Powder Metallurgy and Metal Ceramics (v.55, #11-12)

The Effect of Compacting Rolling on the Properties of Titanium Powder Mill Products by K. A. Gogaev; V. S. Voropaev; Yu. N. Podrezov; Ya. I. Yevych; A. Yu. Koval’ (633-639).
The effect of deformation stress on the consolidating of titanium powder strips obtained by symmetrical and asymmetrical rolling is analyzed. It is determined, that the strength of green strips after asymmetrical rolling is substantially higher than that of conventional strips: for low and medium deformation stress (by a factor of 3–5) and for high deformation stress (by a factor of >10). The repeated rolling improves the mechanical properties of sintered strips. Titanium powder strips produced through optimal asymmetrical rolling possess better mechanical properties than conventional titanium strips.
Keywords: titanium powder; asymmetrical rolling; mechanical properties; fracture mechanisms

The migration of the boundary layer of lubricant into a porous briquette during compacting is investigated. It is found out that the density of briquettes compacted of a mixture of iron and graphite powders with the addition of animal fat hardly increases with increasing holding under the load, while the ejection pressure increases substantially. It is assumed that the ejection pressure increases due to the infiltration of a lubricant (from the layer between briquette and die wall) into the pores of the briquette. This leads to thinning disrupting the continuity of the lubrication layer and, accordingly, to increasing the external contact friction. The conducted studies allow not only predicting the behavior of viscous lubricants, but also enhancing the possibilities of impregnating the briquettes sintered under high pressure in the die in vacuum.
Keywords: pressing; lubricants; infiltration; pores; briquettes; friction

The Formation of ZrO2–Ti Composites by Spark Plasma Sintering by P. Lada; A. Miazga; J. Wozniak; K. Konopka; A. Olszyna (644-649).
The preliminary analysis of the ZrO2–Ti composite is conducted. The samples are prepared from the nanosized ZrO2 powder stabilized with 3 mol.% Y2O3 and 10 vol.% Ti powder with particles ~15 μm in size. The samples are formed by spark plasma sintering. The spark plasma sintering parameters are: temperature 1350°C, pressure 20 MPa, and duration 10 min. All process is carried out in argon. The density of the sintered ZrO2–Ti composites is determined by the Archimedes method. The microstructural characterization is carried out using X-ray diffraction and a scanning electron microscope. Additionally, the hardness and fracture toughness are measured. The obtained composite samples have a density of ~98–99% of the theoretical value. The homogenous distribution of titanium in zirconia matrix is SEM-confirmed. Moreover, the existence of a new phase in the Ti–Zr–O system is revealed by the X-ray diffraction analysis.
Keywords: zirconium oxide; titanium; spark plasma sintering; cermet composites

Boriding of Chromium Steels by V. l. Dybkov (650-655).
Two boride layers, having different kinds of microstructure, are formed on the surface of industrial chromium steel (13 and 25% Cr) samples during their boriding at 850–950°C and reaction times 3600–43200 sec (1–12 h). In the case of 13% Cr steel, the outer layer bordering boron consists of the FeB phase, whereas the inner adjacent to the solid substrate consists of the Fe2B phase. Each layer is a homogeneous phase. It is a microstructure of the first kind. With 25% Cr steel, each of the boride layers is two-phase. The outer layer comprises the FeB and CrB phases, while the inner the Fe2B and Cr2B phases. It is a microstructure of the second kind. Both boride layers on both steels are characterized by a profound texture. The strongest reflections are {002} and {020} for the FeB phase and {002} for the Fe2B phase. The growth rate of boride layers obeys a parabolic relation. Boride coatings with the microstructure of the second kind exhibit a much higher dry abrasive wear resistance than those with the microstructure of the first kind. The ratio of wear resistance of the outer boride layer on 13% Cr steel to that of the steel base is around 10. For 25% Cr steel, this ratio exceeds 250.
Keywords: chromium steel; boride layer; microstructure; phase composition; chemical composition; growth rate; microhardness; wear resistance

Low-Coercivity Precision Thermomagnetic Materials: Production, Properties, and Application in Engineering (Review) by Ya. A. Sytnyk; V. A. Maslyuk; S. B. Kotlyar; O. M. Bloshchanevich; A. I. Stegnii (656-664).
Modern low-coercivity thermomagnetic materials used in electrical engineering, electronics, and tool engineering are reviewed. They are primarily for the manufacture of magnetic shunts, magnetic secondary resistances, and temperature-sensitive elements for relays, whose response time is determined by the temperature near the Curie point). The effect of alloying additives (Mo, Cr, Cu) on the magnetic properties, heat treatment, and properties of structural changes in iron–nickel alloys is considered. The advantages of new thermomagnetic powder materials in comparison with cast alloys are demonstrated. Also, the prospects of their application in electrical engineering are considered.
Keywords: thermomagnetic material ; relays ; iron–nickel alloys ; alloying ; magnetic shunt

The ternary boride based cermets Mo2FeB2 were fabricated successfully with Mo, FeB, Fe, Cr and Ni mixed-powders by mechanical ball milling and reaction boronizing sintering. The results indicate that, there is no alloying reaction between powders during milling; at milling times from 4 to 24 h, the morphology of mixed-powder becomes finer and the distribution becomes more and more uniform; however, as milling time exceeds 24 h, the morphology and distribution have no obvious change. The bulk Mo2FeB2 can be fabricated with sintering temperature increasing from 1437 K to 1517 K. The relative density, the hardness and bending strength increase with the temperature increasing from 1437 to 1477 K; however, the relative density has no obvious change and the hardness, bending strength decrease with the temperature exceeding 1477 K. The result also indicates that, when the sintering time increases from 25 to 50 min, the relative density, the hardness and bending strength of sample increase; however, the relative density has no obvious change and the hardness, bending strength decrease with the time exceeding 50 min.
Keywords: mixed-powders; milling; reaction boronizing sintering; Mo2FeB2-based cermets; properties

Kinetics of Shrinkage, Structurization, and the Mechanical Characteristics of Zirconium Boride Sintered in the Presence of Activating Additives by O. N. Grigoriev; V. B. Vinokurov; T. V. Mosina; L. M. Melakh; N. D. Bega; A. V. Koroteev; L. I. Klimenko; A. V. Stepanenko (676-688).
Compaction kinetics, structurization, and mechanical characteristics of ceramics based on zirconium boride during the combined addition of sintering activating carbon additives, tungsten boride, and zirconium and tungsten silicides into the system are investigated. It is shown that the efficient additives for ZrB2 ceramics are tungsten silicide and boride, which allow not only reducing the sintering temperature and activating the ceramic compaction, but also provide the maximum strength of the samples. The shrinkage of activator-free ZrB2 occurs in the restructuring of boride that sinters with the formation of an azimuth texture. It is established that these processes do not occur in the ceramics sintered with activators. When such processes are developing, the sintering occurs under the conditions of intensive grain-boundary phase interactions. The mechanical characteristics are studied mainly by the indentation method with the determination of a certain number of ceramic strength characteristics. The differences in the characteristics of ceramics produced by hot pressing in vacuum and by hot pressing in the CO–CO2 atmosphere are studied. It is established that the grain-boundary strength of forming materials and their defective state show the greatest differences. The data obtained allow optimizing the production, composition, and structure of ceramics to ensure the necessary mechanical characteristics (compressive strength, tensile strength, bending strength, hardness, and fracture toughness).
Keywords: kinetics of shrinkage; sintering activators; mechanical characteristics; zirconium boride; structurization

High-Temperature ZrB2-Based Coatings on Metallic Alloys Produced by High-Velocity Air-Fuel Thermal Spraying by I. A. Podchernyaeva; O. N. Grigoriev; A. D. Panasyuk; Yu. I. Evdokimenko; V. M. Kisel’; D. V. Yurechko; V. M. Panashenko (689-697).
The composition and structure of ZrB2-based coatings with MoSi2, SiC, and AlN additions on metallic alloys produced by high-velocity air-fuel thermal spraying are studied. The use of composite powders with a low content of the NiCr binder (≤10 wt.%) is shown to be beneficial due to intensive adhesive interaction of the components. The phase transformations induced by high-temperature thermodynamically nonequilibrium processes, including oxygen-assisted ones, occur when the coatings are being formed. The coatings with a hardness of ~15 GPa and a porosity of ≤4% are characterized by a granular structure without cracks and have a 50–120 μm thick ceramic layer and an interfacial layer of uniform width (~10 μm) at the boundary between the NiCr alloy and stainless steel.
Keywords: thermal spray coating; zirconium diboride; structure; composition; properties

Isothermal Sections of the Al2O3–TiO2–Y2O3 Phase Diagram at 1550 and 1400°C by Ya. S. Tishchenko; S. M. Lakiza; V. P. Red’ko; O. V. Dudnik (698-706).
The isothermal sections of the Al2O3–TiO2–Y2O3 phase diagram are constructed for the first time at 1550 and 1400°C. New phases or appreciable homogeneity ranges based on components and binary compounds are not found in the ternary system. Triangulation of the system is determined by the Y2T2O7 phase, which is in equilibrium with compounds Al2TiO5, Y3Al5O12, YAlO3, and Y4Al2O9 and components TiO2 and Al2O3. The system is triangulated into six secondary triangles, in which three-phase eutectics are expected to exist. In five quasibinary sections, two-phase eutectics are likely to exist.
Keywords: ceramics; titania; alumina; yttria; interaction; isothermal section; phase diagram

Thermodynamic Properties of Iron Melts with Titanium, Zirconium, and Hafnium by P. G. Agraval; L. A. Dreval; M. A. Turchanin (707-716).
The literature data on the enthalpies of mixing and thermodynamic activities of Fe–Ti, Fe–Zr, and Fe–Hf liquid alloys are summarized. It is shown that the thermodynamic properties of these systems are characterized by significant negative deviations from the ideal behavior. In the framework of the associated solution model, the composition and temperature dependences of the thermodynamic functions of mixing for the Fe–Ti, Fe–Zr, and Fe–Hf systems are described. The temperature dependence of the thermodynamic properties of the considered systems is characterized by increase in negative deviations from the ideality with decreasing temperature and increasing thermodynamic stability of supercooled melts. Analysis of the degree of short-range order in the system melts, estimated as the total mole fraction of associates Σxass at the glass transition temperature, allows us to successfully interpret the known composition ranges of glass transition for the Fe–Zr and Fe–Hf melts and predict the composition range of glass transition for the Fe–Ti melts.
Keywords: enthalpy of mixing; thermodynamic properties; alloys of iron with titanium; zirconium; and hafnium; ideal associated solution model; amorphous alloys

Thermodynamic Properties of La–Ni Alloys by P. M. Subotenko; V. G. Kudin; M. O. Shevchenko; M. I. Ivanov; V. V. Berezutskii; V. S. Sudavtsova (717-725).
The mixing enthalpies of the La–Ni binary liquid alloys are determined by isoperibol calorimetry in the composition range 0 < x Ni <0.45 at 1430 K and 0.75 < x Ni < 0.80 at 1800 K. The thermodynamic properties of the La–Ni binary liquid alloys are calculated for the entire composition range using the model of ideal associated solutions and reliable published data. The thermodynamic activities of components show negative deviations from the ideal behavior; the mixing enthalpies are characterized by exothermic effects. The minimum mixing enthalpy of the melts is –28.0 ± 0.2 kJ/mol at x Ni = 0.6.
Keywords: isoperibol calorimetry; mixing enthalpy; La–Ni system; model of ideal associated solutions; thermodynamic activities

Simulation of the Microgravity Effect on Wettability of Solids with Different Liquids by Yu. V. Naidich; I. I. Gab; T. V. Stetsyuk; B. D. Kostyuk (726-731).
The dependence of contact angles on gravity in conditions simulating reduced gravitational force is studied. The contact angles for various solid–liquid systems are measured using both lowtemperature liquids (water, glycerin, hyposulfite, phosphoric acid) and metal melts (tin, silver). It is found that gravity has no effect on the contact angle when solids are wetted by liquids. The final answer to the question how gravity influences the contact angle can be given after experiments performed in conditions of a space station.
Keywords: microgravity; wetting; solid; liquid

A bulk sample of composition 51.9Fe11.1Mo26.3Cr10.7C (at.%) with β-Mn structure is prepared and examined by X-ray diffraction, high-temperature differential thermal analysis, and light microcopy. The stable high-temperature π phase of β-Mn type crystallizes congruently from the liquid phase in the Fe–Mo–Cr–C system, the singular point being found at about 51.9Fe11.1Mo26.3Cr10.7C at.% and 1520 ± 25 K. The structural characteristics of the π phase are presented. Its thermal expansion coefficient is 14.32 · 10–6 K–1 and microhardness 15.9 GPa. The π phase is characterized by high chemical resistance to inorganic acids and their mixtures from room temperature up to the boiling point.
Keywords: β-Mn structure; congruent crystallization; Fe–Mo–Cr–C system; thermal expansion coefficient; microhardness

Studying the Kinetics and Mechanism of Crystal Growth on Tungsten Wires in Normal Conditions by M. S. Shkoropado; S. G. Orlovskaya; Yu. A. Shevchenko (739-744).
The formation and growth of crystalline structures on the surface of tungsten wires at normal pressure in air are studied. It is found that crystalline structures are formed on the oxidized tungsten wires at 980 K. Their shape changes from whiskers to dendrites with increasing temperature during oxidation. The longitudinal and transversal growth rates of the structures are determined. The mechanism of formation and growth of oxide crystals on tungsten wires at high temperatures is proposed. It is proved that carbon atoms on the surface of a tungsten wire are nuclei for WO3 crystallization from the gaseous phase.
Keywords: tungsten; tungsten oxide; oxidation kinetics; mechanism of crystal growth; fractal

Effectiveness of Jet Milling for Producing Superfine Powders from Blast-Furnace Slag by V. P. Kravchenko; G. A. Baglyuk; A. I. Trotsan (745-750).
The paper examines the effect of ball (drum) grinding and jet milling on the particle size distribution and specific surface area of the powders produced from blast-furnace slag. The effectiveness of jet milling, providing relatively equal powder particles (more than 85% of the fractions is 0–10 μm in size), is shown. Decrease in the average particle size leads to greater specific surface area of the powder and to a sharp increase in activity (strength of the samples prepared with use of blastfurnace slag). Hydraulic activity σ ≥ 30 MPa can be reached by the powder produced from slag with an average particle size to 12 μm and specific surface area S = 0.6–0.8 m2/g, which increases the sample strength. The strength of cemented compositions based on blast-furnace slag can be improved to 40–43 MPa by adding 15–20% Portland cement to the starting mixture.
Keywords: blast-furnace slag; powder; grinding; particle size; specific surface area; hydraulic activity; binding properties