Powder Metallurgy and Metal Ceramics (v.51, #9-10)

The results from simulation of equal-channel angular extrusion of sintered porous blanks with use of different deformation patterns are presented. It is shown that the maximum equidensity and the minimum volume of the poorly compacted area are observed in the pattern with a movable bottom plate of the die horizontal channel and with backpressure on the sample portion being extruded. This deformation pattern is also determined by the maximum values of deformation force.
Keywords: equal-channel angular extrusion; deformation; porosity; backpressure

Production of Titanium Powder Sheets by Asymmetric Rolling by K. A. Gogaev; V. S. Voropaev; G. Ya. Kalutskii; Yu. N. Podrezov; D. G. Verbilo; O. S. Koryak (509-517).
The influence of symmetric and asymmetric rolling on the formation and properties of titanium powder rolled sheets is studied. It is established that the asymmetric rolling of powder metal produces sheets with higher density and much better mechanical properties than symmetric rolling does. The effect of the titanium powder rolling conditions on the structure of the material before and after sintering is studied. The rolled metal obtained by asymmetric rolling has best mechanical properties at a sintering temperature lower by 200°C than that of symmetric rolling. The technological feasibility of asymmetric rolling of titanium powder is demonstrated.
Keywords: asymmetric rolling; powder; titanium, properties

Microstructure, Growth Kinetics, and Abrasive Wear Resistance of Boride Layers on Fe–30% Cr Alloy by V. I. Dybkov; V. R. Sidorko; L. V. Goncharuk; V. G. Khoruzha; A. V. Samelyuk (518-530).
Two boride layers are found to form at the interface between reacting phases in the course of boriding a Fe–30% Cr alloy in boron powder with KBF4 (activator) in the temperature range of 850–950°C and reaction times 3600–43200 sec (1–12 h). Each of these layers is single-phase structurally (crystallographically) and two-phase compositionally (chemically). The outer boride layer bordering boron consists of the crystals of the (Fe, Cr)B and (Cr, Fe)B compounds, while the inner layer adjacent to the alloy base comprises the crystals of the (Fe, Cr)2B and (Cr, Fe)2B compounds. The characteristic feature of both layers is a profound texture. Diffusional layer-growth kinetics are close to parabolic and can alternatively be described by a system of two non-linear differential equations dx/dt = (kB/x) – (rgkFe/py), dy/dt = (kFe/y) – (qkB/sgx), where x is the outer FeB layer thickness (m), y is the inner Fe2B layer thickness (m), kB is the FeB layer growth-rate constant (m2⋅sec–1), kFe is the Fe2B layer growth-rate constant (m2⋅sec–1), g is the ratio of the FeB and Fe2B molar volumes, p = q = r = 1, and s = 2 (factors from the chemical formulae of FeB and Fe2B). The temperature dependence of the layer growth-rate constants obeys a relation of the Arrhenius type K = Aexp (–E/RT), where K stands for any constant, A is the frequency factor, E is the activation energy, R is the gas constant, and T is the absolute temperature. Application of the least-squares fit method yielded the following equations: kB = 3.42⋅10–8⋅exp(–175.4 kJ × × mol–1/RT) m+⋅sec–1, kFe = 7.45⋅10–9 exp(–144.6 kJ⋅mol–1/RT) m2⋅sec–1. Microhardness values are 18.1 GPa for the outer boride layer, 15.2 GPa for the inner layer, and 1.75 GPa for the alloy base. The dry abrasive wear resistance of the outer boride layer, found from mass loss measurements, is more than 300 times greater than that of the Fe–30% Cr alloy base. Such a huge increase in wear resistance is due to the microstructure of boride layers having a peculiar regular arrangement of enhanced rigidity.
Keywords: Boriding; Fe–30% Cr alloy; boride layers, microstructure; chemical composition, growth kinetics; microhardness; abrasive wear resistance

Sintering of Porous Powder–Fiber Structures by V. V. Doktorov; A. F. Ilyushchenko; V. V. Mazyuk; A. L. Moroz; A. A. Shapoval; I. V. Shapoval (531-538).
Addition of fibers to a porous powdered-metal structure to reduce shrinkage is proposed and justified. A method to determine pressure that causes powder to shrink during sintering is developed. The pressure causing the shrinkage of a PMS-N copper powder (63–100 μm) is determined experimentally. The main patterns in sintering of powder–fiber structures are revealed.
Keywords: porous materials; sintering; powders; fibers; compositions; shrinkage; particle size; capillary structure; reinforcement

Thermochemical Treatment of Porous Materials Produced from Low-Carbon Steel Fibers by A. G. Kostornov; O. V. Kirichenko; V. N. Klimenko; A. K. Gaiduchenko; D. N. Brodnikovskii (539-546).
A starting material produced from St10 low-carbon steel fibers (40–100 μm in diameter) is subjected to different types of thermochemical treatment: solid-phase contact diffusion nickelizing followed by gas contact diffusion chromizing, carburizing, quenching, and tempering; solid-phase contact diffusion nickelizing followed by chrome-carburizing; gas high-temperature nitrocarburizing; contact gas boronizing. It is established that these types of thermal treatment increase the offset yield strength (σ0.2) of the material by a factor of 2 to 6.
Keywords: porous fiber materials; thermochemical treatment

The structurization of compacted Fe–Ti–B4C powder mixtures during reaction synthesis is studied. X-ray diffraction of the material synthesized at 1200°C shows the presence of TiC and TiB2 phases formed in the interaction of titanium with carbon and boron resulting from the dissolution of B4C particles in the liquid phase and the interaction of iron with boron. The reaction between titanium, iron, and carbon (boron) is accompanied by a significant exothermic effect confirmed by the presence of two exothermic peaks on the DTA curve at 1085°C (corresponding to the eutectic formed in the Fe–Ti system in the interaction of respective mixture particles on contact surfaces) and 1236°C (resulting from the formation of titanium diboride and carbide particles from the liquid phase).
Keywords: thermal synthesis; carbide steel; carbide; titanium diboride; exothermic reaction; sintering; structurization; phase composition

The strength and plasticity of a series of rapidly solidified high-temperature aluminum alloys determined in tensile tests are analyzed over a wide temperature range. The properties of the following systems are studied: Al–Fe–Ce, Al–Fe–Cr–(TM), Al–Cr–Zr(Mn), and Al–Fe–V(Mo)–Si. The effect of the doping content and rapid solidification technique on strength is examined. The best samples of green products show 550–600 MPa strength at room temperature and at least 200–250 MPa at 300°C. The strength of Al–Fe–Cr–(TM) alloys with a high volume content of quasicrystals is approximately 100 MPa higher at 20 and 300°C, while their elongation is 50 to 67% lower than the corresponding characteristics of other materials.
Keywords: high-temperature aluminum alloys; rapid solidification technique; intermetallic phases; strength, elongation, doping with transition metals

Effect of the Silicon Introduction Method on the Structurization of Sintered Fe–Si–C and Fe–Si–B–C Steels by G. A. Baglyuk; S. G. Napara-Volgina; L. N. Orlova; V. K. Kud; V. B. Deimontovich; A. N. Gripachevskii (566-571).
The methods to introduce silicon into Fe–Si–C and Fe–Si–B–C powder composites and its distribution in the alloy matrix are studied. Two types of silicon-containing additions, such as silicon carbide and low-carbon ferrosilicon, may be used. Silicon carbide promotes more uniform distribution of silicon in the iron matrix of the composites, while ferrosilicon leads to better compaction. Selective doping of individual phase components of the Fe–Si–B–C alloys is established: in particular, silicon diffuses only in the iron matrix and does not interact with the boron eutectic.
Keywords: composite; silicon carbide; boron carbide; ferrosilicon; carbon

Effect of Y2O3 and SiO2 additions on the phase formation and properties of the hot-pressed boron carbonitride composite by M. S. Kovalchenko; T. V. Dubovik; A. O. Rogozinska; M. D. Bega; V. I. Subbotin; T. P. Grebenok; O. P. Portnov (572-576).
The dependence of phase composition and properties of the BCN composite with additions of Y2O3 and SiO2 (quartz glass) on hot-pressing temperature is studied. It is established that new strengthening phases form with the composite during reaction pressure sintering. The optimum conditions for producing the BCN composite are found. The BCN composite has high thermal strength, oxidation resistance, and electrical insulating properties.
Keywords: boron carbonitride; yttrium oxide; quartz glass; hot pressing; phase formation; composite

Behavior of the submicrocrystalline Y–TZP–Al2O3 composite in dry friction with steel by N. L. Savchenko; T. Yu. Sablina; A. G. Melnikov; S. N. Kul’kov (577-583).
The paper discusses the wear resistance, friction coefficient, and structure of friction surfaces of submicron crystalline Y–TZP–Al2O3 composite rubbed against a steel disk counterface at a pressure of 5 MPa in a range of sliding speeds from 1 to 20 m/sec. It is shown that, starting at 2 m/sec, the friction surface is subdivided by a crack network into separate regions within which local spalling occurs at the maximum wear rate and a sliding speed of 5 m/sec. X-ray diffraction reveals inversion (with respect to the initial state) of the peak intensities of the tetragonal phase with random crystalline grain orientation. The degree of this inversion increases with sliding speed. These results are discussed in terms of the effects exerted by the reorientation of martensite-free deformation twins in the tetragonal phase and the formation of a quasi-liquid film on the wear resistance of Y–TZP–Al2O3.
Keywords: texture; ceramics; high-speed sliding

Phase interaction between ZrB2–SiC composite ceramics and oxide melts by O. N. Grigor’ev; A. D. Panasyuk; A. V. Koroteev; T. V. Dubovik (584-588).
The paper studies the mechanism of interaction between ZrB2–ZrSi2–SiC composites and dross-type oxide melts formed during the combustion of low-reactive carbons containing oxide rocks up to 30–40 vol.%. It is established that silicon carbide from the surface layer of the composite interacts with iron oxides to form spherical precipitates of the FeSi x phase at 1350–1550°C in the wetting process and in contact with the dross during 10–50 h. At the composite–dross interface, a thin (~7.5–30.0 μm) layer of ZrO2 and SiO2 oxides forms (depending on the amount of SiC and ZrSi2) and serves as a protective film preventing the composite ceramics from corrosion in the oxide melts. The optimum composition of the ZrB2–ZrSi2–SiC ceramics that can be used as corrosion-resistant in oxide melts is determined.
Keywords: ZrB2–ZrSi2–SiC composite ceramics; low-reactive carbons; contact interaction; iron silicide; spherical precipitates

Effect of aluminum, chromium, and iron doping on the heat resistance of zirconium by N. P. Brodnikovskii; I. V. Oryshych; T. L. Kuznetsova; N. E. Poryadchenko; N. A. Krapivka (589-593).
The influence of aluminum, chromium, and iron doping on the heat resistance of zirconium is studied. It is shown that a dense oxide film starts forming in the oxidation of the alloy containing 8 wt.% aluminum at 700°C regardless of its phase composition and ensures high heat resistance. At lower temperatures, to achieve the heat resistance comparable with that of the É110 commercial alloy, the content of the Zr–Al solid solution based on α-Zr, which should not contain more than 4 wt.% Al, is to be minimum. Additions of 1% Cr and 1% Fe can be used to strengthen the Zr–8Al alloy without a significant decrease in its heat resistance.
Keywords: heat; resistance; zirconium alloys; aluminum; chromium; iron; doping

Isothermal sections of the Al2O3–HfO2–Er2O3 phase diagram at 1250 and 1600°C by Ya. S. Tishchenko; S. M. Lakiza; V. P. Red’ko; L. M. Lopato (594-601).
The isothermal sections at 1250 and 1600°C for the Al2O3–HfO2–Er2O3 phase diagram are constructed for the first time. Phase equilibria are established at these temperatures; they are determined by the most thermodynamically stable compound, HfO2. No ternary compounds or appreciable solid-solution regions based on components or binary compounds are found in the ternary system. The presence of AL + F, Er3A5 + F, ErA + F, and Er2A + F two-phase regions on the isothermal section at 1650°C suggests that they contain triangulating sections of the Al2O3–HfO2–Er2O3 ternary system.
Keywords: ceramics; hafnia; alumina; erbia; interaction; isothermal section; phase diagram; eutectic materials

The heat capacity components for some rare-earth monosilicides experimentally studied in the range of middle and high temperatures are analyzed. Patterns of variation in temperatures and enthalpies of melting in a series of compounds from LaSi to LuSi are established. An equation is proposed to determine the high-temperature heat capacity Cp. The melting enthalpies and entropies are calculated for eight LnSi compounds that are still to be experimentally studied (Ln = Ce, Nd, Pm, Sm, Tb, Dy, Ho, Tm).
Keywords: thermodynamics; enthalpy; heat capacity; entropy; rare-earth silicides.

The paper examines the dependence of the secondary microstructure and electromagnetic parameters on the heat-treatment conditions of ferrite elements in the Mg–Mn–Zn–Ca–Fe–O system used in switching and logic elements. An optical microscope revealed dotted and netted secondary microstructures. The dotted structure is found in the samples sintered at 1603 K, quenched at 1273 K, and additionally annealed at 823 K. It is shown that annealing for up to 3 h increases the coercivity H, without degradation of the other parameters. This made it possible to increase the cyield of elements by a factor of 1.5 by increasing the Hc of rejected (because of low coercivity) elements. We developed a technique that provides equal temperature–time conditions for all annealed samples in a lot and allows controlling the yield of elements by periodically adjusting the annealing duration based on inspection of samples from inspection lots.
Keywords: ferrite; spinel structure; crystal lattice; magnetic element; sintering; hardening; annealing; secondary microstructure; electromagnetic parameters; output of accepted elements

Use of complex composite modifiers from rolled powder materials by S. M. Voloshchenko; K. A. Gogaev; V. V. Nepomnyashchii; M. G. Askerov (615-620).
Rolled complex composite modifiers have been tested and compared with conventional modifiers (most often used for the production of castings from high-strength iron) to reveal that the former have better plasticity. The effect of modifies produced with different methods but using components with close composition on the structure and mechanical properties of high-strength iron with spherical graphite is established. There are also results of field tests for cast plowshares made of bainite high-strength iron using rolled modifiers.
Keywords: modifiers; high-strength cast iron; thermal treatment; field tests