Powder Metallurgy and Metal Ceramics (v.55, #7-8)

Physicochemical Characteristics of Nitrogen Sorption on High-Porous Powders of Graphene-Like Boron Nitride by V. V. Garbuz; T. F. Lobunets; V. A. Petrova; T. V. Tomila; L. S. Suvorova (379-385).
The porous structure of graphene-like boron nitride t-BNg powders is qualified. The material is homogenous and micro-mesoporous, with pores being distributed in the range 3.53–4.12 nm corresponding to 55% volume and 60% specific surface area of mesopores. The specific surface area of micropores calculated with the Dubinin–Kadlets method (t-method) is 28.3 m2/g and the specific surface area of mesopores calculated with the Barrett–Joyner–Halenda method is 141 m2/g. Powders of graphene-like t-BNg synthesized from carbamide contain impurities of polycondensed flat particles of boron oxonitride. Impurities as a refined sublimate (white powder) are separated out of the washed and dried t-BNg powder by subsequent vacuum heat treatment at 540 K and pressure to ≤1.0 Pa. The sublimate is identified as a heterocyclic six-membered dimer with molecular formula H(OH)[(BON)2](OH)H.
Keywords: graphene-like boron nitride t-BNg ; surface structure; impurity; boron oxonitride; treatment

The Taguchi robust design method is implemented for the optimization of experimental conditions in the synthesis of high-purity ultrafine copper powder (HUCP) in mass-production by the chemical reduction method. A reducing agent, reaction temperature, reducing agent weight, and a stirring rate are chosen as the major optimization factors and the conversion rate, particle size, and reaction time are chosen as the desired targets. It is established that the reducing agent and the reaction temperature are the most significant factors that affect the desired targets. Among the selected or designed factors, the optimal conditions for producing the HUCP are: NaH2PO2 · H2O as the reducing agent (level 2), temperature 70°C (level 3), a reducing agent weight of 8.14 kg (level 3), and a stirring rate 300 rpm (level 2). The study results for the three desired targets are in agreement with the prediction made by the Taguchi method. Furthermore, the pure (impurity <0.06%) facecentered cubic structure of the HUCP with 1.51 μm average particle size is extensively characterized and determined by inductively coupled plasma–optical emission spectrometer (ICP–OES), laser particle-size analyzer (DLS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis. This surfactant-free facility method is suitable for the synthesis of highpurity ultrafine copper powder by mass-production method.
Keywords: ultrafine copper powder; chemical reduction; Taguchi design; optimization

Effect of Physicochemical Characteristics of Diamond Micropowders on the Effectiveness of Their Separation in Magnetic Field by N. A. Oleinik; G. D. Il’nitskaya; O. N. Sizonenko; G. A. Petasyuk; G. A. Bazalii; V. S. Shamraeva; N. N. Tsyba; A. S. Torpakov; E. V. Lipyan (397-405).
The paper examines the effect of chemical and pulsed high-voltage electric discharge treatment of synthetic diamond micropowders on their mechanical and physicochemical properties, magnetic fraction composition, and separation characteristic, as well as effectiveness of their distribution in the magnetic field. It is shown that treatment with molten sodium hydroxide slightly decreases the specific surface area of the powder, and pulsed high-voltage electric discharge treatment increases its specific surface area and activates its energy state, improving the effectiveness of powder distribution in the magnetic field.
Keywords: synthetic diamond micropowder; pulsed high-voltage electric treatment; powder distribution; magnetic field

The effect of temperature–rate strain conditions in the free settlement of Cu–2% Ti billets sintered in the 100–700°C temperature range with a strain rate of 0.01 and 0.001 sec–1 on the power process variables and structurization are studied. It is observed some increase in the stress at ~400°C, while the general trend is the decrease in stress with increasing strain temperature. This is due to the dynamic strain age-hardening, accompanied with the release of the intermediate metastable and coherent β′-phase Cu4Ti. It is demonstrated that the intensity of compaction during free settlement increases with increasing temperature, strain rate, and the starting porosity of the samples. It is observed that with increasing degree of strain of the billet, it occurs a monotonic decrease in the average grain size of copper and crushing of titanium particles, whose intensity increases with increasing rate and temperature of the strain.
Keywords: sintered material ; degree of strain ; strain rate ; dynamic softening ; stress ; compaction ; structure

In the present study, aluminum metal matrix composites reinforced with alumina particles are fabricated through the warm accumulative roll bonding (ARB) process. The microstructure of the composites shows the excellent alumina particle distribution in the aluminum matrices after four cycles of ARB. The microstructure and mechanical properties of composites have been studied versus different contents of alumina particles by tensile test, Vickers microhardness test, and scanning electron microscopy. The results indicated that strength and average microhardness of the ARB-processed material improved by increasing volume percent of alumina particles.
Keywords: metal-matrix composites; mechanical properties; electron microscopy

The optimization of compacting processes for two-component model systems consisting of brittle and plastic components is discussed. Fe–FeSi and Al–FeSi compositions with different volume content of the plastic component are tested. The compaction is conducted by pressing with different compacting force. Mechanical properties of cylindrical compacts are determined by axial compression test and the Brazilian test. It is established that the content of brittle component must be ≤ 60% and the compaction force must be ≥ 400 MPa. With increasing compaction force, the strength of the compacts increases significantly. It is established that the application of both iron and aluminum as binder is acceptable. However, iron and aluminum compositions are the best for low and high content of the brittle component, respectively.
Keywords: powders ; cast iron ; inoculant mixtures ; rolling ; strip

A novel powder metallurgy method, based on preparation of powder mixtures of copper with 0.5, 1, 1.5, 2, 2.5, 3, and 5 wt.% of nanographite particles ~50 nm in size, is used to produce Cu-nanographite electrical contact materials with flake microstructure. The dispersion of graphite nanoparticles in the Cu matrix is examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Morphology, particle size, and apparent density of flake powders are investigated. Microstructure, density, electrical conductivity, and hardness are studied for green and sintered samples. The composites reinforced with lower graphite nanoparticles content (0.5 wt.%) exhibit much lower agglomeration content, while the composites reinforced with higher graphite nanoparticles content (5 wt.%) showed higher agglomeration content. It is found out that the electrical conductivity of the sintered Cu-nanographite electrical contact materials decreased from 76.92 to 68.28 IACS by graphite nanoparticle addition. The maximal (~34) and minimal (~20) Brinell hardness is obtained for the monolithic Cu sample and 5 wt.% graphite nanoparticle reinforced Cu electrical contact materials, respectively.
Keywords: electrical contacts; PM materials with flake microstructure; nanographite; mechanical milling

Conductive Film Materials Based on Thermally Stable Fluorine-Containing Polyamide and Nickel Boride by A. V. Paustovskii; B. M. Rud’; V. E. Shelud’ko; E. Ya. Tel’nikov; N. I. Siman; P. S. Smertenko; V. V. Kremenitskii; Yu. I. Bogomolov (437-444).
The development of resistor materials science and, namely, the feasibility of developing a composite film material based on the thermally stable polyamide and nickel boride as current-conducting filler, is considered. A process for producing films is developed: the films are obtained by coating the glass substrate with polymer solution with a pre-dispersed filler, followed by forming at 80°C with subsequent drying at 150°C until constant weight. The microstructure and topography of the film surface is studied by SEM and AFM. The formation of two-layer composite with the formation of conducting cluster (when the content of the conducting phase is >30 wt.%) from the substrate side is shown. Volt-amps diagrams are studied and analyzed by the differential method. The R(T) dependence is obtained and the temperature resistance coefficient is determined; the latter is positive and its value is 1.67 · 10–3 °C–1.
Keywords: polyamide matrix; filler; nickel boride; conductivity; volt–ampere characteristics; temperature resistance coefficient

Effect of the Starting Powder Mixture on the Porosity and Corrosion Properties of Sintered Titanium in Corrosive Media by I. M. Pogrelyuk; O. V. Ovchynnykov; A. A. Skrebtsov; Kh. S. Shvachko (445-453).
The protective properties of powder metallurgy titanium are investigated. The effect of the composition of the starting powder material on the structure of compacted samples and corrosion resistance in a 20% aqueous solution of the hydrochloric acid is revealed. It is established that the corrosion rate of the sintered titanium is two orders of magnitude higher than that of titanium produced by conventional technique. Adding the titanium hydride powder to the starting powder material ensures the formation of compacted structure with lower porosity and higher corrosion resistance (by a factor of 1.7–5.6).
Keywords: sintered powdered titanium; titanium hydride powder; corrosion resistance; corrosion current density; chloride acid

Brazing Oxide Ceramics via the Ductile Interlayers of Niobium and Noble Metals by Yu. V. Naidich; I. I. Gab; T. V. Stetsyuk (454-457).
Optimized processes for obtaining the braze-welded joints of oxide ceramics based on Al2O3 and ZrO2 by pressure welding of ceramics with ceramics and ceramics with metals are developed. It is established that these braze-welded joints are prepared in the 1300–1600°C temperature range with pressure holding for 30–120 min under 15–25 MPa. The samples of welded pilot products that can be operated in both neutral and protective environment (up to 1500–1800°C) are produced according to the processes developed.
Keywords: niobium; platinum; palladium; oxide ceramics; braze-welded joint; pressure welding

Secondary Ion Emission of High-Entropy Cr14.3Mn14.3Fe14.3Ni28.6Co14.3Cu14.3 Alloy by S. A. Firstov; N. A. Krapivka; M. A. Vasiliev; S. I. Sidorenko; S. M. Voloshko (458-463).
To understand the unique mechanical properties of high-entropy alloys, it is important to know the nature and strength of interatomic interactions between similar and dissimilar atoms. In this regard, the objective of this study is to use the phenomenon of secondary ion emission for Cr14.3Mn14.3Fe14.3Ni28.6Co14.3Cu14.3 alloy with fcc structure. The yield of secondary ions for all alloy components and corresponding pure metals is quantitatively compared for the first time and an equation is proposed to calculate the atomic bond energy based on the existing models of secondary ion emission mechanism. Compared to pure metals, the bond energy increases in the alloy for Cr and Fe atoms. The greatest decrease in the bond energy is observed for Mn atoms. Reduction in the bond energy for Co and Ni is insignificant. It is suggested that the atomic interaction energy is influenced by changes in the local electron density in fusion as compared with pure metals.
Keywords: high-entropy alloy; secondary ion emission; atomic structure; interatomic interaction; bond energy

Heat Capacity of Yb4Hf3O12 at 57–302 K by A. R. Kopan’; M. P. Gorbachuk; S. M. Lakiza; Ya. S. Tishchenko (464-468).
The heat capacity of Yb4Hf3O12 is studied for the first time in the range 57–302 K by adiabatic calorimetry. It is shown that Cp of ytterbium hafnate changes monotonically and no anomalies are observed. Temperature dependences of the principal thermodynamic functions in the range 10–300 K are obtained. The heat capacity, entropy, reduced Gibbs energy, and enthalpy are determined for standard conditions: C p ° (298.15 K) =408.4 ± 1.6 J · mol–1 · K–1, S°(298.15 K) = 410.5 ± 3.3 J · mol–1 · K–1, Φ′(298.15 K) = 187.2 ± 2.8 J · mol–1 · K–1, and H°(298.15 K) − H°(0 K) = = 66566 ± 333 J · mol–1. The difference between the experimental heat capacities and those evaluated by the Neumann–Kopp rule of additivity (as a weighed sum of heat capacities of oxides) in the range 70–300 K is no more than 4.65%, while the difference in C p ° (298.15 K) is 0.7%.
Keywords: thermodynamics; heat capacity; enthalpy; entropy; reduced Gibbs energy; ytterbium hafnate Yb4Hf3O12

Anodic Polarization of Titanium Carbide TiC x in 3% NaCl Solution in the Homogeneity Range by V. A. Shvets; V. A. Lavrenko; V. N. Talash; A. D. Panasyuk; Yu. B. Rudenko (469-476).
The potentiodynamic polarization curves, X-ray diffraction, energy-dispersive X-ray spectrometry, and Auger electron spectroscopy are employed to study the kinetics and mechanism of electrochemical oxidation of stoichiometric and nonstoichiometric samples of titanium carbide TiC x in the homogeneity range (x = 0.5–1.0). The content of TiO and TiO2 tends to decrease in the surface film on all compounds in the TiC0.6 → TiC1.0 row, with a very small amount of the TiO2 phase in the scale. The stoichiometric TiC1.0 sample shows the highest resistance to anodic oxidation because it has the strongest Ti—C bonds formed completely in its lattice.
Keywords: titanium carbide in homogeneity range; anodic oxidation in 3% NaCl solution; composition of oxide films; strength of Ti—C bonds

We report on studies of the process of cyclic hydriding–dehydriding (eight cycles) of a mechanical alloy synthesized in a ball mill by grinding powder mixture Mg + 10 wt.% TiH2 + 10 wt.% Fe in argon medium. Hydrogen-sorption properties and thermal stability of the mechanical alloy are studied employing thermodesorption spectroscopy at hydrogen pressure of 0.1 MPa. Hydrogen capacity of the mechanical alloy is determined to be 4.9 wt.%, and onset temperature of hydrogen desorption from the alloy under this study equals 220°C. Kinetics of the process of hydrogen desorption from the hydride phases of the mechanical alloy is examined. The present studies have revealed that mechanical treatment of the magnesium powder in Ar medium with both Fe and Ti additives causes a greater effect on improving the kinetics of hydrogen desorption from hydride phase MgH2 of the alloy and decreasing its thermal stability in comparison with that caused by mechanical treatment of the same powder with either Fe or Ti additives in hydrogen medium.
Keywords: mechanical alloy; hydrogen-sorption properties; thermal stability; thermodesorption spectroscopy; reactive mechanical alloying

Industrial Electron-Beam Installation L-4 for Melting and Vacuum Refining of Metals and Alloys by N. I. Grechanyuk; P. P. Kucherenko; A. G. Mel’nik; I. N. Grechanyuk; Yu. A. Smashnyuk (489-495).
Electron-beam melting is the most effective method of refining and degassing metals in vacuum. Equipment for its implementation is produced in Germany, USA, Ukraine, and other countries. The paper discusses the design features and process capabilities of an industrial electron-beam installation of new generation for melting and vacuum refining of metals and alloys with an intermediate vessel or a direct crystallizer developed at the ELTECHMACH Research and Manufacturing Company (Vinnitsa, Ukraine). A distinctive feature of the installation is the ability to melt highly reactive and refractory metals and materials with a high gas content through the use of high-voltage glow discharge guns that operate steadily in relatively low vacuum.
Keywords: electron-beam installation; electron-beam melting; refining of metals and alloys; intermediate vessel; crystallizer; gas-discharge electron-beam gun

Magnetodielectrics Based on Magnetically Soft Materials. From Origins to Present by B. S. Baitalyuk; V. A. Maslyuk; S. B. Kotlyar; Ya. A. Sytnyk (496-503).
The paper presents a detailed review of magnetodielectric materials. Major types of magnetodielectrics are analyzed from their invention to present time. Production methods and basic properties of these magnetic materials are described. The focus is given to modern magnetodielectrics based on magnetically soft amorphous and nanocrystalline alloy powders. These magnetodielectrics display high saturation induction (about 1.5 T) and high temperature stability, making them major competitors for expensive permalloys.
Keywords: magnetically soft materials ; magnetodielectrics ; nanocrystalline alloys ; AlSiFe alloys ; permalloys ; carbonyl iron