Powder Metallurgy and Metal Ceramics (v.48, #7-8)

Formation of magnesium titanates by M. M. Ristic; N. Obradovic; S. Filipovic; A. I. Bykov; M. A. Vasil’kovskaya; L. A. Klochkov; I. I. Timofeeva (371-374).
The paper examines the phase formation in the mechanochemical treatment and subsequent annealing of TiO2 and MgO mixtures. It is established that the MgTiO3 phase forms during annealing of the above powder mixtures at 900, 1000, and 1100°C. Preliminary grinding of oxides in a high-energy planetary-ball mill after annealing produces the MgTiO3 phase within its homogeneity range. The lattice parameters are determined at the boundary of the homogeneity region. Preliminary grinding of the oxide mixture produces the spinel-type Mg2TiO4 phase.
Keywords: oxides; grinding; annealing; magnesium titanates

Combustion synthesis of silicon nitride using ultrafine silicon powders by V. V. Zakorzhevskii; I. P. Borovinskaya (375-380).
The paper examines the synthesis of α-Si3N4 using ultrafine powders of silicon and inert diluent (α-Si3N4). It is established that the combustion temperature of the mixture based on silicon particles 200 nm in diameter is lower than the silicon melting point (1420°C). The low combustion temperature is obviously attributed to a nanofraction in the silicon powder. The specific surface area of silicon nitride increases with decreasing silicon fraction in the starting mixture. When Si with S sp = 6 m2/g and 12 m2/g is used, the maximum specific surface area of Si3N4 is 6.5 m2/g and 9.6 m2/g, respectively. The content of the low-temperature Si3N4 (alpha phase) modification remains the same in the synthesis product: α /(α + β) ⋅ 100% = 89–93% (∼95 wt.%).
Keywords: silicon nitride; synthesis; combustion

Thermal synthesis of Fe–B4C powder master alloys by G. A. Baglyuk; S. G. Napara-Volgina; V. I. Vol’fman; A. A. Mamonova; S. G. Pyatachuk (381-383).
The paper examines the thermal synthesis of master alloys from a mixture of iron and boron carbide powders. It is shown that the content of boron decreases as compared with the starting mixture and the boron/carbon ratio in the master alloy powder changes with increasing synthesis temperature. Thus the initial content of boron carbide in the mixture insignificantly influences the boron/carbon ratio after sintering. At the same time, the content of boron carbide in the mixture and synthesis temperature essentially influence the structure and phase composition of the master alloy obtained.
Keywords: master alloys; powder; carbide; iron; carboboride

Asymmetric rolling of metal powders. III. Forward slip in asymmetric rolling of metal powders by K. A. Gogaev; G. Ya. Kalutskii; V. S. Voropaev (384-387).
The paper studies the forward slip that occurs when strips of iron powder and aluminum granules are rolled using drive rolls of different diameters at the same angular velocity. The diameter ratio is from 1.12 to 1.42. It is established that the mismatch between the circumferential velocities of the rolls has a great effect on the forward slip. Forward slip on the large roll is not observed.
Keywords: forward slip; rolling; powder; asymmetry

The formation of internal boundaries in a unidirectional fiber strand during isostatic and uniaxial pressing in plastic state is studied. The process is modeled using the finite-element method (FEM). An ideal contact elastoplastic problem for a hexagonal fiber strand undergoing plane deformation is solved taking into account friction at the boundaries. For angles of 0°, 30°, 60°, and 90° between the normal to the contact area and the pressing direction, the contact area width, change in the contact area slope, and the radius vector of the cross-sectional boundary of the fiber inside the pore channel as functions of density are determined for the friction coefficient at the boundaries of fibers equal to 0 and 0.5.
Keywords: unidirectional fibers; modeling of compaction; finite-element method; contact area width; contact area angle; formation of boundaries; friction; pore channel

The paper considers the hierarchic concept of structural levels in inorganic materials. On the one hand, it reflects the hierarchic structure of matter and, on the other hand, plays a significant part in the well-known materials-science triad: chemical composition–structure–properties. It is the hierarchic concept of structure that may underlie the structural engineering of materials. Special significance of the concept in nanostructured materials science is emphasized.
Keywords: structure; hierarchy; structural engineering; nanostructured materials science

The modern notions of nonequilibrium thermodynamics, synergetics, and thermokinetics of synergy in reacting powder systems underlie the thermochemical kinetics of heterogeneous processes. The kinetic aspect of synergy is associated with local interaction in a gaseous or liquid medium with the maximum degrees of freedom. A liquid or gaseous region in a reacting powder system is regarded as a flow reactor. Applications of the thermochemical kinetics of heterogeneous processes are shown.
Keywords: thermochemical kinetics; local principles; reacting powder systems; synergetics

Uniformly dispersed yttrium aluminum garnet (Y3Al5O12, YAG) ultrafine powders are synthesized by coprecipitating a mixed solution of aluminum and yttrium nitrates with ammonium hydrogen carbonate in the presence of sodium dodecyl sulfate (SDS) as a dispersing agent. The primary purpose of introducing SDS is to protect YAG particles from agglomeration. The evolution of phase composition and microstructure of the as-synthesized YAG powders are characterized by thermogravimetry/differential scanning calorimetry, X-ray diffraction, infrared spectra, and scanning electron microscopy. The results show that phase-pure YAG powders can be achieved by calcination of the precursor at 900°C for 2 h. Uniformly dispersed YAG powders with a particle size of approximately 90–100 nm are obtained with the optimum molar ratio of Al3+ to SDS of 2, and excessive SDS restrains good dispersion of the YAG powders. The dispersion mechanism of SDS in the preparation process is discussed.
Keywords: YAG; powder technology; ceramics; coprecipitation; dispersant

Tribological and corrosive characteristics of electrochemical coatings based on cobalt and iron superalloys by N. Tsyntsaru; A. Dikusar; H. Cesiulis; J.-P. Celis; Zh. Bobanova; S. Sidel’nikova; S. Belevskii; Yu. Yapontseva; O. Bersirova; V. Kublanovskii (419-428).
The tribological and corrosive characteristics of binary and ternary alloys electrodeposited from CoW, FeW, CoMoP, and CoWP citrate solutions are studied. The tungsten content of CoW alloys reaches 31 at.% and of FeW alloys 34 at.%. The introduction of phosphorus into the alloys reduces the content of tungsten from 26.7 to 19.7 at.% (at 4.5 at.% P). The molybdenum content of CoMoP alloys is 0.7–1.0 at.% at 5 to 8 at.% P. The electrolytic tungsten alloys are nanocrystalline and subgrains are 4 to 7 nm in size. The nanohardness of tungsten-rich alloys (∼13 GPa) is comparable with that of electrolytic chromium coatings. The wear resistance of the deposited alloys is quite high and is commensurable with that of hard coatings such as TiB2, TiN, and TiAlN. The tribooxidation of FeW alloys in dry friction is revealed. The corrosion resistance of the coatings is similar to that for electrolytic chromium.
Keywords: tungsten alloys; molybdenum alloys; phosphorus alloys; electrodeposition; wear; corrosion

Properties of spark-deposited Ni–Cr–NiAl coatings by A. V. Paustovskii; R. A. Alfintseva; S. G. Pyatachuk; V. S. Treshchenko; V. I. Novikova; N. M. Mordovets (429-434).
The structure and phase composition of sintered Ni–Cr–NiAl alloys and the kinetics of their electrospark deposition onto 45 steel are examined. It is shown that the mass transfer coefficient for the deposition with the sintered alloys is 50 to 71% lower than that when hot-pressed and cast alloys of the same composition are used. The microhardness and structure of the Ni–Cr–NiAl coatings are studied. It is shown that the structure is characterized by fine conglomerates of the phases––nickel and chromium solid solutions and nickel-aluminum intermetallides.
Keywords: electrospark deposition; mass transfer coefficient; wear resistance; hardness; phase composition; structure

Abrasive wear of ZrB2-containing spark-deposited and combined coatings on titanium alloy. II. Nonfixed-abrasive wear of ZrB2-containing coatings by I. A. Podchernyaeva; A. D. Panasyuk; V. M. Panashenko; O. N. Grigor’ev; A. I. Dukhota; V. V. Zhiginas (435-440).
The kinetics of nonfixed-abrasive wear of spark-deposited and laser-spark coatings on titanium alloy is studied. The coatings are deposited using electrode materials with different ZrB2 contents. It is revealed that the wear rate of the coatings decreases with higher ZrB2 content of the alloying electrode, after laser fusion, which increases the hardness of the outer layer, and with longer deposition of the coating, which increases its thickness It is shown that combined ZrB2-based coating can compete with spark-deposited WC + 3%Co coating.
Keywords: spark-deposited coating; laser fusion; ceramics; abrasive wear kinetics

Wear mechanism of composites based on titanium nitride by T. M. Evtushok; I. A. Kossko; M. V. Karpets; O. N. Grigor’ev; A. D. Kostenko; G. L. Zhunkovskii; T. I. Shaposhnikova; V. A. Kotenko; P. V. Mazur (441-444).
Electron scanning microscopy, Auger spectroscopy, and x-ray diffraction analysis are used to examine the wear mechanism of new antifriction composites based on titanium nitride during friction on steel in air without lubrication. It is established that the TiN lattice parameter decreases in friction regardless of the lubricant composition. This is due to the partial replacement of nitrogen atoms by oxygen atoms and the formation of titanium oxynitride, which substantially increases the wear resistance of materials.
Keywords: composite material; wear mechanism; adhesive interaction; titanium nitride; titanium oxynitride; tribological properties

Interaction of tungsten carbide with aluminum nickelide Ni3Al by V. S. Panov; M. A. Gol’dberg (445-448).
The paper examines the effect of the wetting time on the contact angle θ of WC and Ti wetting by Ni3A melt. It is shown that the equilibrium θ value varies between 38 and 0°. It is established that the miscibility of WC in Ni3Al intermetallic compound is 3 to 4% at T = 1500°C. A differential thermal analysis has revealed that the liquid phase in the WC–Ni3Al system shows up 20 to 25°C lower than the melting point of pure Ni3Al. A microstructural analysis has shown that WC–Ni3Al alloys contain two phases: WC-based phase and solid solution of WC in Ni3Al. The work of adhesion is calculated; it shows that chemical interaction prevails. The microstructure of the contact area is analyzed.
Keywords: carbide; intermetallide; melt; wettability; temperature; solubility; microstructure; contact area; analysis; phase; x-ray pattern

Thermodynamic properties of Lu5Si3 over a wide temperature range by N. P. Gorbachuk; V. R. Sidorko; S. N. Kirienko; I. M. Obushenko (449-453).
The heat capacity and enthalpy of Lu5Si3 between 53 and 2403 K are examined for the first time. The values of heat capacity, entropy, Gibbs reduced energy (J ∙ mole–1 ⋅ K–1), and enthalpy (J ⋅ mole–1) are determined at 298.15 K: Cp°(T) = 189.82 ± 0.76; S°(T) = 277.1 ± 2.3; Φ′(T) = 143.0 ± 2.2; H°(T)–H°(0 K) = 39984 ± 200. Temperature dependences of Lu5Si3 enthalpy (J ⋅ mole–1) are determined as: H°(T) – H°(298.15 K) = 27.555 ⋅ 10–5 ⋅ T–2 + 190.34 ⋅ T + 1507230 ⋅ T–1 – 64256; H°(T)–H°(298.15 K) = 449.58 ⋅ T – 134042 for 298.15–2330 K and 2330–2403 K, respectively. The temperature, enthalpy, and entropy of Lu5Si3 melting are calculated: Tm = 2330 ± 40 K, ∆Hm = = 384.0 ± 23.1 kJ ⋅ mole–1, ∆Sm = 164.8 ± 9.9 J ⋅ mole–1 ⋅ K–1.
Keywords: thermodynamics; heat capacity; enthalpy; entropy; Gibbs reduced energy; silicide

Mixing enthalpies in samarium–transition metal melts by V. V. Berezutskii; M. I. Ivanov (454-461).
The mixing enthalpies in homogeneous melts of samarium with transition metals (Cr, Mn, Fe, Co, Ni) are measured by high-temperature calorimetry over the entire concentration range (in the Sm−Cr system up to 10 at.% Cr). The mixing enthalpies gradually change from positive (Sm−Cr system) to sign-variable (Sm−Mn system) and finally to negative (Sm−Fe, Sm−Co, and Sm−Ni systems). The extreme values of the integral enthalpy are (kJ/mole): 0.96 ± 0.17 and −0.69 ± 0.19 (Sm–Mn, 1600 K); −4.20 ± 0.93 (Sm–Fe, 1829 K); −14.63 ± 1.91 (Sm–Co, 1829 K); and −34.62 ± ± 1.73 (Sm−Ni, 1780 K).
Keywords: samarium; chromium; manganese; iron; cobalt; nickel; melt; enthalpy; calorimetry

Kinetics and mechanism of the electrochemical oxidation of hafnium boride by V. A. Lavrenko; V. N. Talash; M. Desmaison-Brut; O. N. Grigor’ev; Yu. B. Rudenko (462-465).
The kinetics and mechanism of the anodic oxidation of HfB2 samples in a 3% NaCl solution (composition of marine water), which are produced by high-temperature isostatic pressing, are studied using potentiodynamic polarization curves, x-ray diffraction, Auger electron spectroscopy, electronography, and scanning electron microscopy. It is established that an oxide film consisting of three nanolayers results from electrolysis on the HfB2 surface. Its upper layer (5 nm thick) contains B2O3 boron oxide with inclusions of Hf(BO2)4 and B6O crystallites under chemisorbed oxygen, while the middle layer (20 nm thick) consists of nonstoichiometric HfO0.5, B6O, and B12O lower boron oxides. The third layer (15 nm thick) adjacent to the sample is 5% O2 solid solution in HfB2.
Keywords: hafnium boride; electrochemical oxidation; HfO0.5 ; Hf(BO2)4 ; B2O3 ; B6O; B12O oxidation products

Effect of magnetic abrasive treatment on high-temperature oxidation of NiAl and NiAl–Re coatings by V. E. Oliker; T. Ya. Gridasova; V. L. Sirovatka; E. N. Eliseeva; I. I. Timofeeva; E. F. Grechishkin (466-477).
A comparative microstructural analysis of the scale formed on the NiAl–Re detonation coating shows that the mechanism of its high-temperature oxidation can be changed with preliminary magnetic abrasive treatment (MAT). The scale formed over the NiAl–Re coating in ordinary conditions includes several layers (NiO–NiAl2O4–Al2O3), while the scale formed on the MAT coating consists of an Al2O3 monolayer with spinel inclusions. The differences in the oxidation of the NiAl and NiAl–Re coatings after MAT are attributed to changes in their dislocation structure.
Keywords: NiAl; rhenium; eutectic alloy; detonation coating; oxidation; magnetic abrasive treatment

Evolution of phase composition in the thermal decomposition of nanosized aluminum hydroxides by S. V. Gabelkov; R. V. Tarasov; N. S. Poltavtsev; Yu. P. Kurilo (478-484).
The thermal decomposition of nanosized aluminum hydroxides, which are precipitated from solution in direct and inverse mixing of the chemical agents, is studied. The thermal treatment of hydroxides between 370 and 870 K results in their two-stage thermal decomposition. Intermediate decomposition products are amorphous aluminum oxyhydroxide AlO(OH)1+x and boehmite. Nanosized γ-Al2O3 begins forming even at 570 K. The thermal decomposition of amorphous oxyhydroxide AlO(OH)1+x ceases when amorphous alumina forms at 770–870 K. This results in powders representing a mixture of amorphous and γ-alumina.
Keywords: nanosized; aluminum hydroxide; aluminum oxyhydroxide; amorphous alumina; γ-alumina; evolution; precipitation from solution; thermal decomposition; phase composition

Temperature controller of dilatometer furnace by V. I. Vasilenko (485-487).
To examine the sintering of powders immediately in a dilatometer furnace, the temperature of a sample needs to be in a linear relationship with heating time. We developed a temperature controller that reduces the deviation of this relationship from a straight line by 95%, which is due to a special feedback signal obtained by averaging the signals from the sample and furnace thermocouples.
Keywords: powder sintering; temperature controller; dilatometer; furnace heater; sample; heating rate