Powder Metallurgy and Metal Ceramics (v.49, #1-2)

Formation of copper deposits under electrolysis with surface-active agents by I. B. Murashova; N. E. Agarova; A. B. Darintseva; A. B. Lebed; L. M. Yakovleva (1-7).
The growth of dendritic deposit under galvanostatic electrolysis is modeled and a method is developed to analyze its formation in laboratory. The time dependences for cathodic overpotential are plotted and the rod electrode with deposit is video-recorded to establish that copper dendrites form at smaller tip-radius density from the solution with surface-active agent F2 than from the solution without additions. This results in higher fluidity of the powder. Nevertheless, dendrites formed from the solution with F2 addition have greater tip radii than the deposit from the pure solution. In addition, the dendritic deposit intensively grows for a longer time with F2 addition, thus increasing the yield of powder and decreasing the yield of cathodic scrap. The results from the laboratory experiment have been confirmed by commercial production.
Keywords: electrolytic copper powder; galvanostatic electrolysis; surface-active agent; growth dynamics; deposit structure

The paper studies the interrelation between the effective elastic properties and the size of contact areas in the unit cell in modeling a unidirectional hexagonal fiber strand under isostatic and uniaxial pressing in a plastic flow. For a range of relative densities (0.907–1), it is shown that effective Young’s modulus and Poisson’s ratio correlate well with the integral projection of the contact areas relative to the corresponding cell size. For pore channels with cross-sectional shapes close to a three-beam hypocycloid with unequal beams, the elastic properties in the plane perpendicular to the fiber axis are anisotropic because the cross-sectional projections of the pore channel have different sizes.
Keywords: unidirectional fibers; effective elastic properties; contact area width; pore channel; starlike crack

Sintering stability of biporous materials under kinematic constraints by M. B. Shtern; A. V. Kuz’mov; V. V. Skorokhod; E. Olevskii (17-23).
The behavior of porous materials with bimodal pore distribution under external loads and kinematic constraints is considered. Numerical methods of continuum mechanics of sintering are used. The effect of partial and complete constraining of the surface bounding the billets in sintering is studied. Corresponding distributions of small and large pores are determined. The sensitivity of the distributions to constraining/loading paths is established.
Keywords: constrained sintering; bimodal pore size distribution; rheological constitutive equations

A new approach is proposed to model the sintering of inhomogeneous macroscopic powder bodies. Each macroscopic element has a corresponding representative cell defined at the mesoscopic level of powder particles. Numerical modeling is carried out both at the level of representative cells and macroscopic level. The new approach does not use macroscopic constitutive equations in analytical form but rather derive them by homogenization over the representative cells. Thus, the number of internal parameters in sintering models can be increased and the effect of other parameters such as pore size distribution and anisotropy on sintering kinetics can be considered. Free sintering of ceramic matrix composites with coarse inert inclusions is modeled as an example. It is shown that the results of modeling and experiment agree if shear-induced dilatation of ceramic matrix powder during sintering is assumed.
Keywords: diffusion sintering; multiscale modeling

Effects of microwave heating in nanostructured ceramic materials by Yu. V. Bykov; S. V. Egorov; A. G. Eremeev; V. V. Kholoptsev; I. V. Plotnikov; K. I. Rybakov; V. E. Semenov; A. A. Sorokin (31-41).
This paper studies the influence of microwave heating on mass transport phenomena and phase transformations in nanostructured ceramic materials. Faster mass transport that depends significantly on the microwave field intensity is observed during microwave annealing of nanoporous alumina membranes. The effect of the microwave field on phase transformations and pore structure evolution in alumina powder compacts is characterized quantitatively. Preferred orientation of pores in ceramics sintered under linearly polarized microwave radiation is predicted theoretically and demonstrated experimentally. Decrease in the activation energy of plastic deformation is experimentally observed for alumina-based ceramics under microwave heating.
Keywords: microwave processing of materials; nonthermal microwave effects; gyrotron; nanoceramics; nanostructured materials

Sintering of self-reinforced ceramics in the ZrO2–Y2O3–CeO2–Al2O3 system by A. V. Shevchenko; E. V. Dudnik; A. K. Ruban; V. P. Red’ko; L. M. Lopato (42-49).
The formation of self-reinforced composites in the ZrO2–Y2O3–CeO2–Al2O3 system is investigated. Depending on different sintering conditions, plates of CeAlO3, T-ZrO2, and α-Al2O3 are formed in the matrix based on a solid solution of ZrO2. The self-reinforced composite with fracture toughness 17–20 MPa ⋅ m0.5 is obtained in optimum sintering conditions. In this composite, α-Al2O3 plates as well as individual Ce2O3 ⋅ 11Al2O3 plates are arranged in the matrix based on T-ZrO2. Selfreinforced composites in the ZrO2–Y2O3–CeO2–Al2O3 system have a considerable potential for various engineering ceramic materials with tailored combinations of properties, e.g., for medical applications (surgical tools and bioinert implants).
Keywords: ZrO2–Y2O3–CeO2–Al2O3 system; self-reinforcing; sintering; α-Al2O3 plate; zirconia

Thermal stability of nanosized composite C–Cu films by A. A. Onoprienko; N. I. Danilenko (50-54).
The behavior of composite C–Cu–C film, which is deposited by dc magnetron sputtering and in which nanosized copper particles are located between two layers of amorphous carbon, is studied during annealing at 600°C in vacuum. The structural evolution is examined by transmission electron microscopy and electron diffraction. The structure of the composite film is found to be stable in annealing up to 15 h. The diffusion coalescence of copper particles is greatly restricted by the specific microstructure of carbon matrix.
Keywords: amorphous carbon; film; structure; diffusion coalescence; transmission electron microscopy; electron diffraction

Spark-deposited coatings on magnesium alloys by I. A. Podchernyaeva; A. D. Panasyuk; D. V. Yurechko; V. N. Talash (55-60).
The paper examines the mass transfer kinetics, structure, and properties of spark-deposited coatings on magnesium alloys. They are obtained using composite ceramic electrodes in the AlN–Zr(Ti)B2 and B6Si–CaB6 systems. It is revealed that the microhardness and corrosion resistance of the coatings increase in a 3% NaCl solution and the abrasive wear decreases as compared with uncoated magnesium alloy.
Keywords: electrospark deposition; ceramic coatings; magnesium alloys; wear resistance

Abrasive wear resistance of detonation coatings from mechanochemically alloyed Ti–Al–B powders by V. E. Oliker; V. L. Sirovatka; E. F. Grechishkin; T. Ya. Gridasova (61-65).
The paper examines the abrasive wear resistance of composite detonation coatings with different structures based on Ti–Al–B, Ti–Al–B–O, and Ti–Al–B–N systems. It is established that the coating consisting of an intermetallic matrix and solid-phase inclusions as titanium borides and oxides has the highest characteristics. The coating whose microstructure is based on a random two-phase mixture of relatively soft intermetallic and nitride phases and whose hard component is represented only by borides has the lowest wear resistance.
Keywords: coatings; structure; borides; oxides; intermetallic

Structurization of (AlN–TiN)–(Ni–Cr)–(TiN–Cr3C2) composite ceramics under concentrated solar radiation by V. G. Kayuk; O. N. Grigor’ev; A. D. Panasyuk; T. V. Mosina (66-70).
A complex oxide film forms when (AlN–TiN)–(Ni–Cr)–(TiN–Cr3C2) composite ceramics are exposed to concentrated solar radiation. The film has good adhesion to the base and contains oxide phases which show chemical affinity to one another and form solid solutions. This film is continuous and protects the composite against further oxidation.
Keywords: microstructure; surface layers; concentrated solar radiation; solid solutions; metal sublayer; oxides; microhardness

The solidus surface for the Al2O3–HfO2–Y2O3 phase diagram is constructed for the first time. It consists of five isothermal fields, which correspond to four invariant eutectic equilibria and one invariant transformation equilibrium. The solidus surface includes also six ruled surfaces of binary eutectic crystallization end and T + F co-crystallization end. The highest solidus temperature in the system is 2810°C (HfO2 melting point) and the lowest is 1755°C (ternary eutectic AL + F + Y3A5 melting temperature). No ternary compounds or appreciable solubility of the third component in binary compounds and components are found in the ternary system. The phase equilibria diagram and reaction scheme for equilibrium crystallization of Al2O3–HfO2–Y2O3 alloys are constructed using data on the bounding binary systems and liquidus and solidus surfaces.
Keywords: hafnia; alumina; yttria; interaction; solidus surface; phase equilibria diagram; crystallization scheme; phase diagram

The Al–Cu–Ir isothermal section at 800°C in the aluminum-rich range by D. O. Kapush; B. Grushko; T. Ya. Velikanova (79-85).
The partial isothermal section at 800°C is represented for the first time. The structure of the Al–Cu–Ir alloys in the Al70Ir30–Al40Cu60–Al range, which are quenched from 800°C, is investigated by SEM/EDX and XRD methods. Three ternary phases (decagonal quasicrystalline D1, orthorhombic ε6, and cubic (fcc) C2) are stable at this temperature. The (Al9Ir2), φ, ε6, D1, γ1, and є2 phases coexist with a liquid phase at 800°C.
Keywords: phase diagram; isothermal section; aluminum; iridium; copper; quasicrystal; phase

The β-Mn structure (π-phase) is revealed on contact and free surfaces of Fe63Mo37 melt-spinning ribbons. The full-profile analysis (Rietveld analysis) of diffraction patterns for a mixture of polycrystalline phases has identified, along with the metastable π phase, bcc solid solutions, μ and σ phases, and an intermediate bcc phase in the Fe–Mo phase diagram.
Keywords: manganese-like phases; metastable phase transformations; spinning method; Rietveld analysis

Interaction of Ti–6 wt.% Si alloy with tissue fluid: experimental modeling by V. A. Lavrenko; V. N. Talash; V. V. Lashneva; N. N. Kuz’menko; M. A. Krasovskii (94-98).
The methods of potentiodynamic polarization curves and quantitative Auger electron spectroscopy are used to determine the mechanism whereby a dense protective nanofilm (up to 20 nm thick) forms. The film consists of Ti2O, TiO, and Ti2O3 lower titanium oxides and forms under the layer of TiO2 (10 nm) and oxygen chemisorbed over an orthopedic prosthesis (90.2 at.% Ti–9.8 at.% Si alloy) during electrolysis in a 3% NaCl solution, as the main component of the tissue fluid (Hank’s physiological solution).
Keywords: orthopedic prosthesis; Ti–Si alloy; anodic oxidation; electrolysis of 3% NaCl solution; protective layer of Ti2O, TiO, and Ti2O3 lower titanium oxides

It is established that the cooling rate after hot pressing controls the crystallization and decrystallization in Si3N4–TiO2 (TiH2) composites. The critical cooling rate is 30 deg/min for Si3N4–TiO2 composites and 50 deg/min for Si3N4–TiH2 composites. It is shown that conductivity responds to the microstructural evolution of the composites as defect centers appear. The defects are located at trapping levels of (0.4 ± 0.05)–(1.3 ± 0.05) eV and differ in mutually perpendicular directions. The best combination of properties is shown by the composites with a monotrapping level with an activation energy of 0.8 ± 0.05 eV. These energy levels supposedly belong to the thin layer of amorphous silicon. The nascent defects are probably point defects or an association of point defects because of the low sensitivity of mechanical properties and strong response of conductivity to the cooling rate.
Keywords: silicon nitride; titanium oxide; titanium hydride; hot pressing; cooling rate; microstructure; conductivity

Confinement and aspiration of dust and gas in the production of atomized copper powders by O. D. Neikov; G. I. Vasil’eva; V. G. Tokhtuev (110-115).
A system for the confinement and aspiration of dust and gas emissions is developed. A movable casing installed on an induction crucible furnace prevents air contamination when melt is prepared and atomized to produce copper powders and alloys. The content of harmful admixtures in air at workplaces does not exceed the threshold limit value. The research has provided input data to develop aspiration and dust separation systems for the production of copper powders and alloys.
Keywords: copper; bronze; brass; melt; induction crucible furnace; confinement; atomization; harmful emissions; dust; aspiration; cover; casing

Effect of warm pressing on the mechanical properties and structure of green compacts of heterogeneous copper-based powder by T. A. Epifantseva; V. G. Kayuk; M. B. Shtern; I. D. Martyukhin; A. Yu. Koval; O. V. Mikhailov (116-123).
The paper examines the warm pressing of copper-based powder mixtures with additions of lead, graphite, and tungsten. It is shown that the density increases by 2 to 3% in warm pressing of copperbased powders with additions of lead and graphite at 800 MPa and their bending strength and elastic modulus become almost twice as high. The tungsten content of 20 and 50% of the compact increases the bending strength. Preliminary cold pressing of the samples before warm pressing has practically no effect on material properties and, hence, does not contribute to energy saving.
Keywords: copper; tungsten; lead; graphite powders; pressing pattern; warm pressing; porosity; bending strength; elastic modulus; temperature; pressing force; microstructure