Powder Metallurgy and Metal Ceramics (v.47, #7-8)

Effect of mechanical activation on the in situ synthesis of aluminosilicates in the BN-Al2O3-SiO2-Si3N4 system by L. R. Vishnyakov; A. V. Maznaya; T. V. Tomila; L. N. Pereselentseva (373-378).
The paper examines how mechanical activation influences the in-situ phase formation of aluminosilicates in the BN-Al2O3-SiO2-Si3N4 system. The major factor that influences the activation of the charge is the duration of high-energy machining. Results from infrared spectroscopy and data on the particle size and specific surface of the charge show that short-term (10–20 min) attritor grinding is sufficient to obtain a mixture and composite of high quality.
Keywords: composite material; boron nitride; aluminosilicates; mullite; mechanical activation; infrared spectroscopy; particle size

Low-temperature synthesis of α-Al2O3 by E. V. Dudnik; A. V. Shevchenko; A. K. Ruban; V. P. Red’ko; L. M. Lopato (379-383).
The paper considers the production of nanocrystalline α-Al2O3 powder at a temperature below 900 °C. It is shown that α-Al2O3 forms after high-temperature treatment of aluminum nitrate mixed with a mineralizer at 650 °C (holding time of 6 h). The primary particles of α-Al2O3 are 25 to 30 nm in size and the specific surface area is 15.2 m2/g. The powder is used to produce self-reinforced composites in the ZrO2-Y2O3-CeO2-Al2O3 system.
Keywords: alumina; nanocrystalline powder; ZrO2-Y2O3-CeO2-Al2O3 system; self-reinforced composite

Production of TiNi fibers by melt extraction by A. G. Kostronov; V. N. Klimenko; M. M. Serov; N. I. Levitskii; S. V. Prishchepov; B. V. Borisov (384-388).
The paper examines the production of TiNi fibers by pendent-drop melt extraction in vacuum. The mean effective diameter of the continuous fibers produced is 37 µm. Resistometrical investigation establishes that martensitic transformations in the fibers start at Ms = 17 °C.
Keywords: TiNi fiber; melt extraction; shape memory effect

The paper examines the possibility of producing porous sheets by rolling binary mixtures of ultrafine powders of nickel, copper, and cobalt. The effect of the rolling rate on the thickness and porosity of sheets and on the specific surface area of powders after rolling is studied. The best rollability is shown by nickel and copper powders and by powders produced from mechanical mixtures of formates.
Keywords: ultrafine powders; rolling; binary mixtures; rolled sheets; thickness; porosity

The purpose of this paper is to determine the apparent yield stress for P/M materials. Three kinds of materials are considered: pure iron, copper, and aluminum. The models of loading functions for porous materials are recalled. The experimental results solve identification problems for the yield parameters of the above P/M materials.
Keywords: iron; copper; aluminum; powder metallurgy; apparent yield stress; cold forming

The paper examines the high-temperature interaction between powder solid solution of carbon in β-SiC and powder titanium hydride. The structure of the composite materials sintered from the synthesized products and titanium matrix is studied. It is established that the composite alloy has high mechanical characteristics.
Keywords: solid solution of carbon in β-SiC; titanium hydride; eutectic; powder master alloy; cathode-ray remelting plant; composite alloy

There are numerous methods for preparing copper nanoparticles of which electrodeposition is one of the most suitable and simplest. The electrolyte used in the present investigation is an acidified aqueous solution of copper sulphate with suitable additives. By varying the input dc voltage with a constant current, a spongy layer of copper particles is deposited on the cathode surface. Particles are collected and characterized by XRD and UV-Vis, the surface morphological characterization is done by SEM and TEM.
Keywords: copper nanoparticles; electrodeposition; spongy layer; transmission electron microscopy; scanning electron microscopy; XRD; UV-VIS

Mechanical properties of powder titanium at different production stages. I. Densification curves for titanium powder billets by E. M. Borisovskaya; V. A. Nazarenko; Yu. N. Podrezov; O. S. Koryak; Ya. I. Evich; V. F. Gorban’ (406-413).
The mechanical behavior of titanium powder billets at all production stages is examined. The dependence of how mechanical properties are formed on the structure is established. The compaction of a powder pressed in a rigid die mold, which is the initial stage of the production process, is analyzed. The experimental dependence of the compacting force on porosity is examined. The results are compared with theoretical data available.
Keywords: powder titanium; mechanical properties; strain hardening

Production and properties of copper-based compacts by L. A. Ryabicheva; A. T. Tsyrkin; A. P. Sklyar (414-419).
The paper describes the production of copper from fibrous charge, including pressing, hot forging at 900 °C, and subsequent cold deformation along the billet axis. Changes in density, strength, and plasticity are studied. Copper produced with this process meets standard requirements for cast and deformed rods. The process proposed includes fewer operations and requires less energy than the conventional recycling of scrap to obtain copper (remelting, refining, and metal forming).
Keywords: copper; fibrous charge; hot pressing; fiber length; fiber diameter; density; strength; plasticity

The solidus surface for the Al2O3-ZrO2-Yb2O3 phase diagram is plotted onto the concentration triangle for the first time. It consists of four isothermal three-phase fields that correspond to two invariant eutectic equilibria and two invariant peritectic equilibria. The solidus surface also includes five ruled surfaces representing the end of crystallization in binary eutectics. The highest solidus temperature in the system is 2710 °C, which is the melting temperature for pure ZrO2, while the lowest temperature is 1765 °C, which is the melting temperature for the AL+F+Yb3A5 ternary eutectic. No ternary compounds or noticeable areas of solid solutions based on components and binary compounds are found in the ternary system. The phase equilibrium diagram and reaction scheme for the equilibrium crystallization of Al2O3-ZrO2-Yb2O3 alloys are plotted using data on bounding binary systems and liquidus and solidus surfaces.
Keywords: zirconia; alumina; ytterbia; interaction; solidus surface; phase equilibrium diagram; crystallization scheme; phase diagram

Thermodynamic assessment of the Cu-Ti-Zr system. II. Cu-Zr and Ti-Zr systems by M. A. Turchanin; P. G. Agraval; A. R. Abdulov (428-446).
The thermodynamic assessment of the Cu-Zr and Ti-Zr systems is carried out using the CALPHAD method. The Gibbs energy of Cu-Zr liquid alloys is described by the ideal associated solution model. The excess Gibbs energy of Ti-Zr liquid alloys and Cu-Zr and Ti-Zr solid solutions is descried by models with Redlich-Kister polynomials. The Gibbs energy of Cu-Zr intermetallic compounds is described by models taking into account their formation enthalpy and entropy. A set of self-consistent parameters of the models is obtained using data on phase equilibria and thermodynamic properties of the phases. The calculated phase diagrams of the systems and values of thermodynamic properties of the phases are in good agreement with experimental information. The relative thermodynamic stability of supercooled liquid alloys and competitive crystal phases of the Cu-Zr system are analyzed.
Keywords: phase diagram; thermodynamics; thermodynamic modeling; copper-zirconium alloys; titanium-zirconium alloys

Interaction of niobium and iron with stibium by Ya. F. Lomnitska (447-450).
The interaction between components in the Nb-Fe-Sb system is examined with x-ray diffraction. An isothermal section of the phase diagram is plotted at 870 K up to 0.70 Sb mole fractions. The crystal structure is calculated using the powder method to confirm the existence of the Nb-Fe-Sb ternary compound with LiAlSi-type structure. Other ternary compounds are not found in the system.
Keywords: phase diagram; crystal structure; niobium; iron; stibium

Thermodynamic properties of holmium monogermanide by N. P. Gorbachuk; V. R. Sidorko; S. N. Kirienko; I. M. Obushenko (451-456).
The heat capacity and enthalpy of HoGe is investigated for the first time over a temperature range between 51.62 and 2096 K. The values of heat capacity, entropy, reduced Gibbs energy (J · mole−1 × × K−1), and enthalpy (J · mole−1) are determined at 298.15 K: C °P(T) = 49.63 ± 0.20; S °(T) = 89.1 ± 0.7; Φ′(T) = 50.9 ± 0.8; H °(T) − H °(0 K) = 11391 ± 57. Temperature dependences of enthalpy (J · mole−1) for holmium monogermanide are determined as follows: H °(T) − H °(298.15 K) = 8.474 × × 10−3 · T2 + 47.13 · T + 226747 · T−1 − 15565 and H °(T) − H °(298.15 K) = 88.91 · T − 26507, for 298.15–1765 K and 1951–2096 K, respectively. The enthalpy and entropy of HoGe melting are calculated: Tm = 1765 ± 35 K, ΔHm = 36.3 ± 2.9 kJ · mole−1, ΔSm = 20.5 ± 1.6 J · mole−1 · K−1.
Keywords: thermodynamics; heat capacity; enthalpy; entropy; reduced Gibbs energy; germanide

The paper presents a thermodynamic analysis of chemical equilibrium in Co-Cr-Ni-Mo alloys with different chromium content (10, 20, and 30%) produced by point-source diffusion saturation under 0.1 MPa at 500–1500 K. The elements of the alloys are most likely transported by lower chloride molecules participating in cyclic reactions. The limiting concentration of chromium above which no changes occur in either gaseous or condensed phase is 20%. It is experimentally established that chromium rapidly diffuses into the cobalt base, accompanied by the formation of homogeneous alloy powders, under the actual nonequilibrium conditions for the production of cobalt alloy powders containing more than 20% of chromium.
Keywords: thermodynamic analysis; equilibrium; temperature; alloy; composition; compound; gas; concentration; cyclic reaction

Thermodynamic properties of Ge-Y alloys and binary systems of germanium with transition metals by V. S. Sudavtsova; N. I. Usenko; T. M. Zinevich (461-465).
The partial (for yttrium) mixing enthalpies of Ge-Y melts are determined using high-temperature isoperibolic calorimetry at 1780 ± 5 over a concentration range 0 < xY < 0.4. These data are used to calculate the integral mixing enthalpy of the melts. The formation of Ge-Y alloys is accompanied by substantial exothermic effects. The ΔH values for Ge-Y liquid alloys are generalized on the basis of our and literature data. The activities of the components of Ge-Y melts are calculated using the liquidus coordinates of the Ge-Y phase diagram. The values obtained are characterized by very large negative deviations from the Raoult law. The thermochemical properties of Ge-3d-Me melts, dimensional and electrochemical factors, and the occupation of the valence d-orbitals of transition metals are analyzed.
Keywords: calorimetry; enthalpies of mixing and formation; binary systems; melts; yttrium; germanium; d-metals

The enthalpy of the La3Se4 and La2Se3 boundary compositions of the La3−xSe4 phase (0 ≤ x ≤ 1/3) at temperatures from 370 to 2260 K is studied calorimetrically. The values obtained are used and the equilibria of the La-Se system are analyzed to establish, for the first time, the temperature-concentration relationships for the thermodynamic properties of La3−xSe4 selenides in the homogeneity region at 298 K ≤ T ≤ 2123 K. The enthalpy function (J/mole) of La3−xSe4 is given by H(T) − (298 K) = (3837 · 103T−1 − 85852 + 266.925 · T − 8.7503 · 10−2 T2 + 3.437 · 10−5 T3) · e−0.2869x. The formation and melting enthalpies of La3Se4 are determined: ΔfH °(298 K) = −1340 ± ± 28 kJ/mole), ΔmH = 147.5 ± 9.6 kJ/mole. It is shown that the high-temperature stability of different La3−xSe4 compositions is strongly dependent on pressure: as pressure decreases and temperature increases, the selenium content is reduced and the composition tends to La3Se4.
Keywords: thermodynamic properties; heat capacity; enthalpy; formation enthalpy; entropy; Gibbs energy; lanthanum selenides; homogeneity region

Potentiodynamic cycling is proposed to select conditions for the activation of zirconium-alloy electrodes of a nickel-hydride accumulator. The electrochemical characteristics of the electrodes are studied. It is shown that the full charge and discharge capacities are impossible in hydrogenation-dehydrogenation conditions that do not correspond to the polarization curves. The maximum discharge capacity under the same conditions is achieved for an electrode of 0.5 g while incomplete discharge capacity is observed for a sample of 0.1 g.
Keywords: polarization curves; hydrogenation; dehydrogenation; potentiodynamic cycling; activation of electrodes; hydrogen storage capacity

Mechanical-indentation analysis of the microstructure and properties of plasma-sprayed ZrO2-based coatings by V. Yu. Oliker; A. A. Pritulyak; V. F. Gorban’; V. L. Sirovatka (477-481).
The relationship between the mechanical properties of plasma-sprayed thermal-barrier coatings and the properties of feedstock powders is studied. These powders have the same chemical composition and are obtained by hydroxide coprecipitation followed by air-drying and by a cryochemical method. Information on TBC failure mechanisms is used to pose and solve the problem of increasing the plasticity and, consequently, the stress relaxation coefficient of the ceramic coating. The finer structure of the cryochemical powder sprayed coating also improves its crack-resistance. The minor reduction in the hardness of the cryopowder-sprayed coating should not deteriorate the performance of the thermal-barrier coating.
Keywords: thermal-barrier coatings; microstructure; hardness; plasticity; crack resistance

The paper examines the wear rate in friction of copper-impregnated samples produced by pressing of VK6 powder with chromium additions. The test is conducted on a cast iron disk in the presence of a wet SiC powder and on a diamond wheel without cooling. It is shown that higher chromium content insignificantly increases the sample wear rate in friction with the cast iron disk. At the same time, the wear rate abruptly decreases for the diamond wheel. The hardness of the samples does not significantly change with increasing chromium content to 6 wt.%.
Keywords: wear rate; friction; drill bits

The paper examines the advanced method of spark erosion for recycling hard-alloy scrap. It is shown that spark discharge over hard alloy in water leads to the decarburization of the initial WC phase in the surface layer and of the powder formed. After carburization, the powder can be used for the production of hard alloys. The structure and mechanical characteristics of the hard alloy made of the powder are studied.
Keywords: tungsten; cobalt; hard alloy; scrap; spark erosion

The structure and properties of the surface layers of metals and coatings in the initial state and after friction contact are examined. Substantial increase in the hardness of surface layers after friction is mainly associated with the formation of nanostructure due to shear strains. Deformation does not noticeably change the properties of surface layers when the nanostructure has been formed in the initial material. The relationship is established between the wear resistance and the following properties of the initial coatings and secondary structures: plasticity, stress relaxation coefficient, and their structural component.
Keywords: coating; deformation; secondary structures; hardness; plasticity characteristic; stress relaxation coefficient; wear resistance

Solid-state laser fusion of spherical titanium powders by K. E. Belyavin; D. V. Min’ko; O. O. Kuznechik; R. P. Bykov; D. A. Zatyagin (500-504).
The paper describes the selective laser fusion of spherical titanium powders with a titanium base in which solid-state (YAG: Nd3+) laser is used as a radiation source. Metallographic data on single-layer coatings of spherical titanium powders show that the liquid-phase formation of metal contacts resulting from the surface fusion of powder particles underlies the mechanism of selective laser sintering of porous materials.
Keywords: titanium; spherical powder; solid-state laser; coating; selective laser fusion