Powder Metallurgy and Metal Ceramics (v.54, #9-10)

Low-Temperature Synthesis and Characterization of Spinel Ferrite Powders by V. S. Bushkova; B. K. Ostafiychuk (509-516).
Nanoparticles of NiAlxFe 2–x O 4 (x = 0; 0.1; 0.2; 0.3; 0.4, and 0.5) are synthesized by sol–gel method with auto-combustion. X-ray diffraction patterns confirm the single phase spinel structure of the samples produced. The scanning electron microscope images indicate that the particle size of the samples lies in a nanometer range. Synthesized in this manner, the powder has high crystallinity and good morphological homogeneity. It is observed that the grain size decreases from 46 to 18 nm as the nonmagnetic Al content increases. The lattice constant and radiodensity of ferrites depending on the content of the component x are determined. The structural and adsorption characteristics of the synthesized samples are determined by analyzing nitrogen sorption isotherms at 77 K. It is demonstrated that the samples produced are mesoporous because their pores are 2–5 nm in size. The thermal processes are investigated by thermal analysis and infrared spectroscopy. It is established that the nitrate-citrate gel burns automatically and then directly transforms into nanosized ferrite particles.
Keywords: sol–gel process ; Ni–Al ferrite ; nanoparticles ; thermal analysis ; infrared spectroscopy

Vortices in Noncompact Blanks During Twist Extrusion by D. V. Pavlenko; Ya. E. Beygel’zimer (517-524).
The causes and consequences of the formation of multifractal vortices during severe plastic deformation of powder and porous bodies by twist extrusion are analyzed. It is demonstrated that the developed pore space in noncompact blanks leads to the formation of self-similar vortices at different scales. It is established that the multifractal vortices occurring during simple shear in twist extrusion, are responsible for the differences in the mechanisms of hardening of compact and noncompact materials. Being significantly increased (in comparison with the concentric streamlines during deformation of compacted materials), the integral deformation path intensifies the accommodation of particles of a mixture of powder components. In addition, the vortices cause intensive mixing and mass transfer at both micro and macro scales. The intensive mass transfer leads to chemical and structural homogenization and elimination of porosity.
Keywords: twist extrusion; fractal; vortex; noncompact material; compaction; homogenization; mass transfer; powder

A powder body model has been developed to study mass transfer through movement of the material as sliding blocks (packs) simulating particles and grains in polycrystals. The key model parameters are grain size and mobility of intergranular boundary layers. The theoretical analysis has resulted in mathematical relations showing that transfer of the material to fill the pores intensifies with transition to finer grains (subgrains, particles) and with higher mobility of the material in boundary layers between the grains. The boundaries between grains and particles experience greater heating during electric current sintering. Temperature in the boundary zone remains higher than the area far from the boundaries, consequently leading to greater mobility of the material. This improves intergranular slip and promotes fast and ultrafast shrinkage.
Keywords: sliding grains (blocks; packs); mobility of intergranular layers; increased electric heating of intergranular layers

Aluminum has long been used as conductor in high-voltage electric transmission due to its economic value and high conductivity. By adding nanosized ceramic particles such as Al2O3 and also alloying elements such as zirconium (Zr), cerium (Ce), and magnesium (Mg), the aluminum performance in strength could be improved without compromising much of its electrical conductivity. The purpose of this research is to investigate the mechanical, electrical, and physical properties of Al–0.12% Zr–0.015% Ce reinforced with different volume fraction (from 0.5 to 1.5%) Al2O3 nanoparticles with addition of 3 and 5 wt.% Mg produced by stir casting route. A master alloy, which consists of aluminum alloyed with Zr and Ce, was produced. The master alloy was then melted and Mg along with the reinforcement was blended inside the molten metal by stirrer with rotational speed of 500 rpm at 850°C in an inert gas environment. The molten composites were casted into plate and tensile test sample molds. The tensile strength of the nano composite was optimal at 1.0 and 1.2 vol.% Al2O3np with addition of 3 and 5 wt.% Mg, respectively. Higher Mg content produced nanocomposites with better strength and elongation. It was found that the conductivity of the nanocomposites is generally decreased with addition of reinforcement because of isolator particles and increasing of Mg content leads to further decrease in conductivity. It was found that the coefficient of thermal expansion could be decreased by adding more Al2O3np. However, adding more Mg generally increases the nanocomposite CTE value. The microstructure observations showed that the composites yield finer grains and more pores, than the unreinforced alloy.
Keywords: stir casting; conductivity; nanocomposite; tensile test; tensile strength; master alloy; addition; strength; elongation

Features of Structurization During Sintering of Compacts from a Multicomponent Ti–Cr–Fe–Ni–Cu Charge by G. A. Baglyuk; M. V. Marich; A. A. Mamonova; A. N. Gripachevskii (543-547).
A heterophase alloy with hardness 103 HRB and a porosity of ~5% is produced by sintering compacts from a Ti–Cr–Fe–Ni–Cu multicomponent charge. It is demonstrated that after sintering a mixture of elemental powders, four phases with different types of lattice are formed: (i) two multicomponent phases with FCC-lattice, (ii) one Cr–Fe phase with BCC-lattice, and (iii) one phase with HCP-lattice with crystallographic constants based on titanium lattice. Well-defined peaks of Cr2Ti, Fe2Ti, and Ni3Ti intermetallides are seen in the X-ray photograph of the alloy.
Keywords: powder metallurgy; multicomponent alloy; sintering; solid solution; crystal lattice

Synthesis and Study of High-Purity Nanocrystalline Powder of a Solid Solution of CeO2 and Y2O3 in Zirconium Dioxide by A. V. Shevchenko; V. V. Lashneva; A. K. Ruban; V. V. Tsukrenko; E. V. Dudnik (548-553).
A technology for synthesizing a high-purity nanocrystalline powder of zirconia doped with yttrium oxide and ceric oxide, namely ZrO2 (5% Y2O3 and 3% CeO2), is developed. The powder is characterized by high activity during sintering and the absence of hard agglomerates. The technology can be used to synthesize powders for manufacturing structural, functional, and medical purpose non-ageing ceramics.
Keywords: nanocrystalline powder; zirconia; yttrium oxide; ceric oxide; hydrothermal synthesis; chemical purity

Structure and Properties of Ni3Al Intermetallic Under Vacuum Impact Sintering by A. V. Laptev; A. I. Tolochin; M. S. Kovalchenko; Ya. I. Evich; I. Yu. Okun’ (554-567).
The compaction, structure, and mechanical properties of Ni3Al intermetallic, corresponding to PN85Yu15 commercial powder and mainly consisting of 50–100 μm particles, are studied. The preforms were subjected to impact sintering in 0.013 Pa vacuum at 1100, 1150, 1200, 1250, and 1300°C. Isothermal holding at these temperatures lasted for 20 min. The samples were compacted at an impact energy of 1200 J/cm3 and an initial impact velocity of 6.5 m/sec. The disk samples were used to cut out rectangular bars to determine their density, resistivity, bending, tensile, and compression strength, conditional fracture toughness, and fracture energy (for notched samples). The Vickers hardness and plasticity of the samples were evaluated in different types of tests. The mechanical properties of Ni3Al intermetallic powder samples compacted at 1250°C and higher temperatures are consistent with those of the standard conventionally melted intermetallic. In particular, the average bending strength is 650–675 MPa, tensile strength 385–400 MPa, fracture toughness 14.6–18.2 MPa · m1/2, compression strength 1650 MPa, and Vickers hardness 2500–2600 MPa.
Keywords: Ni3Al intermetallic; impact sintering; structure; properties; hardness; fracture toughness

Alloy Constitution and Phase Equilibria in the Hf-Ru-Rh System. I. Solidus Surface of the Partial Hf–HfRu–HfRh System by L. S. Kryklya; K. E. Kornienko; V. G. Khoruzhaya; V. M. Petyukh; L. A. Duma; V. B. Sobolev (568-582).
The data obtained by physicochemical analysis techniques are used for the first time to determine the nature of phase equilibria in the Hf–Ru–Rh system at 50−100 at.% Hf (Hf–HfRu–HfRh partial system) at subsolidus temperatures and to construct the solidus surface on the composition triangle. It is established that there is a continuous series of solid solutions between isostructural (CsCl type) HfRu-based and high-temperature δ-HfRh phases. This allowed triangulation of the Hf–Ru–Rh system into two partial ones at 50 at.% Hf. The β-Hf solid solution, γ-Hf2Rh phase (Ti2Ni structure), and δ-phase, forming three single-phase regions on the solidus surface, participate in the phase equilibria at subsolidus temperatures. The ruled surfaces formed by the δ<β-Hf> and δγ tie lines decrease from the bounding binary systems to theδ <β-Hf>γ isothermal plane at 1373°C and the γ<β-Hf> ruled surface decreases in turn to the Hf–Rh binary system.
Keywords: solidus surface ; phase ; compound ; ruled surface ; isothermal plane

The Constitution of Co–Zr Phase Diagram by O. L. Semenova; V. M. Petyukh; O. S. Fomichev (583-589).
The constitution of Co–Zr alloys in the Zr2Co–Zr region is studied by physicochemical analyses (metallography, X-ray diffraction, differential thermal analysis). It is shown that the Zr3Co phase exists in the system, though the literature data on its existence and formation are contradictory. It forms in solid state at 981°C via peritectoid reaction <β-Zr> + 2Co> ↔ 3Co>, and its homogeneity range at 900°C is no larger than 1 at.%. The eutectic point L ↔ <β-Zr> + 2Co> is found in the alloy with ~22 at.% Co. The microhardness of the Zr2Co and Zr3Co phases is determined.
Keywords: cobalt; zirconium; phase; phase equilibria

Thermodynamic Properties of Ce–Ni Binary Alloys by M. I. Ivanov; V. V. Berezutskii; M. O. Shevchenko; P. M. Subotenko; V. G. Kudin; V. S. Sudavtsova (590-598).
The mixing enthalpies of liquid Ce–Ni binary alloys (0 < xNi < 0.45 at 1430 K and 0.78 < xNi < 1 at 1820 K) are determined by isoperibol calorimetry. The thermodynamic properties of the liquid Ce–Ni binary alloys are calculated for the entire composition range using the model of ideal associated solutions. The thermodynamic activities of components show negative deviations from the ideal behavior. The mixing enthalpies are characterized by significant exothermic effects. The minimum mixing enthalpy of the melts is –34.8 ± 0.9 kJ/mol at xNi = 0.66 and 1820 K.
Keywords: cerium ; nickel ; thermodynamics ; enthalpies ; melts

The high-temperature oxidation of AlN–TiCrB 2 composites in air up to 1600°C is studied in the composition range from 5 to 50 wt.% TiCrB 2 . The structure and phase composition of oxide layers formed in the temperature range 1200–1600°C are determined by thermal gravimetry, metallography, electron microprobe analysis, and scanning electron microscopy. It is established that Ti–Cr–O lower solid solutions (Cr 2 Ti 7 O 7 and Cr 2 Ti 4 O 11 ), α-Al 2 O 3 , and TiO 2 (rutile) form in the temperature range 1200–1350°C during oxidation of the samples. When temperature increases to 1500–1550°C, the oxidation products contain Cr 2 TiO 5 , β-Al 2 TiO 5 , and (AlCr 2 )TiO 3 . They form a homological series of isomorphic solid solutions, representing a fine self-reinforced oxide film, which leads to exceptionally high oxidation resistance (>1600°C) of the AlN–TiCrB 2 ceramic composites.
Keywords: AlN–TiCrB 2 ceramics ; high-temperature oxidation ; fine self-reinforced oxide film

Effect of Electron Density on Phase Composition of High-Entropy Equiatomic Alloys by S. A. Firstov; V. F. Gorban’; N. A. Krapivka; M. V. Karpets; É. P. Pechkovskii (607-613).
A series of high-entropy equiatomic alloys have been analyzed to determine the main factors that influence the formation of various solid solutions and chemical compounds. The key factor leading to the formation of phases in high-entropy equiatomic alloys is mean electron density (e/a). The necessary condition for the high-entropy σ-phase to emerge is the presence of elements forming it in two-component alloys in various ratios, the electron density of the alloy is to be between 6.7 and 7.3 e/a. The Laves phase shows up in the high-entropy equiatomic alloys at a mean electron density of 6–7 e/a in the presence of atoms differing by more than 12% in size and having mixing enthalpy lower than −30 kJ/mol. It is revealed that the lattice parameter in bcc high-entropy equiatomic alloys influences their elastic modulus and hardness.
Keywords: high-entropy alloys ; electron density ; elastic modulus ; hardness ; lattice parameter ; mixing enthalpy

Scanning electron microscopy and energy-dispersive X-ray spectroscopy are employed to examine the phase transformations and morphology of ground KS37 alloy (with SmCo5 matrix) during solid hydrogenation, disproportionation, desorption, and recombination at 0.4 MPa hydrogen pressure and 950°C. The ground alloy has cellular microstructure. The disproportionation of the ground alloy leads to samarium hydride and cobalt with nanosized grains (35–100 nm). The morphology of the disproportionation products depends on reaction parameters. The desorption and recombination result in a nanosized Sm2Co7 phase with 40–75 nm grains and a partially nanosized SmCo5 phase with 45–140 nm grains. The mechanism whereby the nanostructure of ferromagnetic alloys forms through mechanical and heat treatment with hydrogen is explained. It is based on the variation in morphology during hydrogen-initiated phase transformations and dependences such as grain size of the disproportionation products versus grain size of the alloy before hydrogenation and grain size of the recombined alloy versus grain size of the disproportionation products.
Keywords: ferromagnetic alloys ; grinding ; hydrogen treatment ; hydrogenation ; disproportionation ; desorption ; recombination ; phase transformations ; microstructure ; nanostructure

The paper presents an overview of the centuries-old evolution of glass formulations, technologies, and applications throughout the history of civilization. We show the role of glass in works of art, in manufacture of housewares, as a transparent and translucent material in construction, and in applications such as optics and laser technology, reinforcement for composites, and transparent armor.
Keywords: glass ; amorphous state ; silicates ; opacifiers ; quartz ceramics ; transparent armor ; glassblowing techniques ; crystal glass ; smalt glass ; mosaics ; crown glass ; lead glass ; float process ; armor