Powder Metallurgy and Metal Ceramics (v.47, #3-4)

Effect of mechanical activation on the formation of Si3N4-SiC composite powders by L. A. Krushinskaya; G. N. Makarenko; V. B. Fedorus; V. E. Matsera; D. P. Zyatkevich; A. V. Yakovlev (157-162).
The paper examines how the mechanical activation of an initial silicon-carbon powder mixture and the temperature of its subsequent treatment influence the specific surface and phase composition of the end products. It is established that the preliminary mechanical activation of Si-C mixtures significantly increases the nitration rate of silicon and decreases the temperatures of formation of silicon carbide and silicon nitride (1200–1300 °C). The products resulting from the nitration of mechanically activated mixtures consist of α-Si3N4 whiskers with an aspect ratio of 10–100, silicon, carbide, and silicon nitride particles to 100 nm in size, and their agglomerates.
Keywords: mechanical activation; particle; composite powder; silicon carbide; silicon nitride

The paper examines how the amount of the liquid phase influences the densification of loose W-Cu and Mo-Cu powder mixtures in liquid-phase sintering at 1200°C, with the content of the low-melting component ranging from 20 to 90 wt.%. It is observed that the density grows continuously with increasing amount of the liquid phase in both W-Cu and Mo-Cu systems. It is shown that samples sintered with a great amount of the liquid phase in the W-Cu and Mo-Cu systems retain their shape.
Keywords: densification; liquid-phase sintering; tungsten; molybdenum; copper

High-porous materials of carbon steel fibers and their mechanical properties by A. G. Kostornov; O. V. Kirichenko; N. P. Brodnikovskii; V. N. Klimenko (171-175).
A base porous material made of pressed and sintered St.10 steel fibers is carburized, hardened, and tempered to produce new porous materials of 60 and U8 hardened steel fibers. Comparing the mechanical properties of porous materials made of St.10, 60, and U8 steel fibers shows the following. In compression tests, the hardened 60 steel material with 70 and 80% porosity has yield stress higher by a factor of 10 and 8, respectively, than that of the base material. In tension tests, the hardened U8 steel material with a porosity of 60–90% has three to six times higher yield stress and tensile strength than those of the base material.
Keywords: porous materials; carbon steel fibers; cementation; hardening; mechanical properties

Ultrafine high-cobalt VK40 hard alloy. I. Structure and properties by A. I. Tolochin; A. V. Laptev; M. E. Golovkova; M. S. Koval’chenko (176-182).
Ultrafine WC-41 wt.% Co powders (VK40) are densified under 1000–1200 MPa at 950–1250 °C and in 0.13 Pa vacuum. It is examined how the pressing temperature and annealing at 1190 °C influence the density, structure, physical and mechanical properties of VK40 alloy. It is shown that high-pressure sintering produces dense samples with ultrafine structure (LWC = 0.35–0.45 µm) and low degree of contact for carbide particles (contiguity CWC = 0.08–0.1) in solid phase. The highest mechanical properties are exhibited by samples densified at 1150–1250 °C or by samples annealed after preliminary pressing at 1050–1150 °C. The alloy has the following properties: transverse rupture strength (TRS) of 3200–3400 MPa, fracture toughness of 25–33 MPa · m1/2, Vickers hardness of 7.5–7.7 GPa under 300 N, compressive strength of 2600–2800 MPa, compressive offset yield stress σ0.2 = 2200–2400 MPa, compressive plastic strain of 6.5–7.0%, and fracture energy of 180–200 MJ/m3. These mechanical properties of ultrafine VK40 alloy differ from those of standard impact-resistant coarse-grained hard metals in higher TRS, fracture toughness, and yield stress.
Keywords: tungsten carbide; cobalt; solid-phase densification; ultrafine structure; mechanical properties

Structure, mechanical and erosive properties of AlN-MoSi2 composite materials and their electrospark-deposited coatings by M. S. Koval’chenko; Yu. G. Tkachenko; V. F. Britun; G. A. Bovkun; D. Z. Yurchenko; A. A. Rogozinskaya (183-190).
The paper examines the phase composition, structure, and properties of AlN-MoSi2 alloys and associated electrospark-deposited coatings on titanium. It is shown that the most intensive erosion and mass transfer are characteristic of alloys containing 60–80 wt.% MoSi2 and that the erosive characteristics essentially depend on the electrospark treatment parameters. A protective coating with a thickness of 30–40 µm and hardness to 1 GPa is formed on the substrate. There is a thermal impact area up to 300 µm deep and 1.4 GPa hard under the coating. The high-temperature holding of coated samples promotes the rapid formation of heat-resistance phases in the coating and the formation of a secondary structure in the thermal impact area. As a result, this area becomes thicker and the hardness of its material increases up to 1.9 GPa.
Keywords: aluminum nitride; molybdenum disilicide; titanium; erosive properties; properties of electrospark-deposited coatings

Diamond-hard alloy macrocomposite material: Development and application by Yu. V. Naidich; A. A. Bugaev; A. A. Adamovskii; V. A. Evdokimov; V. P. Umanskii; N. S. Zyukin (191-196).
A new diamond-hard alloy macrocomposite material consisting of diamond grits (0.5–0.8 mm or more in size) and a WC-Co matrix has been developed. The material is characterized by high mechanical properties of the matrix (the same as for WC-Co monolithic hard alloys) while diamonds remain completely intact (no graphitization or dissolution in cobalt melt). This process does not require superhigh pressures. Hard-alloy samples sintered beforehand in conditions that ensure the maximum mechanical properties (1450–1500°C, 30–60 min holding) are used as initial materials. Hollows (cells) or ditches of specific sizes (depth, width) are made in these samples with mechanical or electrophysical methods, and then diamond crystals (grits) commensurate with the hollows, cells, or ditches are placed in them. Vacuum infiltration (brazing) at moderate temperatures (900–1150°C) with adhesion-active alloys (or metallized diamonds) is the final stage in the formation of the composite. Therefore, strong adhesion-mechanical fixation of diamond grits in the hard-alloy matrix is ensured. The new material is efficiently used in diamond bits.
Keywords: diamond; hard alloy; composite; diamond bits

The paper analyzes the effect of the laser treatment process on the properties of electrospark alloying coatings. The properties are assessed after laser treatment by analyzing the microstructure and measuring the microhardness and friction force. The tests are carried out on a WC-Co coating (the anode) obtained by electrospark alloying over carbon steel St.45 (the cathode) and molten with a laser beam.
Keywords: electrospark alloying; alloy; laser treatment; coating; microstructure; tribology

The Al2O3-ZrO2-Yb2O3 phase diagram. I. Isothermal sections at 1250 and 1650°C by S. M. Lakiza; V. P. Red’ko; L. M. Lopato (202-210).
Isothermal sections at 1250 and 1650 °C of the Al2O3-ZrO2-Yb2O3 phase diagram are plotted for the first time. Phase equilibria are established at these temperatures. No ternary compounds and appreciable solid solution regions based on components or binary compounds are found in the ternary system. A partially pseudobinary section Yb3A5-F triangulating the Al2O3-ZrO2-Yb2O system is established.
Keywords: ceramics; zirconia; alumina; ytterbia; interaction; isothermal section; phase diagram

Phase equilibria in the nickel corner of the Mo-Ni-B system at temperatures close to melting by V. Z. Kubliy; A. A. Bondar; S. V. Utkin; V. M. Petyukh; S. I. Lysenko; T. Ya. Velikanova (211-222).
The Mo-Ni-B alloys prepared by arc-melting are examined in as-cast and annealed states using x-ray diffraction, scanning electron microscopy with electron probe microanalysis, and differential thermal analysis. The temperatures of invariant equilibria are refined. The projections of liquidus and solidus surfaces are plotted for the Ni-rich region.
Keywords: phase diagram; solidus; liquidus; phase; crystal lattice

Thermodynamic assessment of the copper-hafnium system by M. A. Turchanin; P. G. Agraval (223-233).
The thermodynamic properties of phases and phase equilibria in the Cu-Hf system are described with the CALPHAD method. The set of self-consistent model parameters is based on the thermodynamic properties of liquid alloys, intermetallic compounds, and phase equilibria. The excess Gibbs energy of the liquid phase is described using an ideal associated solution model. The models of thermodynamic properties are used to describe possible metastable transformations such as glass formation in rapid quenching from the melt, formation of bulk amorphous alloys, and formation of supersaturated terminal solid solutions.
Keywords: phase diagram; thermodynamic properties; thermodynamic modeling; copper alloys; amorphous alloys

Thermodynamic properties of bismuth sesquiselenide and sesquitelluride and their solid solutions by V. R. Sidorko; L. V. Goncharuk; R. V. Antonenko (234-241).
The Gibbs free energies, enthalpies and entropies of formation of bismuth selenide Bi2Se3 between 308 and 408 K, bismuth telluride Bi2Te3 between 308 and 413 K, and their solid solutions between 670 and 840 K are measured using the e.m.f. method. Positive deviations of the activities of components in the solid solutions from the ideal behavior are found. The possibility of ordering effects in the solid solutions at lower temperatures is assumed.
Keywords: Gibbs free energy; enthalpy; entropy; activity; solid solution; bismuth selenide; bismuth telluride

Interaction of artificial carbon pyroceram mitral valve with blood plasma by V. A. Lavrenko; P. I. Zolkin; V. N. Talash; A. D. Panasyuk; V. V. Los’ (242-247).
The nanocrystalline material of an artificial carbon pyroceram mitral valve obtained by sintering of 15 wt.% B4C with crystals <10 nm that are uniformly distributed in 85 wt.% carbon with particles ∼10 nm has exceptionally high chemical stability in blood plasma. The electrochemical interaction resulting from contact with a possible microadditive (for example, iron) on the valve surface is experimentally modeled by polarization induced by an external current source specially to create extreme corrosion conditions. The interaction kinetics is studied at 37 °C using anodic polarization curves. Curcumin is used as an analytical reagent for spectrophotometry of boron traces in a solution. Emissive spectroscopy is used to determine iron traces in the spume-like film formed after polarization. It is established that a chemisorbed oxygen film forms when microgalvanic elements appear at 0.4 V and stable passivation of the valve surface is observed at ∼1.0 V since a low-conductive nanostructured carbon film forms. It is shown that this film results from the discharge of α-amino acids on the valve surface (amino acid residues of complex peptide chains of plasma proteins) containing heterocyclic rings. The sessile drop method shows that the valve is promptly wetted by blood plasma (wetting angle is 50 °), this also promotes the formation of a stable protective film on its surface.
Keywords: artificial mitral valve; carbon-B4C composite; blood plasma; interaction mechanism; electrochemical polarization; wetting

The types and concentrations of ion polyatomic clusters in glow discharge plasma are calculated in cathode sputtering of Kh13N10T stainless steel in argon. Mass spectra in the mass regions of elements used for microalloying of steels are interpreted. The calculations are performed for high gas background typical of pressured pellets of powder materials. The resolution of mass spectrometer that ensures the necessary detection limit for rare-earth and alkaline-earth elements, B, V, Zr, Nb, and Mo is discussed.
Keywords: glow-discharge mass spectrometry; polyatomic clusters; stainless steel; powders; microalloying; detection limit

High-temperature oxidation-resistant coatings on niobium and its alloys by V. I. Zmii; S. G. Ruden’kii; M. Yu. Bredikhin; V. V. Kunchenko (255-259).
The formation of high-temperature oxidation-resistant coatings on niobium by multicomponent activated diffusion saturation in vacuum is investigated. Thermodynamic calculations of potential chemical reactions that result in anticorrosive protective coatings are performed. Comparative tests of high-temperature oxidation resistance of niobium with protective coatings are conducted at 1700°C in open air.
Keywords: niobium; diffusion; chemical reactions; thermodynamics; high-temperature oxidation resistance

Grinding of Fe-B4C powder charge in an inertial cone mill by G. A. Baglyuk; S. G. Pyatachuk; V. M. Dyadyun; M. E. Golovkova (260-263).
The use of an inertial cone mill to grind iron and boron carbide powder mixtures is examined. The dependence of the particle-size distribution in the mixture after grinding on the maximum particle size is analyzed. It is established that the content of coarse-grained fractions (larger than 100 µ m) substantially decreases as compared with the initial powder even after three grinding cycles. If the number of grinding cycles is increased to 20, the content of finer fractions (smaller than 63 µ m) is only 6 to 8% higher than in powders subjected to 3–12 grinding cycles in the inertial cone mill. Therefore, more than 3 or 6 cycles to produce Fe-B4C powder with the optimal content of the ≤100≤63 µ m fraction are unreasonable.
Keywords: mill; grinding; boron carbide