Powder Metallurgy and Metal Ceramics (v.47, #9-10)

Self-propagating high-temperature synthesis of ultrafine and nanosized WC and TiC powders by I. P. Borovinskaya; T. I. Ignat’eva; V. I. Vershinnikov; O. M. Miloserdova; V. N. Semenova (505-511).
The possible application of self-propagating high-temperature synthesis (SHS) for preparing nanosized powders of refractory compounds is examined. The structurization of tungsten carbide and titanium carbide powders produced by SHS with a reduction stage is studied. The synthesis is based on exothermic reactions between tungsten oxide or titanium oxide, carbon, and magnesium metal. The influence of starting-mixture composition, ratio of components, and nature of adjusting additives on the particle size, morphology, and phase composition of WC and TiC powders is analyzed. Procedures are described for recovering tungsten carbide or titanium carbide from intermediate products using chemical dispersion, i.e., chemicothermal treatment of the ground cake in various solutions. As a result, impurities are removed and defect-rich intercrystalline layers are dissolved. Thus the sinter cake breaks into homogenous hexagonal WC or tetragonal TiC particles. The powder is additionally refined when the final product is treated in various solutions: the uniform shrinkage of the particles is observed because of their partial dissolution in acid and alkaline media, while the structure and properties in the central part of the substance or phase remain unchanged. The influence of the dispersion agent on the morphology and particle size of WC and TiC powders is examined. Conditions are determined for producing TiC and WC powders containing up to 80% of particles smaller than 30 nm using SHS with subsequent chemical dispersion. Based on the research, an SHS process is developed for producing ultrafine and nanosized TiC and WC powders on a commercial scale.
Keywords: self-propagating high-temperature synthesis (SHS); refractory compounds; carbides; nanosized powders; chemical dispersion

Plastic flow of porous materials in friction contact area by S. E. Aleksandrov; A. R. Pirumov; O. V. Chesnikova (512-517).
The paper considers the instantaneous stress-strain state in an infinite hollow porous plastic cylinder subjected to simultaneous radial compression and twisting by shear stresses applied to the cylinder surface. It is assumed that the cylinder material obeys a cylindrical yield criterion and associated flow rule. The asymptotic behavior of the equivalent strain rate near the maximum friction surface is studied. It is shown that the distribution of this quantity follows the inverse square root rule near the maximum friction surface. It is noted that the same dependence is observed in the case of incompressible perfect rigid-plastic material. The strain rate intensity factor is found and is compared to that derived from the corresponding perfect rigid-plastic solution.
Keywords: friction; singularity; analytic solution; rigid-plastic material

Pressing and sintering of nanosized hydroxyapatite powders by V. V. Skorokhod; S. M. Solonin; V. A. Dubok; L. L. Kolomiets; V. P. Katashinskii; A. V. Shinkaruk (518-524).
The paper examines the compactability and sintering of nanosized synthetic hydroxyapatite (HA) powders for increasing the durability and strength of HA ceramics. The granulation of HA powders and limitation of the applied pressure prevent delamination in pressing. Porous HA samples show homogeneous nanoporous structure, high compactability, and excellent sinterability, which is better than that of nanosized powders.
Keywords: nanosized hydroxyapatite; nanoporous molding; compactability; sintering

Nanosized WC/MgO powders are synthesized by high-energy ball milling the mixture of WO3, C, and Mg elements in an atomic ratio of 1:1:3 under argon gas atmosphere at room temperature, and the composite is made by plasma-activated sintering. The microstructure of the mixture powders produced by ball milling and the sample consolidated by plasma-activated sintering is investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It is indicated that self-propagating reduction reactions occur between the mixed element powders during high-energy ball milling, leading to the formation of nanosized WC/MgO crystalline particles with an average size of 35 nm after ball milling for 5h. The obtained nanosized WC/MgO powders are consolidated by plasma-activated sintering at 1473K under the pressure in a range of 5 to 7.5 kN for 1.05 ksec, and then WC/MgO composite with nanomicrostructure and full density can be obtained. The WC/MgO composite exhibits high hardness and high fracture toughness in comparison with commercial WC/Co composites.
Keywords: high-energy ball milling; nanocomposite; self-propagating reaction; plasma-activated sintering

Carbon nanotube/copper (CNT/Cu) nanocomposite powders with different volume fractions of multiwall CNTs (MWNTs) are prepared using e electroless Cu deposition method in alkaline citrate bath. The prepared CNT/Cu nanocomposite powders are investigated with HRSEM. The CNT/Cu nanocomposite powders have morphology of implanted CNTs in the copper particles of about 200 nm in size. An electroless deposited pure Cu powder is also prepared by the same method to compare the properties of pure copper samples and the prepared CNT/Cu nanocomposites. The prepared powders undergo XRD and elemental analysis to evaluate the fabricated CNT/Cu nanocomposites. The XRD patterns and elemental analysis inform that the deposited copper is composed of Cu powder and traces of some elements, e.g., sulfur and oxygen. The CNTs/Cu nanocomposite, as well as the pure copper powders, is sintered by spark plasma at 600 °C and compaction pressure of 20 MPa for one min under 10−3 torr vacuum condition. The microstructure of the sintered nanocomposites is investigated with SEM. The CNTs are homogenously distributed in the copper matrix in the case of CNT/Cu nanocomposites with CNT volume fraction up to 10 vol.% has a porosity of 3%, and the porosity increases by increasing CNT volume fraction due to the agglomeration of the CNTs in the copper matrix. The electrical resistivities of the prepared sintered copper and CNT/Cu nanocomposites are measured with four-probe method. The results show that the highest resistivity is 13.5 µΩ · cm for 40 vol.% CNT/Cu.
Keywords: carbon nanotube; electroless copper deposition; sintering; electrical resistivit

Mechanical properties of powder titanium at different production stages. II. Mechanical behavior of porous titanium compacts by E. M. Borisovskaya; V. A. Nazarenko; Yu. N. Podrezov; O. S. Koryak; Ya. I. Evich; A. V. Vdovichenko (538-545).
The mechanical behavior of porous titanium compacts is analyzed. Four-point bending, compression, and Brazilian tests of the samples are conducted. The influence of the porosity and particle size of the initial powder on Young's modulus, ultimate strength, and strain-to-failure of porous titanium is examined. The dependence of the strength and plasticity of compacts on their porosity is analyzed using different tests.
Keywords: porosity; mechanical properties; titanium powder; strain hardening

Mechanochemical synthesis and structure of Ti-Al-B-based alloys by V. E. Oliker; V. L. Sirovatka; T. Ya. Gridasova; I. I. Timofeeva; A. I. Bykov (546-556).
The paper examines how the structure and phase composition of Ti-Al-B alloys evolve at various consolidation stages in the composite powder mechanochemical synthesis and subsequent sintering under pressure. Two powder alloys with different boron content are studied. The amount of aluminum in both initial powder mixtures is the same and corresponds to TiAl. The content of boron is selected so as to form an aluminide matrix with 10 and 25 vol.% borides. It is established that phases form in the mechanochemical synthesis in the following sequence: Ti + Al → Ti (Al) → TiAl3 and Ti3Al → TiAl. Titanium borides are formed simultaneously with TiO2 and TiAl or after them, which confirms that these processes are interrelated. The mechanochemical synthesis for 12 hours in a planetary-ball mill results in the formation of micron particles that have agglomerated or conglomerated (sometimes layered) composite structures. X-ray analysis is used to study the phase evolution of Ti-Al-and Ti-Al-B alloys. It is shown that the presence of boron in mechanical alloying reduces the degree of amorphization and promotes the formation of fine crystalline structure. In addition, the presence of boron prevents the formation of metal oxides and a number of intermetallides. It is established that the sintered dispersion-hardened Ti-Al-B material consists of an aluminide matrix with micron and submicron inclusions of borides. The increase in boron content leads to a higher amount of boride inclusions. As a result, the distance between them decreases and thus microhardness increases.
Keywords: mechanochemical synthesis; mechanical alloying; sintered compacts; titanium aluminide; boride

The paper examines the effect of nickel and phosphorus on the performance characteristics of antifriction graphite-bronze powder materials under high pressures (to 20 MPa), at substantial sliding velocities (1–2 m/sec), and with a liquid lubricant supplied from an oil-impregnated felt pad. It is established that Cu-Ni-P-C graphite bronze of the optimal composition has a friction coefficient of 0.028–0.045 and can perform till 150°C in the above conditions. The material is microheterogeneous: the bearing structural component is α solid solution of nickel in copper with the hardening phase being evenly distributed along its boundaries (Cu3P mesh with inclusions of phosphide eutectic (Cu-Ni) + Cu3P); the antifriction structural component represents graphite inclusions evenly distributed in the material matrix.
Keywords: antifriction graphite-copper material; alloy elements; microheterogeneous structure; bearing and antifriction structural components; pressure; sliding velocity; friction coefficient; temperature

Procedural features of the mesostructural analysis of porous materials are established. It is shown that the experimental pore size is a function of research methods. The anisotropy of the macroporous system in biporous materials is determined. A mercury porometric method is developed for determining the effective porosity needed to evaluate the permeability factor.
Keywords: biporous material; pore size analysis; macroporous structure anisotropy; mercury porosimetry

Experimental data on the erosion of brittle materials in abrasive particle flow are generalized on the basis of similarity and dimension theory using four similarity criteria. These criteria represent the influence of strength, fracture toughness, dynamic and total pressures resulting from the particle-target impact, and target temperature. The volume erosion rate is represented as power dependence of the similarity criteria. It is shown that strength characteristics and total pressure, which results from wave damping in the particle-target impact, are of major importance in the erosion of brittle materials in addition to the impact velocity. Dynamic pressure and temperature are of minor importance.
Keywords: erosion in particle flow; brittle materials; similarity and dimension theory

Al2O3-ZrO2-Yb2O3 phase diagram. IV. Vertical sections by S. M. Lakiza; V. P. Red’ko; L. M. Lopato (577-585).
For more complete presentation of the Al2O3-ZrO2-Yb2O3 phase diagram, three vertical sections are constructed over a wide temperature and composition range. The bisector Al2O3/ZrO2 = 1 discovers the Yb2O3-rich corner of the ternary phase diagram and explains the mechanism of Yb2O3 phase transformation H ⇄ C. The isopleth 15 mole% ZrO2 (15Z) shows the Al2O3-ZrO2-Yb2O3 structure near the Al2O3-Yb2O3 bounding binary system. The bisector Al2O3/Yb2O3 = 1 depicts the ternary system in the ZrO2-rich region. The vertical sections intersect each of the three triangulating sections of the Al2O3-ZrO2-Yb2O3 system and demonstrate the width variation of its two-phase regions.
Keywords: zirconia; alumina; ytterbia; phase diagram; vertical sections

Thermodynamic assessment of the Cu-Ti-Zr system. III. Cu-Ti-Zr system by M. A. Turchanin; T. Ya. Velikanova; P. G. Agraval; A. R. Abdulov; L. A. Dreval’ (586-606).
The thermodynamic assessment of the Cu-Ti-Zr system is carried out in the framework of the CALPHAD method. The Gibbs energy of the liquid alloys is described by the ideal associated solution model. The excess Gibbs energy of the solid solutions is described using the Redlich-Kister-Muggianu model. The Gibbs energy of intermetallic compounds with homogeneity region is described in the framework of the Compound Energy Formalism. A set of self-consistent parameters of models is obtained taking into account data on phase equilibria and thermodynamic properties of the liquid phase. The calculated isothermal and vertical sections of the phase diagram and liquidus and solidus surfaces are in satisfactory agreement with corresponding experimental data. Metastable transformations with participation of the supercooled liquid melts are calculated. Predicted concentration ranges of amorphization are in satisfactory agreement with experimental data.
Keywords: phase diagram; thermodynamics; thermodynamic modeling; copper-titanium-zirconium alloys; amorphous alloys

Corrosion behavior of dispersion-strengthened ferritic Fe-13Cr-2Mo steel in lead melt by O. I. Eliseeva; V. P. Tsisar; I. I. Ivanova; A. M. Demidik (607-615).
The corrosion behavior of dispersion-strengthened ferritic Fe-13Cr-2Mo (TiO2) steel in oxygen-containing lead melt is investigated at 550 and 650°C. It is determined that duplex magnetite scale is formed on the steel surface at 550°C and oxygen concentration of about 10−3 wt.% in the lead melt. The scale grows symmetrically with regard to the initial steel-melt interface toward the liquid metal and matrix. The outer oxide layer consists of Fe3O4, the upper part of which contains plumboferrites, while the inner oxide is Cr-rich spinel Fe1+xCr2−xO4. As the scale grows, the imperfection of the duplex oxide increases. The oxidation intensifies as interaction temperature increases to 650°C. The scale loses its protective properties and becomes penetrable for lead. With decreasing oxygen concentration in the lead melt (10−5 wt.%), the scale growth becomes slower while the corrosion resistance of steel increases.
Keywords: Fe-13Cr-2Mo (TiO2) steel; lead melt; oxidation

Effect of the isotopic composition on the lattice parameter of boron by L. S. Chkhartishvili; D. L. Gabuniya; O. A. Tsagareishvili (616-621).
It is shown that the lattice parameter may be expected to change upon substitution of heavier isotopes by lighter ones in crystalline modifications of boron and their solid solutions and compounds. This isotopic effect is estimated using the diatomic model and semiclassical B-B interatomic interaction potential. The maximum percent change in the lattice parameter after substitution of all 11B atoms by 10B atoms is estimated at 0.42%. This value is of the same order of magnitude as the isotopic changes in the lattice parameter measured in boron carbides.
Keywords: isotopic effect; lattice parameter; crystalline modifications of boron

Structural and phase changes in copper, cobalt, and titanium oxide powders subjected to shock waves by V. I. Kovtun; M. V. Karpets; V. V. Garbuz; S. M. Zakharov; N. V. Zaitseva; O. A. Shmatko; M. V. Bober; A. N. Demidik (622-628).
Powders TiO2, CuO, Cu2O, and CoO mixed with inert filler are subjected to shock waves in cylindrical preservation devices. The shock waves are generated by the explosion of TG40 charge at a detonation speed of 7.8 km/sec and detonation wave pressure of 28 GPa. It is established that shock-wave processing of oxide powders leads to changes in particle-size distribution since coarse and medium particles are crushed, coherent scattering regions become smaller, and concentration of phase distortions increases. Phase transformation of rutile into denser orthorhombic modification occurs in TiO2, and the content of phases with higher oxygen amount increases in Cu2O and CoO.
Keywords: oxides; powders; shock waves