; conduction–convection dryer; explosion safety

Dispersion and Carburization of Titanium Powders by Electric Discharge by O. N. Sizonenko; G. A. Baglyuk; É. I. Taftai; A. D. Zaichenko; E. V. Lipyan; A. S. Torpakov; A. A. Zhdanov; N. S. Pristash (247-253).
The effect of high-voltage electrical discharge in a titanium powder suspension in a hydrocarbon liquid on the dispersion and formation of titanium carbide is studied. The dependence of the resulting fine titanium carbide on the current density in the discharge channel is experimentally determined. The average diameter of powder particles after treatment with specific energy W sp = 1.3 MJ/dm3 at various current densities in the discharge channel reduces from a starting size of ~1000 to <1 μm. The increase of current density in the channel from 0.08 to 0.56 kA/mm2 (at specific energy W sp = 1.3 MJ/dm3) leads to an increase in the yield of titanium carbide from 32 up to 57 %.
Keywords: high-voltage electrical discharge; hydrocarbon liquid; synthesis; titanium carbide; current density; specific energy; X-ray diffraction

Metal Grinding in the Presence of Mechanically Degradable Polymer by V. P. Reva; D. V. Onishchenko (254-260).
Grinding of metal swarf in the presence of a mechanically degradable high-molecular compound intensifies the size-reduction and plasticizing processes and is accompanied by reduction reactions and desulfurization of metal particles. Mechanically degradable organics are used as solid-phase high-molecular compounds to promote metal grinding. A high-energy vibrating mill is employed to grind steel swarf, a single-crystal diffractometer for X-ray diffraction, and an infrared laser pyrometer to measure the temperature of the reactor walls during grinding. Polymethyl methacrylate is experimentally chosen as a high-molecular compound to generate active low-molecular components. The grinding of high-speed steel swarf together with the high-molecular organic compound leads to metal disintegration, which is a more energy-favored process that that occurring in the presence of low-molecular surface-active agents. The experiment has also demonstrated that there is no need to use labor-intensive annealing of the powder to eliminate mechanical work hardening since the vibration treatment of swarf in the presence of a degradable polymer leads to metal plasticizing. The time factor is used to describe the removal of adsorbed sulfur and that contained in steel from the metal and to describe the reduction of oxide films by the cracking products during mechanochemical treatment.
Keywords: vibrating treatment; high-molecular compound; polymethyl methacrylate; mechanical destruction; high-speed steel swarf; plasticizing; reduction; desulfurization

316L stainless steel powders with an average particle size of 20 μm were sintered at different heating rates under multi-field action in a Gleeble-1500D thermal simulation instrument. It was shown that both heating rate and sintering temperature directly affected the densification of sintering products, and the electric field not only provided the Joule heat for densification of preform, but also accelerated the diffusion of atoms, which leads to intensified sintering. Multi-field action includes the stress field, temperature field and electric field, and these fields work reciprocally rather than independently. The relative density of the sintered compact can be of the order of 88.9% at relatively low temperature (500°C) within relatively short sintering time (6 min).
Keywords: heating rate; sintering temperature; multifield coupling; Joule heat; diffusion

Coordinate grids are used to understand how the strained state of porous preforms evolves during hot forging in a semi-closed die with a cone-shaped flash gutter. The nature of strain tensors and the irregularity of porosity distribution over the forged pieces at various forging stages are established.
Keywords: hot forging; porosity; strain; die; flash gutter

Structure of Graphite Nanosheets Formed by Plasma Discharge in Liquid Ethanol by R. A. Sergiienko; S. Kim; E. Shibata; Y. Hayasaka; T. Nakamura (278-290).
Graphite nanosheets (GNSs) were synthesized by low-current plasma discharge in ultrasonically cavitated liquid ethanol. Effective elimination of the byproducts was confirmed by different techniques. The results indicated that there were two types of ordering along the crystallographic caxis in the GNSs, which were ABAB- and turbostratic stacking of successive graphene layers. Most of the GNSs were estimated to be between 8.8 and 30 nm thick, and their lateral sizes ranged from several hundred nanometers up to 11 μm with an average size of 4–5 μm. A simple mechanism for GNS formation by exfoliation of graphene layers covering the Fe–Pt alloy nanoparticles is proposed. The measured conductivity of GNSs was comparable to that of the reference graphene nanopowder and reference single graphene sheets.
Keywords: graphite nanosheets; carbon nanomaterials; electron microscopy; raman spectroscopy; plasma discharge; ultrasonics

Structure and Properties of Iron–High-Carbon Ferrochrome Powder Composites by V. A. Maslyuk; A. A. Bondar; V. B. Kuras’; M. I. Pidoprygora; V. M. Varchenko (291-297).
The physical and process properties of ferrochrome powder produced by grinding of lump high-carbon ferrochrome FKh800 are examined. It is found that the ferrochrome is pulverized sufficiently well, and its physical and process properties allow its use to make wear-resistant powder materials. The effect of ferrochrome content on the structure and properties of materials sintered in vacuum from iron powder compacts and powdered FKh800 is studied. The materials containing 30 wt.% FKh800 are found to have high density, bending strength, hardness, and resistance to abrasive wear.
Keywords: powder material; wear resistance; iron; complex iron–chromium carbide; sintering; hardness

Effect of Chromium, Vanadium, Al2O3–Cr, and Al2O3–V Coatings on The Strength of Uranium Dioxide Granules by A. P. Patokin; V. L. Kapustin; B. M. Shirokov; A. V. Shiyan (298-305).
The strength properties of uranium dioxide particles coated with chromium, vanadium, Al2O3–Cr, and Al2O3–V are tested by diametrical compression between two parallels planes in the temperature range from 20 to 900°C. It is shown that the strength of particles depends on the coating thickness and material, strength of the fuel core (kernel), loading rate, and experimental temperature. The particle strength grows with an increase in coating thickness and experimental temperature, reaching its maximum at 700 to 900°C. The coating fracture pattern changes from intercrystalline brittle (20–150°C) to plastic fracture (650–900°C). Methods are proposed for both statistical processing of test results and probabilistic particle strength assessment. It is shown that the strength of coated particles is well described by the Weibull distribution function, which makes it possible to predict the fracture of particles at any load. The particle strength versus load has been probabilistically evaluated at different temperatures.
Keywords: coating; particle; uranium dioxide; chromium; vanadium; strength; temperature

Structure and Properties of Wear-Resistant Spark-Deposited Coatings Produced with a Titanium Carbide Alloy Anode by Yu. G. Tkachenko; D. Z. Yurchenko; V. F. Britun; L. P. Isaeva; V. T. Varchenko (306-313).
The paper examines the phase and structure formation during hot pressing of titanium carbide electrode materials as well as the structurization and properties of spark-deposited coatings on steel substrates. The influence of the operating current used for erosion processing on the phase composition and hardness of the coatings is established. It is shown that the electrode materials with a certain composition and structure enable the electrospark deposition of 100 μm-thick coatings with hardness to 14 GPa. The mass of the material deposited on a steel substrate is three times higher than that formed using standard titanium carbide alloy TN20. The wear resistance of the coatings in abrasive and dry sliding friction is high, hence they may be recommended for protection of steel parts for severe wear applications.
Keywords: electrospark strengthening; electrode material; erosion property; coating property; wear resistance

The results of high-temperature diffraction, metallography, X-ray diffraction, electron microprobe analysis, and differential thermal analysis are used to specify the constitution of the Al–Pt system in the near-equiatomic range. The solidus surface is constructed for the first time on the composition triangle, and the constitution of the isothermal section at 1350°C in the range 50–100 at.% Pt of the Al–Cr–Pt ternary system is specified. The solidus surface consists of six single-phase surfaces corresponding to the ternary τ 1 phase (unknown structure), solid solutions based on platinum, and four binary phases existing in the Al–Pt system; nine ruled surfaces bounding two-phase volumes; and four isothermal planes forming invariant four-phase equilibria with participation of a liquid phase. When temperature decreases from subsolidus to 1350°C, stability of the phase based on the <(Al, Cr)Pt2> compound (low-temperature modification) increases substantially. This phase takes part in equilibria with other intermediate phases and with the Pt-based solid solution.
Keywords: solidus surface; phase; compound; isothermal plane; isothermal section

Enthalpy of SmAlO3 in the range 472–2252 K by A. R. Kopan’; M. P. Gorbachuk; S. M. Lakiza; Ya. S. Tishchenko; S. M. Kirienko (329-335).
The enthalpy increment of SmAlO3 is measured for the first time using high-temperature drop calorimetry in the temperature range 472–2252 K. The enthalpy values are used to determine other thermodynamic functions, such as heat capacity, entropy, and reduced Gibbs energy. Phase transitions from orthorhombic to trigonal structure and from trigonal to cubic structure are observed at 1055 and 2103 K, respectively. The phase transition at 1055 K is studied by differential thermal analysis. The enthalpies and entropies of phase transitions are determined.
Keywords: thermodynamics; heat capacity; enthalpy; entropy; reduced Gibbs energy; phase transition; samarium aluminate

The influence of surface treatment of high-capacity hydrogen sorbents (Zr–Ni intermetallics) with atomic hydrogen under cathodic polarization on their oxidation in a 30% KOH solution is studied. It is shown that no passivation film forms on ZrNi5 near the stationary potential under cathodic polarization, which is not the case with Zr2Ni and ZrNi. It is established that surface treatment with atomic hydrogen under cathodic polarization increases the rate of anodic oxidation of Zr2Ni → ZrNi → ZrNi5.
Keywords: high-capacity Zr–Ni hydrogen sorbents; cathodic polarization in 30% KOH solution; anodic oxidation rate

Hydrogen-sorption properties of (Ti, Zr)Mn2–x intermetallic alloy by V. G. Ivanchenko; V. A. Dekhtyarenko; T. V. Pryadko (340-344).
The microstructure and phase composition of 15.4 at.% Ti–30.2 at.% Zr–54.4 at.% Mn as-cast alloy as well as the phase composition of hydrogenation and desorption products are studied with optical microscopy and X-ray diffraction. It is found that the alloy under study is able to rapidly absorb hydrogen (up to H/Me ≈ 1.5) at room temperature and 0.6 MPa pressure without preliminary activation. It is shown that released hydrogen restores oxide films formed on the material during hydrogenation ensuring surface self-purification.
Keywords: intermetallic; hydride; hydrogenation kinetics; hydrogen storage capacity

Effect of magnetic treatment on the distribution of internal stresses in detonation spray WC–Co hardmetal coatings by V. Yu. Oliker; O. M. Polyarus; O. G. Gavrilenko; S. M. Chernega (345-350).
The influence of magnetic treatment on the mechanical properties of WC–Co hardmetal detonation spray coatings is studied. The type and size of internal stresses in coatings are determined. It is established that treatment in the magnetic field considerably decreases stresses (by 50–60%) but has no effect on the stressed state of the coating–substrate system. It is shown that magnetic properties of the substrate material have no influence on the results of magnetic treatment in our case.
Keywords: detonation spray coating; hardmetal; magnetic treatment; internal stresses; magnetic property

Production and Properties of Thick Magnetoresistive Films from Fine Ni3B Powders by B. M. Rud’; E. Ya. Tel’nikov; A. K. Marchuk; A. G. Gonchar; A. A. Rogozinskaya (351-356).
Pastes and films are produced from Ni3B powders of different particle sizes using thick-film technology: screen printing of pastes on a dielectric substrate and subsequent heat treatment in air without any protection. The phase composition and structure of the films are examined by X-ray diffraction and electron microscopy; the size of nanostructured elements (ferromagnetic Ni and dielectric layer of B2O3) formed during heat treatment of the films is determined. The magnetoresistance of the films in a 0−2 T magnetic field is measured. The influence of the external magnetic field on the magnetoresistance of the films is determined by spin-dependent tunneling of charge carriers.
Keywords: thick film; screen printing; heat treatment; structure; nanoparticles; magnetoresistance

Resorbable Calcium Phosphates Based Ceramics by T. Safronova; V. Putlayev; M. Shekhirev (357-363).
Resorbable monophase ceramics and ceramic composites based on calcium pyrophosphate (CPP, Ca2P2O7), tricalcium phosphate (TCP, Ca3(PO4)2), and hydroxyapatite (HAp, Ca10(PO4)6(OH)2) were prepared via thermal treatment of a HAp (Ca/P = 1.67) and CPP (Ca/P=1) mixture. High-temperature solid-state reaction between HAp and CPP leading to TCP formation was studied within the range 700–800 °C. The metastable α-TCP phase was observed in this range as a product of the solid-state reaction. The reaction had been completed before sintering of the powders started. The microstructure of CPP/TCP composites was found to be duplex-like, consisting of large CPP grains with smaller TCP grains among CPP ones. In the case of the monophase ceramics with starting HAp/CPP ratio corresponding to TCP, grain size was less than 300 nm.
Keywords: resorbable monophase ceramics; ceramic composites; calcium pyrophosphate; tricalcium phosphate; hydroxyapatite; high-temperature solid-state reaction; microstructure