Powder Metallurgy and Metal Ceramics (v.54, #11-12)

Analysing the Twist Extrusion of Porous Blanks Using Modified Theories of Plasticity for Porous Bodies by A. V. Kuz’mov; M. B. Shtern; E. G. Kirkova; Ya. E. Beygel’zimer; D. V. Pavlenko (631-640).
Features of the twist extrusion of blanks containing pores and plane cracks are considered. The effect of flat cracks on the porosity distribution and rate of local loosening during deformation is analyzed. The analysis is conducted using a modified theory of plasticity for porous bodies and the finite-element method. It is established that the porosity distribution is sensitive to the concentration of flat defects. At a certain concentration of plane defects, the porosity distribution is inverted: the porosity is higher at the periphery than at the center. The effect of flat defects on the accumulated strain and, as a result, on the structure refinement is less significant. It is confirmed that using the counter-pressure allows suppressing the growth of defects, reducing the refinement efficiency.
Keywords: plasticity of compressible materials ; twist extrusion ; severe plastic deformation ; powder consolidation

Chromium-containing steels must be sintered in dry atmospheres with low partial pressures of oxygen, such as nitrogen–hydrogen mixtures. The conventional endogas atmospheres have a potential to carburize the main steel and simultaneously oxidize alloying elements, e.g. Cr and Mn, preventing proper sintering. Fe–1.5% Mn–1.5% Cr–0.25% Mo–0.4% C steel is successfully sintered in flowing technical nitrogen by controlling the local microatmosphere, through the use of semiclosed container/getter/activator combinations. Then, the necessary reducing reactions are induced in the dry microatmosphere within and around the specimens. As manganese has a higher affinity for oxygen than chromium, chromium oxide is reduced by relying only on carbon and manganese in the semi-closed container. Mechanical properties of the specimens sintered in technical nitrogen do not significantly differ from those sintered in dry hydrogen.
Keywords: PM Cr–Mn steels ; mechanical properties ; sintering microatmosphere

Thermochemical Boriding of Fe–5% Cr Alloy by V. I. Dybkov (652-664).
Boriding of the Fe–5% Cr alloy in amorphous boron powder with KBF 4 as an activator at 850–950°C and reaction times of 3600–28800 sec results in the formation of two boride layers at the interface between the reagents. The outer layer bordering boron consists of the FeB phase, while the inner one adjacent to the alloy base consists of the Fe 2 B phase. The average chromium content of the FeB layer is 4.2 wt.% (2.7 at.%) and of the Fe 2 B layer is 4.5 wt.% (3.5 at.%). The formation of boride layers is sequential, rather than simultaneous. The Fe 2 B layer forms and grows first. The FeB layer does not show up until Fe 2 B reaches a necessary minimum thickness exceeding 100 μm, for example, at 850°C. The characteristic feature of both layers is a profound texture. Their diffusional growth kinetics is close to parabolic, x 2 = 2k 1 t. The temperature dependence for the growth rate constant of the Fe 2 B layer in the time range 3600–14400 sec, when the FeB layer still has not formed between boron and Fe 2 B, is described by an Arrhenius relation, k 1 = 7.0010 −6 exp(−135.0 kJ × × mol −1 /RT). The microhardness is 15.6 GPa for the FeB layer, 13.0 GPa for the Fe 2 B layer, and 0.87 GPa for the alloy base. The dry abrasive wear resistance of borided Fe–5% Cr alloy samples found from weight loss measurements is more than one order of magnitude greater than that of their base. Surface boride coatings may be employed in manufacturing products, parts, and materials for functional applications to enhance their service characteristics.
Keywords: thermochemical boriding ; Fe–5% Cr alloy ; boride layers ; microstructure ; chemical composition ; growth kinetics ; microhardness ; abrasive wear resistance

Structurization and High-Temperature Oxidation Resistance of U8A Steel with Ti–Cr–Al Multi-Component Diffusion Coatings by T. V. Loskutova; S. S. Levashov; V. G. Khizhnyak; I. S. Pogrebova (665-671).
The phase and chemical composition, structure, and microhardness of multi-component coatings produced by tetanizing (titanium) and titanaluminizing (titanium–aluminum) chemical vapor deposition (CVD) of U8A chromium steel are examined. Both titanizing and titanaluminizing were carried out in powder mixtures of titanium, aluminum, inert additive, and activators at 1050°C for 4 h. It is demonstrated that using the proposed saturation methods results in the formation of multilayer coatings of: (i) chromium and titanium carbides after titanizing; (ii) chromium and titanium carbides; titanium, aluminum, chromium, and iron intermetallides after titanaluminizing. A high concentration of iron, chromium, titanium, and aluminum is discovered on the external surface of the titanaluminized coatings. Both Fe and Cr can be provided by a chromium layer based on chrome carbides. It is demonstrated that the microhardness of multilayer coatings based on chromium and titanium carbides is 16–31.5 GPa and that based on chromium and titanium carbides and intermetallides is 5.8–36 GPa. It is established that, at a temperature of 900°C, the hightemperature oxidation resistance of titanium–chromium–aluminum coatings on U8A steel exceeds that of titanium, titanium–chromium, and chromium coatings.
Keywords: U8A steel ; diffusion coating ; chromizing ; titanizing ; titanoaluminizing ; high-temperature oxidation resistance ; oxidation ; microhardness

Co-based alloy modified with La2O3 is deposited by high velocity oxy-fuel (HVOF) spraying rocess. The microstructure, porosity, hardness, and abrasive wear of the coatings are investigated. The La2O3 addition refines the microstructure, forms new phases, and increases hardness and abrasive wear resistance of the modified coating. The abrasive wear behavior of these coatings is investigated under normal loads 5 and 15 N against 220 abrasive grit size. The abrasive wear is carried out using 30 and 50 m/min sliding rates. The abrasive wear is found to increase with the increase in normal load and sliding rates. Analysis of the worn surfaces by scanning electron microscope images revealed cutting and plowing as the material removal mechanisms in these coatings under abrasive wear conditions used in this research.
Keywords: HVOF ; La 2 O 3 ; hardness ; microstructure ; porosity ; abrasive wear

Gradient Laser ZrB2–MoSi2 Coating on Graphite by I. A. Podchernyaeva; O. N. Grigor’ev; D. V. Yurechko; A. M. Bloshchanevich; M. A. Vasil’kovskaya (679-685).
A high-temperature ZrB2–MoSi2 coating on graphite is produced by pulsed laser melting (in air) of a graphite sample with powder layers pre-deposited on the working surface. It is demonstrated that laser melting is accompanied by an intensive phase formation in the layers and at the interface. The main phases of the surface are: ZrB2, MoSi2, Mo5Si3, and ZrC. It is demonstrated that the coating forms with the liquid phase reinforced with ~1 μm thick fibers. It is characterized by a gradient change in the composition towards the substrate: the content of ZrC increases and the content of ZrB2 decreases towards the graphite substrate. Such a change in the composition leads to higher adhesive strength of the coating.
Keywords: laser coating; graphite; zirconium diboride; structure; composition

Alloy Constitution and Phase Equilibria in the Hf–Ru–Rh System. II. Liquidus Surface, Melting Diagram, and Vertical Sections of the Partial Hf–HfRu–HfRh System by L. S. Kriklya; K. E. Kornienko; V. G. Khoruzhaya; V. M. Petyukh; L. A. Duma; K. A. Meleshevich; A. V. Samelyuk (686-695).
According to the constitution of the solidus surface in the Hf–Ru–Rh system over the composition range 50−100 at.% Hf and the data obtained in studying the as-cast alloys by physicochemical analysis techniques, we constructed, for the first time, the liquidus surface of the partial Hf–HfRu–HfRh system on the composition triangle and its melting diagram. The vertical sections at 5 at.% Ru, 10 at.% Rh, and 75 and 80 at.% Hf at the ratio Ru : Rh = 1 : 1 are presented. The processes that occur when the alloys are crystallized are shown in the reaction scheme. The primary crystallization regions for a continuous series of solid solutions between isostructural (CsCl type) phases formed by the HfRu compound and its high-temperature modification (δ phase) as well as β-Hf and γ-Hf2Rh (Ti2Ni type) solid solutions are parts of the liquidus surface. An invariant four-phase equilibrium involving liquid, LU + δ ⇆ γ + <β-Hf>, is observed at 1373°C in the system.
Keywords: liquidus surface ; primary crystallization ; invariant equilibrium ; melting diagram ; vertical section

Calorimetric Study of the La2Hf2O7 Heat Capacity in the Range 57–302 K by A. R. Kopan’; M. P. Gorbachuk; S. M. Lakiza; Ya. S. Tishchenko (696-703).
The heat capacity of La2Hf2O7 has been studied in the range 57–302 K by adiabatic calorimetry. The heat capacity C p of lanthanum hafnate changes monotonically and there are no anomalies. The values of heat capacity, entropy, enthalpy, and reduced Gibbs energy have been determined in standard conditions: C p ° (298.15 K) = 229.39 ± 0.92 J · mol–1 · K–1, S° (298.15 K) = 246.9 ± 2 J × × mol–1 ∙ K–1, Ф° (298.15 K) = 114.76 ± 1.72 J ∙ mol–1 ∙ K–1, and H° (298.15 K)–H° (0 K) = 39403 ± 197 J ∙ mol–1. In the series of isostructural La2Zr2O7 → La2Hf2O7 compounds, atomic oscillation frequency in the lattice decreases and low-temperature heat capacity increases with greater mass of oscillator atoms from Zr to Hf.
Keywords: thermodynamics; heat capacity; enthalpy; entropy; reduced Gibbs energy; lanthanum hafnate

Thermodynamic Properties of Ce–In–Ni Ternary Alloys by M. I. Ivanov; K. Yu. Pastushenko; V. G. Kudin; V. V. Berezutskii; M. O. Shevchenko; V. S. Sudavtsova (704-711).
The mixing enthalpies of the liquid Ce–In–Ni ternary alloys have been determined by isoperibol calorimetry along three sections: (Ce0.4In0.6)1–xNix (0 < x < 0.11), (In0.15Ni0.85)1–xCex (0 < x < < 0.12), and (Ce0.21Ni0.79)1–xInx (0 < x < 0.03). The mixing enthalpies and activities of components in the Ce–In–Ni ternary alloys are calculated using various models, chosen by critical analysis. The data obtained previously for the binary subsystems are used for calculations, and new experimental data for the ternary systems are employed to verify the reliability of the models. The melts mix with release of significant amounts of heat, and the activities of their components are characterized by negative deviations from ideal solutions.
Keywords: mixing enthalpy; Ce–In–Ni system; thermodynamic properties; Redlich–Kister; Kohler; Toop models

Structure of Nb–Mo–B Alloys in the Nb–NbB–MoB–Mo Region and Phase Equilibria at Melting–Solidification Temperatures by O. A. Potazhevska; A. A. Bondar; L. A. Duma; V. B. Sobolev; T. Ya. Velikanova (712-724).
X-ray diffraction, metallography, and electron microprobe analysis are employed to study the Nb–Mo–B alloys in as-cast state and after annealing at subsolidus temperatures in the Nb–NbB–MoB–Mo region. The solidus temperatures are measured by pyrometry using the Pirani–Alterthum technique. The experimental data are used to construct the solidus and liquidus surfaces in the range up to 50 at.% B for the first time.
Keywords: Nb–Mo–B system ; phase diagram ; boride ; solidus ; liquidus ; eutectic

Superhard Vacuum Coatings Based on High-Entropy Alloys by V. F. Gorban’; R. A. Shaginyan; N. A. Krapivka; S. A. Firstov; N. I. Danilenko; I. V. Serdyuk (725-730).
High-entropy TiZrVNbTa, AlCrFeCoNiCuV, and TiZrHfNbTaCr alloy coatings with a thickness of 2.5–6 μm and with various phase compositions were deposited by dc magnetron sputtering. The chemical and phase composition of the TiZrVNbTa and TiZrHfNbTaCr coatings do not change substantially during deposition. Only when the substrate bias is higher than –180 V, the deposited AlCrFeCoNiCuV alloy coatings are depleted of Al and Cu. All the coatings are nanostructured, and their microhardness varies between 10 and 19 GPa, and reduced elastic modulus changes between 106 and 192 GPa depending on the phase composition.
Keywords: high-entropy alloy; magnetron-sputtered coating; microstructure; hardness; elastic modulus; phase composition

The methodology to determine the compressive strength of microspheres is improved. It is validated by buoyancy measurements. It is demonstrated that the tangent circle method allows determining the point of maximum curvature of the stress–strain curve of microspheres. The optimal ratio of the height of microspheres to the diameter of the die mold (H/D) is determined. Curves of variation of the elastic modulus and absorbed strain energy with the maximum cyclic stress are plotted.
Keywords: microsphere; strength; buoyancy; elastic modulus; absorbed energy

Thermally Activated Processes of the Phase Composition and Structure Formation of the Nanoscaled Co–Sb Films by R. A. Shkarban; Ya. S. Peresunko; E. P. Pavlova; S. I. Sidorenko; A. Csik; Yu. N. Makogon (738-745).
It is investigated the formation of the phase composition and structure in the nanoscaled CoSbx (30 nm) (1.82 ≤ x ≤ 4.16) films deposited by the method of molecular-beam epitaxy on the substrates of the oxidated monocrystalline silicon at 200°C and following thermal treatment in vacuum in temperature range of 300–700°C. It is established that the films after the deposition are polycrystalline without texture. With increase in Sb content the formation of the phase composition in the films takes place in such sequence as this is provided by phase diagram for the bulky state of the Co–Sb system. At annealing in vacuum at temperature above 450–500°C a sublimation not only of the crystalline Sb phase but from the antimonides occurs. This is reflected on the phase composition change by following chemical reactions: CoSb 2 → 600 ° C S b ↑ = CoSb , CoSb 3 → 600 ° C S b ↑ = CoSb 2 , CoSb 3 + S b ↑ → 600 ° C CoSb 3 $$ {mathrm{CoSb}}_2overset{600{}^{circ}mathrm{C}}{ o}mathrm{S}mathrm{b}uparrow =mathrm{CoSb},{mathrm{CoSb}}_3overset{600{}^{circ}mathrm{C}}{ o}mathrm{S}mathrm{b}uparrow ={mathrm{CoSb}}_2,{mathrm{CoSb}}_3+mathrm{S}mathrm{b}uparrow overset{600{}^{circ}mathrm{C}}{ o }{mathrm{CoSb}}_3 $$ and leads to increase in amount of the CoSb and CoSb2 phases and decrease in amount of the CoSb3. CoSbx (30 nm) (1.8 < x < 4.16) films under investigation are thermostable up to ~350°C.
Keywords: skutterudite CoSb 3 ; nanoscaled film ; sublimation ; phase transformation

Formation of TiO2/Mica Composite for Photocatalysis by M. Ozawa; H. Matsui; S. Suzuki (746-749).
The design results of the composites TiO2/mica photocatalytic active sheet are presented. For producing of initial powders elements of sol-gel and freeze-drying were used. The tape casting of TiO2/mica water slurry with using of doctor blade apparatus were used for forming of sheets. The phase composition, the specific surface area, the porous distribution and morphology of the produced powders and materials were investigated. It is established that the resulting TiO2 pillared mica sheet possesses good photocatalytic properties determined by gaseous acetaldehyde removal measurement.
Keywords: mica ; titanium dioxide ; tape casting ; acetaldehyde ; photocatalytic properties

The paper presents a historical evolution of compositions and applications of glazes on various ceramics (majolica, facing tile, glazed pottery, porcelain). The origin and development of artistic and industrial enameling processes for metals are described. The effect of additions in glazes and enamels on the color and transparency of decorative, artistic, and technical vitreous coatings on metallic and nonmetallic materials is exemplified by objects created in different historical epochs.
Keywords: glaze ; enamel ; opacifier ; frit ; slurry ; celadon ; underglaze and overglaze mineral paints ; artistic and technical enameling