Powder Metallurgy and Metal Ceramics (v.53, #7-8)

Synthesis of Binary Titanium Compounds TI3ALC2 and TI4ALN3 by Isothermal Sintering by I. I. Ivanova; A. N. Demidik; M. V. Karpets; N. A. Krylova; A. P. Polushko; S. A. Firstov (377-385).
The synthesis of Ti3AlC2 and Ti4AlN3 by isothermal sintering in vacuum is studied. The influence of the original powders, charge composition, and conditions of milling and sintering temperature on the phase composition of the material is analyzed. It is established that single-phase compounds form if and when the aluminum content in the original charge is higher than its stoichiometric amount by a factor of 1.4–1.6 for Ti3AlC2 and by a factor of 1.1–1.2 for Ti4AlN3. Conditions for producing single-phase Ti3AlC2 and Ti4AlN3 with the required TiC or TiN content were determined. The mechanical properties of the obtained materials in the 20–1300°C range were investigated. Results were compared with the mechanical properties of the previously obtained Ti3SiC2.
Keywords: sintering; complex carbides; mechanical characteristics; aluminum; titanium

Metallothermic Reduction and Direct Synthesis Techniques in Production of Chromium Disilicide by L. A. Molotovska; D. B. Shakhnin; V. V. Malyshev (386-391).
Chromium disilicide was obtained by metallothermic reduction of chromium- and silicon-containing compounds with active metals and direct synthesis of disilicide from elemental chromium and silicon in Sn–Zn melt. The metallothermic reduction of chromium and silicon compounds with metallic sodium resulted in CrSi2 in the form of a nanocrystalline powder with an average particle size of 20–60 nm. The direct synthesis in a metallic melt resulted in disilicide in the form of dendrites 150–200 μm long. X-ray diffraction indicates that all CrSi2 products have hexagonal structure. Thermogravimetric analysis and differential scanning calorimetry show that the surface oxidation of samples began at 873–973 K in air. Only a minor part of the sample surface was oxidized, which is indicative of its high corrosion resistance.
Keywords: chromium disilicide; nanocrystalline powder; metallothermic reduction; direct synthesis; corrosion resistance

Synthesis of Ti3SiC2 Through Pressureless Sintering by Maoquan Xue; Hua Tang; Changsheng Li (392-398).
Ternary compound Ti3SiC2 was synthesized by pressureless sintering the powder mixture of 3Ti/1.2Si/2C, 3Ti/1.2Si/2C/0.1Sn, and 3Ti/1.2Si/2C/0.1Al with preliminary liquid magnetic stirring. The Ti3SiC2 was synthesized at 1400°C for 30 min. The addition of appropriate Al amount enhanced the synthesis of Ti3SiC2. The mechanism of Ti3SiC2 synthesis from 3Ti/1.2Si/2C/0.1Al was presumed to be the reactions between the intermediate phases of Ti–Al and Ti–Si intermetallics and other reactants in the starting powder. The Ti–Al and Ti–Si liquid interaction occurring at high temperatures was found to assist the synthesis reaction of Ti3SiC2.
Keywords: Ti3SiC2 ; pressureless sintering; synthesis mechanism; liquid reaction; high temperature

In this study, nanocoatings and/or nanopowders CdO, Cd3N2, Cu, Cu2O, α-C3N4, α-Si3N4, and β-Si3N4 were produced using an organic solvent (acetonitrile) by activation in an electrochemical cell at a high voltage gradient (400–2000 V/cm) and different modes of non-equilibrium process on the electrodes (cathodes and anodes) in the systems Cd–Ni, Cu–Cu, and Si–Si. To explain the nature of the cathode and anodic reactions with HCOOH formic acid as an electrolyte, the Christiansen–Kramers concept for the Semenov–Hinshelwood classical kinetic theory was used along with results of previous investigations for the appropriate transformation of organics and radicals (using massspectrometry and secondary ion-ion emission). It was established that, in some cases, secondary reactions (parallel to electrolysis reactions) could take place on the corresponding electrodes according to the mechanism of heterogeneous catalysis.
Keywords: high voltage gradient; acetonitrile; electrolysis; activation of non-equilibrium processes at electrode–electrolyte interface; producing nanocoatings and nanopowders of metals; oxides; and nitrides

The Structure and Properties of Powder Copper Hardened by Fine Tungsten Particles by P. Ya. Radchenko; O. I. Get’man; V. V. Panichkina; V. V. Skorokhod; Yu. N. Podrezov; D. G. Verbilo; A. V. Laptev; A. I. Tolochin (404-410).
The Cu–W pseudoalloys with 2–10 vol.% of nanosized tungsten particles (30–40 nm) are studied. The bulk samples with relative density up to 99.1–99.6% are produced by shock compaction. The introduction of nanosized tungsten particles increases the pseudoalloy strength to 2.7HCu with insignificant reduction in plasticity (δ = 13%) and conductivity (to δ = 0.875% IACS for the pseudoalloy with 10 vol.% W). The microstructures of the Cu–W pseudoalloys are analyzed.
Keywords: pseudoalloy; copper; tungsten; precipitation hardening; conductivity

Tribological Characteristics of the Iron-Based Composite at 500°C by A. G. Kostornov; O. I. Fushchich; T. M. Chevychelova; A. D. Kostenko; M. V. Karpets (411-416).
The tribological characteristics of the Fe–W–CaF2 composite antifriction material (CAM) in combination with 1Kh18N9T steel are examined in air at a temperature of 500°C, a pressure of 0.8 to 3.3 MPa, and a sliding velocity of 0.5–2.0 m/sec. It is established that the friction coefficient, mass wear Im, and linear wear Il of the composite decrease, respectively, from 0.3 to 0.26, from 5 to 2 mg/km, and from 30 to <5 μm/km at constant pressure (0.8 MPa) with increase in the sliding velocity from 0.5 to 2 m/sec. At a constant sliding velocity (0.5 m/sec), with increase in pressure on the tribological system from 0.8 to 3.3 MPa, the friction coefficient f decreases from 0.3 to 0.26, whereas its mass wear Im and linear wear Il increase from 5 to 8.4 mg/km and from 30 to 57 μm/km. It is shown that secondary lubricating films form in friction on the working surface of the material. Like the starting material, they have a microheterogeneous structure and determine antifriction properties. The bcc solid solution of tungsten in α-iron hardened by inclusions of iron tungstate is a bearing structural component of the secondary lubricating films, and inclusions of iron oxides and calcium fluoride are antifriction structural components. The presence and content of the phases as well as the percentage of structural (antifriction and bearing) components in the secondary lubricating films depend on friction conditions (P · V). With increasing amount of the bearing structural component in the secondary film, wear of the material decreases. Higher content of the antifriction structural component in the film decreases the friction coefficient of the material.
Keywords: composite; microheterogeneous structure; bearing and antifriction structural components; phase composition; temperature; pressure; sliding velocity; friction coefficient; linear and mass wear; secondary lubricating film

Metallographic and X-ray diffraction analyses are used to examine the structure of boride coatings produced by saturation of iron and iron–carbon blanks with different porosities at 1000 and 1100°C and microhardness distribution along their depth is analyzed. It is shown that the thickness of the oxide layer increases with the original porosity of the blanks, but its density and surface microstructure is higher for samples with lower porosity produced at higher saturating temperatures. The morphology of boride layers depends on the porosity of the blanks.
Keywords: boriding; boride; porosity; microhardness; phase composition

The Structure and Properties of Calcium Phosphate Ceramics Produced from Monetite and Biogenic Hydroxyapatite by E. E. Sych; N. D. Pinchuk; A. B. Tovstonog; M. E. Golovkova; A. V. Kotlyarchuk; Ya. I. Evich; V. V. Skorokhod; I. I. Savkova (423-430).
It is shown that porous calcium phosphate ceramics can be produced from monetite and biogenic hydroxyapatite, the starting materials being in the ratios 25 : 75, 50 : 50, and 75 : 25 wt.%. It is established that phase transitions and solid-phase reactions take place during sintering to form polyphosphate ceramics consisting of hydroxyapatite (Ca5(PO4)3(OH)), β-pyrophosphate (β-Ca2P2O7), and β-tricalcium phosphate (β-Ca3(PO4)2), in which β-Ca2P2O7 and Ca5(PO4)3(OH) phases are predominant, depending on starting composition. When the biogenic hydroxyapatite content changes from 25 to 75 wt.%, the grain size decreases and the pore size increases. The ceramics have 40 to 42% porosity with predominant open porosity for all compositions. The ceramics show 32–55 MPa strength, which increases with the amount of biogenic hydroxyapatite in starting composition.
Keywords: biogenic hydroxyapatite; monetite; calcium pyrophosphate; tricalcium phosphate; bioceramics; structure

The paper shows that X-ray diffraction can be used to evaluate changes in the energy content of materials after mechanical activation to determine the energy characteristics of powder tungsten and molybdenum carbides in the feedstock preparation process. This is important for controlling the properties of tungsten carbide hardmetals and inoculating castings using molybdenum carbides.
Keywords: tungsten and molybdenum carbides; mechanical activation; metal organics; X-ray diffraction; energy content

Complex Doped Zirconia for Ceramic Implants: Production and Properties by A. V. Shevchenko; V. V. Lashneva; E. V. Dudnik; A. K. Ruban; V. P. Red’ko; D. G. Verbilo; L. I. Podzorova (441-448).
The physicochemical properties of ZrO2-based composite in the ZrO2–Y2O3–CeO2–CoO system, which is intended for the development of bioinert implants, are examined. To produce the starting nanocrystalline powder, hydrothermal synthesis in alkaline medium and mechanochemical treatment were successively used. The samples were consolidated by cold uniaxial pressing, sintering in air, and barothermal treatment in argon. This resulted in the fine-grained composite consisting of (mol.%): 96.3 ZrO2–2.8 Y2O3–0.6 CeO2–0.3 CoO. The composite has properties that comply with international standards and is not prone to ageing.
Keywords: zirconia; ZrO2–Y2O3–CeO2–CoO system; composite; implant; nanocrystalline powder; physicochemical properties; low-temperature phase stability

The Structure and Properties of Si6–z Al z O z N8–z Sialons Hot-Pressed from Powders with Activating Oxide Additions by I. P. Neshpor; A. D. Panasyuk; O. V. Pshenichnaya; V. A. Lavrenko (449-457).
The densification and phase formation during hot pressing of three compositions of β′-sialon powders produced from natural raw materials (kaolin) by carbothermal reduction in nitrogen atmosphere are studied. It is determined that the onset temperature of shrinkage decreases with increase in z index. The influence of Y2O3, La2O3, and Sc2O3 additions that activate sintering is examined. Eutectic Sc2O3–A12O3, La2O3–Al2O3, and Y2O3–A12O3 additions activate densification at the initial stage of sintering. It is established that the sialon material with Y2O3–A12O3 addition has the best properties; its strength, fracture toughness, and hardness are close to those of the materials produced by reaction hot pressing from Si3N4, A1N, A12O3, and Y2O3 preliminary synthesized components.
Keywords: kaolin; natural raw material; pressing of β′-sialon powders; influence of rare-earth metal oxide additions; hardness; fracture toughness; strength; high-temperature oxidation resistance

Thermodynamic Properties of Holmium Germanides by V. R. Sidorko; L. V. Goncharuk (458-468).
The Gibbs free energy, enthalpy, and entropy of forming holmium germanides HoGe3–x (HoGe2,7), HoGe2–y (HoGe1,8), HoGe2–a (HoGe1,7), HoGe2–b (HoGe1,5), Ho3Ge4, HoGe, Ho11Ge10, Ho5Ge4, and Ho5Ge3 are determined by measuring electromotive forces in the temperature range 770–970 K. The negative values of the Gibbs free energy and enthalpy of formation increase with holmium content in a compound and reach extreme values for Ho5Ge3, which has the highest melting point and is the only congruently melting compound in the Ho–Ge system. The thermodynamic properties of forming solid and liquid alloys of holmium with germanium are compared. Like the solid alloys, the highest enthalpy of mixing is in the range of Ho-rich compositions. The standard enthalpy and entropy of formation of HoGe1.5, HoGe, and Ho5Ge3 are calculated.
Keywords: Gibbs free energy; enthalpy and entropy of formation; holmium germanides

Experimental data are used for the first time to refine the prediction of elements in the Al2O3–HfO2–Ln2O3 phase diagrams and confirm the prognosis for three-phase eutectics in the Al2O3-rich regions. It is established that a series of eutectics solidify through cooperative solidification of the phases. The highest melting temperature in the system is 2820°C, corresponding to the HfO2 melting point. The minimum melting temperatures in the systems range from 1600 to 1760°C and correspond to the melting points of Al2O3-rich three-phase eutectics. Materials in these systems are promising for the development of high-temperature structural composites based on directly solidified two-phase and three-phase eutectics, materials for thermal barrier coatings, materials for solid electrolytes (SOFCs, oxygen sensors, etc.), and refractories.
Keywords: ceramic oxides; hafnium dioxide; lanthanide oxides; interaction; phase diagram; phase equilibria; eutectic materials

Structure of the Eutectic in the LaB6–ScB2 System by G. P. Kysla; P. I. Loboda; L. Geshmati (479-484).
Alloys in the LaB6–ScB2 system are synthesized using unis for electron-beam melting and induction zone melting without crucible in pure helium. Metallographic analysis and X-ray diffraction are used to establish that the alloys form an eutectic with 50 wt.%, 56 vol.%, and 78 mol.% ScB2, whose colonies solidify as cubic bicrystalline lanthanum hexaboride and plates of scandium diboride. In the solidification process, the plates divide into rods under the influence of scandium dodecaboride ScB12, resulting from scandium diboride evaporation.
Keywords: eutectic; directional solidification; lanthanum hexaboride; scandium diboride

Structurization of Materials in the Si–C System Under Shock Compression by A. V. Kurdyumov; V. F. Britun; A. I. Danilenko; V. V. Yarosh (485-489).
Experiments on shock compression of Si + C powder mixtures were performed in annular recovery capsules at pressures of 20 and 30 GPa. The phase composition and structure of the compressed products were examined by X-ray diffraction and transmission electron microscopy. The results demonstrate the importance of silicon melting in the structurization of SiC + Si mixtures that occurs at high shock pressures.
Keywords: silicon; carbon; silicon carbide; shock compression; structure

Studying the Oxidation of Commercial Boron Carbide Powders by Chemical Analysis Methods by V. V. Garbuz; M. D. Bega; V. A. Petrova; L. S. Suvorova; L. M. Kuz’menko; S. K. Shatskikh (490-496).
Acceptance testing of the elemental and phase composition of two commercial examples of boron carbide has been conducted. Complex oxidation reactions for carbon components in situ and boron at 973–1473 K are studied. Thermal, dynamic, and energy activation characteristics of these processes are provided.
Keywords: boron carbide; oxidation reaction