Powder Metallurgy and Metal Ceramics (v.48, #11-12)

A thermodynamic calculation is performed for processes occurring in the Fe–O–C–H system during decomposition–reduction of iron oxalate in a gaseous medium formed in the thermal destruction of high-molecular hydrocarbons. This makes it possible to choose optimal temperature conditions and ratios of components for obtaining magnetic iron-based powders for medicine with required phase composition. It is shown that, under the actual kinetic experimental conditions, the products of decomposition–reduction of iron oxalate in a complex gaseous medium are thermodynamically favored phases.
Keywords: thermodynamics of process; iron oxalate; complex gaseous medium; high-molecular hydrocarbons

Effect of gas media on the structural evolution and phase composition of detonation coatings sprayed from mechanically alloyed Ti–Al–B powders by V. E. Oliker; V. L. Sirovatka; T. Ya. Gridasova; I. I. Timofeeva; E. F. Grechishkin; M. S. Yakovleva; E. N. Eliseeva (620-626).
The paper examines the phase formation of detonation coatings sprayed from mechanically alloyed Ti–50 Al–25 B powder. It is shown that coatings with different phase compositions and functional properties can be consolidated from this activated powder by varying process conditions (including gas composition during detonation spraying). Three types of composite coatings with different structures are obtained: TiB and TiB2 inclusions are distributed in an intermetallic matrix (Al3Ti, γ-TiAl); inclusions of oxides and oxynitrides are additionally present in the same structure; inclusions of borides, Al, and Ti are distributed in a mixture of intermetallic and nitride (TiN, AlN) phases.
Keywords: detonation coating; Ti–Al–B powder; phase formation

Surface modification of silicon nitride nanofibers with titanium nitride particles by N. I. Tishchenko; V. G. Kolesnichenko; N. V. Dubovitskaya; P. M. Silenko; N. I. Danilenko; O. B. Zgalat-Lozinskii; V. N. Bulanov; A. V. Ragulya (627-633).
Silicon nitride nanofibers coated with titanium nitride particles are formed by deposition of TiO(OH)2 and Ti(O)2(OH)2 using controlled hydrolysis of TiCl4 followed by nitriding in an NH3 flow. The nitriding at 700–900°C permits the formation of 5 to 15 nm titanium nitride particles. The amorphous layer on Si3N4 fibers limits the nucleation of titanium nitride and thus the formation of continuous coatings. Titanium peroxyhydroxide Ti(O)2(OH)2 as a precursor is preferable for depositing titanium nitride coatings on silicon nitride fibers.
Keywords: nanofibers; nanoparticles; nanocomposite; Si3N4 and TiN nitrides

In this research, we demonstrate rapid mechanochemical synthesis of nanocrystalline α-alumina (α-Al2O3) from a starting mixture of hematite (Fe2O3) and aluminum (Al). The formation of α-Al2O3 nanocrystallites occurs during the solid-state reaction and through the reduction treatment. Also in this paper, effects of milling time on the particle size and lattice strain of nanocrystalline α-Al2O3 are investigated. The results indicate that complete reduction is reached only after 2 h of milling in a planetary mill and the crystallite size of obtained α-Al2O3 is in general about 12 nm. Also, it is found that increasing the milling time can effectively decrease the nanocrystalline size and increase the lattice strain of α-Al2O3. Finally, the experimental results show appropriate homogeneity and dispersion of related nanocrystallites.
Keywords: nanostructures; solid-state synthesis; scanning electron microscopy; transmission electron microscopy; X-ray diffraction

The objective of the work is to synthesize nanostructured FeAl alloy powder by mechanical alloying (MEA). The work concentrates on the synthesis, characterization, and structural and mechanical properties of the alloy. Nanostructured FeAl intermetallics are prepared directly by MEA in a highenergy ball mill. Milling is performed under toluene solution to avoid contamination from the milling media and atmosphere. Mixtures of elemental Fe and Al are progressively transformed into a partially disordered solid solution with an average composition of Fe–50 at.% Al. Phase transformation, structural changes, morphology, particle size measurement, and chemical composition during MEA are investigated by X ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS). Vickers microhardness (VMH) indentation tests are performed on the powders. The XRD and SEM studies reveal the alloying of elemental powders as well as transition to nanostructured alloy; crystallite size of 18 nm is obtained after 28 h of milling. Expansion/contraction in lattice parameter accompanied by reduction in crystallite size occurs during transition to nanostructured alloy. Longer milling introduces ordering in the alloyed powders as proved by the presence of superlattice reflection. Elemental and alloyed phases coexist while hardness increases during MEA.
Keywords: nanostructured powder; mechanical alloying; FeAl; disorder; ordering; ball milling

Mechanical properties of powder titanium at different production stages. V. Properties of a titanium strip produced by powder rolling by K. A. Gogaev; V. A. Nazarenko; V. A. Voropaev; Yu. N. Podrezov; D. G. Verbilo; O. S. Koryak; I. Yu. Okun (652-658).
A method for producing strips by titanium powder rolling is proposed. The effect from powder annealing on the porosity of the initial billet is analyzed. The optimal temperatures of sintering and annealing after intermediate rolling are determined. It is shown that, under the optimal deformation conditions, the strip has mechanical properties that compare well with those of strips produced conventionally.
Keywords: titanium powder; rolling; sintering; annealing; strength; plasticity; quality of contact

The paper examines the effect of ambient temperature, pressure, and nature, treatment purity, and oxidation of different metals on the tear strength of metal–fluoroplastic (pure and reinforced) surfaces. It is established that both pure and reinforced fluoroplastic shows strong adhesion to different metal surfaces at temperatures higher than the melting temperature of fluoroplastic and close to its sintering temperature. Fluoroplastic materials have lower wear resistance at high sliding speeds when high temperature is generated in the friction area since adhesion of fluoroplastic to the counterface surface substantially increases.
Keywords: adhesion; composite; wear resistance; sliding speed; temperature

Effect of compaction conditions on the properties of magnetically soft materials sintered from iron powder by G. A. Baglyuk; O. A. Panasyuk; O. V. Vlasova; V. Ya. Kurovskii (663-666).
The effect of compaction on the porosity and magnetic properties of materials sintered from iron powder is studied. It is shown that porosity, when it is more than 6.5%, is the major factor that determines the magnetic flux density of the material. With lower porosity, the magnetic properties are greatly influenced by another structural factor—strain accumulated during additional compaction.
Keywords: magnetically soft material; iron powder; magnetic flux density; deformation; porosity

Some features of processes for producing functional ceramics (piezomaterials and ferrites) are reviewed. Methods to optimize individual process stages and processes as a whole are proposed.
Keywords: piezoceramics; ferrites; structure; composition; process; pressing; sintering; nonstoichiometry; properties

Mixing enthalpies of liquid alloys and thermodynamic assessment of the Cu–Fe–Ni system by M. A. Turchanin; T. Ya. Velikanova; L. A. Dreval’; A. R. Abdulov; P. G. Agraval (672-692).
The partial mixing enthalpy of nickel in ternary liquid alloys of the Cu–Fe–Ni system is studied by the calorimetric method at 1873 K and xNi = 0–0.55. The $$ Delta {overline H_{Ni}} $$ function has mainly negative values over the composition range of interest. The results show the key role of binary interactions in the formation energetics of liquid alloys in the Cu–Fe–Ni system. A set of self-consistent parameters of thermodynamic models of the phases is obtained taking into account experimental data on the thermodynamic properties of liquid and solid solutions and data on stable phase transformations. The thermodynamic assessment of the system is carried out in the framework of the CALPHAD method. The calculated liquidus surface and isothermal and vertical sections of the phase diagram are in satisfactory agreement with corresponding experimental data. The metastable miscibility gap of supercooled liquid alloys in the Cu–Fe–Ni system is calculated.
Keywords: calorimetry; mixing enthalpy; thermodynamic properties; thermodynamic modeling; phase diagram; alloys of the Cu–Fe–Ni system

The Al2O3–HfO2–Y2O3 phase diagram. II. Liquidus surface by S. M. Lakiza; Ya. S. Tishchenko; A. O. Sus; Z. O. Zaitseva; L. M. Lopato (693-699).
The liquidus surface on the Al2O3–HfO2–Y2O3 phase diagram is constructed for the first time. No ternary compounds and appreciable solid solution regions based on components and binary compounds are found in the ternary system. The liquidus surface is completed by eight primary crystallization fields. Four four-phase invariant eutectic equilibria, one four-phase invariant transformation equilibrium, and three three-phase invariant eutectic equilibria are found. Since HfO2 interacts with other phases eutectically, the materials combine the unique properties of HfO2-based T and F phases with the properties of other phases in the Al2O3–HfO2–Y2O3 system.
Keywords: ceramics; hafnia; alumina; yttria; interaction; liquidus surface; phase diagram; eutectic materials

The paper examines the effect of scandium and yttrium additions (up to 5 and 10 at.%, respectively) on martensitic transformations and shape memory effect in TiNi. The martensitic temperature decreases differently in quenched TiNi-ScNi and TiNi-YNi alloys. The martensitic temperature dependence on scandium concentration is linear, and doping TiNi alloy with yttrium smoothly decreases the temperature to about 30°C at 10 at.% yttrium. The martensitic transformations in both systems are accompanied by the 100% shape memory effect. When titanium is replaced by a small amount of scandium (0.01 at.%.), the nature and parameters of martensitic transformation remain unchanged.
Keywords: scandium; yttrium; martensitic transformation; shape memory effect

Effect of phosphorus on the structure and properties of iron hemiboride in Fe–B–P alloys by I. M. Spiridonova; O. V. Sukhova; N. V. Karpenko (707-711).
The iron corner of the Fe–B–P phase diagram is plotted for room temperature based on metallographic and x-ray analyses. The structure and properties of phosphorus-doped iron hemiboride in Fe–3.8 wt.% B alloys containing 0 to 5 wt.% P are examined.
Keywords: phase diagram; iron hemiboride; iron phosphide; eutectic; micromechanical properties; oxidation resistance

Structural analysis of Zn2TiO4 doped with MgO by M. V. Nikolic; N. Obradovic; K. M. Paraskevopoulos; T. T. Zorba; S. M. Savic; M. M. Ristic (712-717).
The starting mixtures of ZnO, TiO2, and MgO (0, 1.25, and 2.5 wt.%) powders are mechanically activated in a high-energy planetary mill for 15 min and then sintered between 800 and 1100°C for 2 h. The influence of MgO addition on the structure of the samples obtained is analyzed with X-ray diffraction and infrared reflection spectroscopy. Room-temperature far-infrared reflectivity spectra of the samples doped with MgO (0, 1.25, and 2.5 wt.%) and sintered at 1100°C in the frequency range between 100 and 1200 cm–1 are measured and analyzed. Optical parameters are determined for seven oscillators belonging to the spinel structure using the four-parameter model of coupled oscillators. Born effective charges are calculated from the transversal/longitudinal splitting.
Keywords: zinc titanate; magnesium oxide; powders; sintering; mechanical activation; X-ray diffraction; infrared reflection spectroscopy; structure

Copper tungstate produced from tungsten-containing waste as addition to antifriction material by A. G. Kostornov; V. V. Pasichnyi; O. I. Fushchich; V. T. Varchenko; V. S. Korchemnaya (718-722).
The paper examines the use of tungsten-containing waste to develop a copper-based microheterogeneous antifriction material. The effect of copper tungstate CuWO4 on the tribotechnical properties of antifriction material Cu–Sn–CuWO4–MoS2 is analyzed at a pressure between 1.25 and 17.5 MPa and sliding speeds of 0.5 and 1.0 m/sec with liquid lubrication. It is established that the composite antifriction material Cu–Sn–CuWO4–MoS2 can perform up to 17.5 MPa at a sliding speed of 0.5 m/sec and up to 12.5 MPa at 1 m/sec. The antifriction composite Cu–9 Sn–7.5 CuWO4–5 MoS2 has the optimal friction coefficient (0.135–0.01) and wear (6.0–3.1 μm/km) between 1.25–12.5 MPa under the above conditions and can perform up to 150°C. When Cu–Sn–CuWO4–MoS2 is sintered in hydrogen, CuWO4 decomposes and reduces to pure metal, and tungsten particles reinforce the matrix. The antifriction material Cu–Sn–CuWO4–MoS2 is microheterogeneous. The load-bearing component (matrix) represents an α-solid solution of tin in copper. Fine tungsten particles that are uniformly distributed in the matrix reinforce it and improve the bearing capacity of the material. Inclusions of molybdenum disulphide contribute to the formation of secondary structures on the friction surface and decrease the friction coefficient.
Keywords: copper; tungsten; tin; copper-based composite antifriction material; alloying elements; strengthening; microheterogeneous structure; pressure; sliding speed; temperature; friction coefficient; wear

The paper examines the effect of the tube diameter and powder weight flow rate on the critical gas velocity and associated pressure difference when such materials are transported through horizontal tubes. Dependences needed to design and construct pneumatic transport facilities are obtained.
Keywords: particulate materials; pneumatic transport; critical flow velocity

Chemical treatment of cubic boron nitride grinding powders to remove admixtures by G. P. Bogatyreva; G. D. Ilnitskaya; A. N. Sokolov; G. F. Nevstruev; O. V. Leshchenko (726-729).
The paper examines the chemical and thermochemical treatment of cubic boron nitride (cBN) grinding powders with solutions of mineral acids and alkalis (sodium and potassium hydroxides) with different concentrations. In addition, cBN grains are treated with a sodium hydroxide melt at 350 to 700°C for 1 h. It is established that treatment with solutions of mineral acids and alkalis with different concentrations, even for a long time, has no effect on the decomposition of cBN grains. The cBN grains decompose under the action of sodium hydroxide melt and release ammonia. With increasing treatment temperature, the decomposition of cBN grains is intensified.
Keywords: cubic boron nitride; grains; grinding powders; chemical treatment; thermochemical treatment