Powder Metallurgy and Metal Ceramics (v.53, #9-10)

Mechanosynthesis of Nanodispersed Titanium Diboride by M. P. Saviak; A. B. Mel’nik; Yu. M. Solonin; A. V. Kotko; I. I. Timofeeva; I. V. Uvarova (497-504).
Structural and morphological changes of titanium during intensive milling of titanium and boron powder mixtures in an AIR-015M planetary-ball mill are investigated. It is shown that the structural transformations in titanium lead to the formation of cluster precipitates (like Guinier–Preston zones) of titanium and boron atoms that are regularly oriented with respect to the titanium lattice and coherently associated with it. Cluster precipitates are very effective nuclei for the further reaction and provide an explosive transition to the almost single-phase titanium diboride. It was found that, in the investigated mechanosynthesis conditions, nanostructured titanium diboride forms in the form of flat and spatial polycrystalline particles, composed of oriented nanograins no larger than 20 nm.
Keywords: mechanosynthesis; titanium diboride; structural transformation; nanostructure

Effect of the Parameters of Melt Dispersion Process on the Morphology, Structure, and Particle Size of Water-Atomized Aluminum Powders by O. D. Neikov; G. I. Vasil’eva; A. V. Samelyuk; V. G. Tokhtuev; V. A. Zhoga; E. A. Potipaka; I. I. Odokienko (505-513).
Water atomized powders of aluminum and aluminum alloys produced at a melt temperature of 690−1350°C and a water pressure of 2.0−16.0 MPa are studied. It is established that the melt temperature and the water pressure in these ranges hardly affect the shape of particles similar in size and their surface geometry. The particle size is a key parameter in the shaping and structure formation of particles. The heat transfer process occurs in film boiling conditions because of high temperature difference at 380−935°C and heat flux much higher than critical. It is established that the heat transfer coefficient at a water pressure of 10−14 MPa changes from 104 to 4 · 104 W/(m2 · °C) with a standard deviation of ±5.5% as the heat flux changes from 107 to 5 · 107 W/m2. This technique to determine the heat transfer coefficient involves the calculation of the cooling rate using the dendritic parameter, which allows increasing the accuracy of calculation.
Keywords: dispersion; melt; water pressure; heat exchange; cooling rate; film boiling; shaping of particles; particle size composition

Formation of Diborides of Groups IV–VI Transition Metals During Mechanochemical Synthesis by G. N. Makarenko; L. A. Krushinskaya; I. I. Timofeeva; V. E. Matsera; M. A. Vasil’kovskaya; I. V. Uvarova (514-521).
Fine powders of diborides of groups IV–VI transition metals (TiB2, HfB2, NbB2, TaB2, CrB2, Mo2B5, and W2B5) were produced by mechanochemical synthesis and low-temperature heat treatment of activated charges. The particle size of the powders was ≤1 μm. It is revealed that processes of formation of diborides of groups IV–VI transition metals differ within period and group. Diborides Ti and Nb formed discontinuously. Diborides Hf and Ta formed after the formation of lower boride phases, whereas higher borides Cr, Mo, and W formed in almost a single-phase state only after a low-temperature treatment of preliminarily mechanoactivated charges. The differences were analyzed from the point of view of the donor-acceptor capacity of the atoms of boron and diboride-forming transition metals.
Keywords: fine powder; diboride of transition metals; mechanochemical synthesis; donor-acceptor capability

Orbital Forging of Sintered Porous Billets by G. A. Baglyuk; V. G. Kurikhin; S. P. Gozhii (522-528).
Features of the deformation of sintered porous billets during orbital forging are considered. A schematic of an orbital forge with a roller as a punch is shown. To study orbital forging processes, cylindrical samples made of iron powder and its mixture with 1% of graphite compacted under 550, 700, and 850 MPa and sintered at 1150°C were used. The variation of the relative density and radial strain of billets during orbital forging with the axial strain and the variation of the strain with the shape factor of porous billets are described. It is shown that the total force of orbital forging is much lower (by a factor of 3.0–4.5) than the load needed to form similar billets by conventional free upsetting.
Keywords: orbital forging; porous billets; porosity; densification; local strain; plastic zone

The paper overviews experimental and theoretical studies focusing on the sintering of cermet and ceramic bodies conducted and published from 1922 to 1967. Special attention is paid to the generation and evolution of new ideas, elements of the physical theory of sintering, and attempts to use the entire wealth of knowledge in solid-state physics and physical mechanics available in a given time period. Analysis of the accumulated knowledge on sintering phenomena and the actual contribution of individual researchers to this process may promote further improvement of the physical theory of sintering and its advance to applied problems of powder materials. The key role of theoretical physicists, Frenkel, Herring, and Lifshits, in resolving the most complex problems of sintering science is emphasized.
Keywords: sintering; recrystallization; cohesion force; adhesion; sintering stages; viscous flow; diffusion of vacancies; growth of contacts; shrinkage; pore coalescence; porous body model; grain boundaries

Characterization of Ball Milled Ni–Al2O3 Nanocomposite Powders by Taib Muhammad Arif; Nouari Saheb (541-548).
Homogenous Ni–Al2O3 nanocomposite powders with uniform distribution of Al2O3 nanoparticles were obtained through ball milling of Ni and Al2O3 powders for 9 hours. Field emission scanning electron microscopy and X-ray mapping were used to characterize the ball milled powders and Al2O3 nanoparticles’ dispersion, respectively. The evolution of crystallite size and lattice strain in the nanostructured Ni powder was followed through X-ray diffraction. It was found that ball milling led not only to the uniform dispersion of the Al2O3 nanoparticles, but also to the reduction in crystallite size and increase in the lattice strain of the Ni phase. For the composite containing 5 wt.% Al2O3, the increase of milling time from 0 to 9 hours led to a continuous decrease of the crystallite size of the Ni phase from 1120 to 36 nm. For the composite containing 10 wt.% Al2O3, the increase of milling time from 0 to 2 hours augmented the lattice strain of the Ni phase and a further increase of milling time to 9 hours led to its decrease.
Keywords: nanoparticles dispersion; nanocomposite powders; ball milling; crystallite size; lattice strain

The Mechanical Properties of Compact Titanium Produced from Titanium Hydride Powders Using Self-Propagating High-Temperature Synthesis by A. I. Dekhtyar; O. M. Ivasishin; I. V. Moiseeva; V. K. Prokudina; D. G. Savvakin; A. E. Sychev (549-556).
The mechanical properties of titanium compacts from titanium hydride powders produced by conventional heat treatment of titanium sponge in hydrogen and by self-propagating high-temperature synthesis are compared. It is shown that the strength and plastic characteristics of titanium from powders hydrogenated by self-propagating high-temperature synthesis are not worse and sometimes even better than those of titanium produced in the same way from conventional hydride powders. It is determined that titanium sintered from powders hydrogenated by self-propagating high-temperature synthesis commonly contains more oxygen compared to titanium sintered from powders hydrogenated by heat treatment in hydrogen. However, titanium made of powders from self-propagating high-temperature synthesis contains a lower content of other impurities decreasing its plasticity. It is assumed that the yield stress, ultimate strength, and plastic characteristics of titanium sintered from powders produced by different methods are determined by the quantitative and qualitative composition of impurities.
Keywords: titanium hydride powder; self-propagating high-temperature synthesis; mechanical properties of titanium

In this work, the mechanical properties such as elastic moduli, shear moduli, and hardness of titanium–titanium boride composites with 20% and 40% of titanium boride reinforcements were estimated by ultrasonic and nanoindentation techniques. The estimated values obtained from the both measuring techniques are compared. The composites were processed by three powder metallurgical techniques such as spark plasma sintering, hot isostatic pressing, and vacuum sintering. The composites processed through spark plasma sintering and hot isostatic pressing showed better mechanical properties compared to the vacuum sintered composites. The effects of titanium boride reinforcements and their morphological influences on the mechanical properties are also described.
Keywords: ultrasonic and nanoindentation technique; titanium composites; mechanical properties

The structure and properties of biogenic hydroxyapatite ceramics for medical applications produced by microwave and conventional sintering at 800, 900, 1000, and 1100°C are studied. It is established that microwave sintering allows a 33 to 50% decrease in the minimum grain size, which can be attributed to the influence of microwaves on the material structure compared to conventional sintering. The bioceramic samples produced by microwave sintering have stable porosity (~40%) and 30–59 MPa compressive strength, being close to that of native bone and 1.6 to 2 times higher than the compressive strength of samples prepared by conventional sintering. In vitro studies have shown that the solubility of bioceramics sintered in a microwave oven in saline is 1.7 to 5.5 times higher than the solubility of samples produced by conventional sintering. Thus, microwave sintering allows obtaining biogenic hydroxyapatite ceramics with improved mechanical and biological properties for filling bone defects in orthopedics and traumatology.
Keywords: hydroxyapatite; biomaterial; microwave sintering; porosity; compressive strength; solubility

The Mechanical Properties of Sialon–Boron Nitride Composite Ceramics by I. P. Neshpor; T. V. Mosina; O. N. Grigoriev; A. D. Panasyuk; A. V. Koroteev; N. D. Bega; L. M. Melakh; I. Zalite; A. D. Kostenko; N. V. Boshitskaya (574-582).
The production of sialon and sialon–boron nitride composites using oxidized (up to ~15 wt.% O) Si3N4–18 wt.% AlN composite powders resulting from plasma chemical synthesis is studied. Hot pressing of these powders to nonporous state at 1620–1775°C is accompanied by the formation of composites consisting mainly of a mixture of β-sialon (z = 1.5–2) and o′-sialon. Boron nitride additions in an amount of up to 15 wt.% lead to the formation of composites that contain BN lamellar grains in the matrix of single-phase β-sialon (z = 1.5–2). The mechanical and tribological characteristics of the composites with micron and submicron grains are examined. It is observed that the dependence of scratch hardness on contact strength is almost linear for the sialon ceramics and sialon–boron nitride composites. The material is removed during machining through intensive brittle fracture. The introduction of boron nitride into sialon ceramics in an amount of more than 5% is accompanied by approximately a tenfold increase in the material removal in machining, making possible turning operations.
Keywords: plasma chemical synthesis of powder; composite; boron nitride; sialon; hardness; contact strength; wear; machinability

The Surface Morphology and Electrophysical Properties of Thick SnO2–Sb Films After Laser Processing by V. E. Shelud’ko; A. V. Paustovskii; B. M. Rud’; A. G. Gonchar; I. I. Timofeeva; A. A. Rogozinskaya; E. Ya. Tel’nikov; P. S. Smertenko; N. I. Anyakin; V. V. Kremenitskii; I. V. Zakharchenko (583-594).
The influence of laser pulses on the structure and electrophysical properties of resistive thick films based on the Sn0.9Sb0.1O2 solid solution is studied. Scanning electron microscopy, atomic force microscopy, and X-ray diffraction are used to examine the structure of resistive thick films and determine the distribution of Sn0.9Sb0.1O2 solid solution in surface layers and across the film. Exposure of thick resistive films to nano- and microsecond laser pulses changes their currentvoltage characteristics compared to samples subjected to millisecond pulses. The current-voltage characteristics become practically linear in the range from 1 to 10–11 V, thus allowing one to determine the optimum (α = 1) operating voltage range for resistors. The temperature coefficient of resistance depends on the length and energy of pulses.
Keywords: resistor; laser; atomic force microscopy; solid solution; secondary electrons; currentvoltage characteristic; temperature coefficient of resistance; thermal fields

The effect of preliminary shock-wave treatment of graphite on its subsequent transformations into dense modifications of carbon under high-temperature shock compression is studied. It is shown that this treatment leads to higher concentration of turbostratic stacking defects, increases the extent of lattice microdeformation along the c axis, and induces the formation of twins with three-dimensional configuration of C— bonds on twin boundaries. These defects significantly but differently influence the phase transformations. Turbostratic defects inhibit phase transformations whereas microdeformation and twins accelerate them.
Keywords: graphite; shock compression; structural effects; phase transformations

Developing New Design and Investigating Porous Nozzles for Abrasive Jet Machine by V. Sychuk; O. Zabolotnyi; A. McMillan (600-605).
The paper presents a new principle of improving the durability of a nozzle for abrasive jet machine. Results of the study on the manufactured porous element (a part of the new design of abrasive jet nozzle) were presented. Conversion of obtained 2D scan results into 3D with the purpose of computer modelling to simulate the air flow through a porous cylindrical insert was carried out.
Keywords: abrasive jet machine; nozzle; computer simulation; carbides; air layer; self-conducting high-temperature synthesis

Effect of Alternating Electrical Field and Ultrasound on Corrosion of Nanosized Copper Films by A. F. Andreeva; A. M. Kasumov; E. A. Potipaka; A. V. Musiichuk; N. A. Vlasenko; V. M. Karavaeva (606-609).
The paper examines the dependence of corrosion rate of nanosized copper films in an HCl aqueous solution on the frequency and strength of an alternating electrical field and ultrasound as well as the thickness of layers under these factors. The corrosion rate was evaluated from increase in the resistivity of films. It is shown that the corrosion rate decreases at least by one-fifth in the range of low strength (to 5 V/cm and 10 dB, respectively) and frequency (to 200 kHz). The corrosion slows down because ions of the solution participate in the oscillation process. This effect of alternating field and ultrasound can be used to control the corrosion rate of nanosized copper films in electronics and medicine. The influence of ultrasound is predominant for layers less than 100 nm in thickness since it decreases the high chemical activity of nanosized film islands.
Keywords: copper; film; corrosion; alternating field; ultrasound

The paper overviews the historical evolution of technologies and applications of copper, bronze, brass, and other copper-based alloys that were in use in the Bronze Age and found further development from the Middle to modern times.
Keywords: copper; bronze; brass; casting; bell metals; firearms; structural alloys; powder metallurgy; electrical alloys