Powder Metallurgy and Metal Ceramics (v.51, #3-4)

Variation in the particle size of FE–TI–B4C powders induced by high-voltage electrical discharge by O. N. Sizonenko; G. A. Baglyuk; A. I. Raichenko; É. I. Taftai; E. V. Lipyan; A. D. Zaichenko; A. S. Torpakov; E. V. Guseva (129-136).
The effect of high-voltage electrical discharge (ED) on the particle size of Fe–Ti–B4C powders in a hydrocarbon liquid is studied. It is shown that high-voltage ED allows significant refinement of the powders. The important factors are integral processing energy and pressure in the discharge channel. A relationship between the integral processing energy and decrease in the average diameter of micropowder particles is found. It is shown that the average particle size monotonically decreases up to a certain value of integral processing energy. The use of high-voltage ED for the refinement of micropowders permits significant reduction in time and energy needed to reach the desired particle size compared with other methods.
Keywords: high-voltage electrical discharge; pressure in the discharge channel; integral energy; powder; refinement; particle size; specific surface area

The potential use of a new-type mill developed at the Frantsevich Institute for Problems of Materials Science to produce copper and chromium powder mixtures intended for the manufacture of electrical-grade materials is studied. The mill ensures mechanical grinding of loose materials by mechanisms similar to those acting in vortex and jet mills. The greater powder refinement in this mill is due to the sliding interaction of particles with abrasive surfaces of the mill chamber. It is shown that common grinding of electrolytic copper and reduced or aluminothermic chromium for 10–30 min in argon promotes variation in the shape of particles, facilitates their mixing, and provides uniform distribution of components in the mixture.
Keywords: copper; chromium; grinding; shape of powder particles; quality of mixing

Effects of major impurity elements on compressibility of water-atomized iron powder by Songlin Li; Qiumin Yang; Jianmin Cui; Yong Yuan; Dejin Zhang; Yongliang Yu (142-149).
Compressibility is one of the most important properties of iron powder for powder metallurgy applications. Understanding effects of chemical impurity elements on compressibility of the iron powder and differentiating contribution of each impurity element are critical for the iron and steel powder enterprise to select approaches to control and improve compressibility of the powder. In this work 500 water-atomized iron powder samples are chosen and effects of the main impurity elements like C, Si, Mn, P, and S and hydrogen loss (HL) reflecting oxygen on compressibility of the iron powder are quantitatively studied. First, effect of single impurity element on the compressibility is investigated. Linear regressions show the degrees of regression are very low even with sample number increase up to 500 implying uncertainty of the single factor regressions due to the instable content of the other impurities when the effect of one impurity element is concentrated on. Then, a multiple factor regression is established taking into account all the six impurity elements as a whole. The degree of regression improves to as high as 0.9746 with sample number increase to 500 and dependency of compact density Y on the six impurity elements can be expressed as: Y = 7.1442 – 0.4231× C% – 0.0498 × Si% – 0.0988 × Mn% – 3.2784 × P% – 0.2577 × S% – 0.1220 × HL%. This equation manifests the negative effects of all the six impurity elements on compressibility of the water-atomized iron powder by P and C mostly, Mn, S, and HL moderately, and Si least.
Keywords: powder metallurgy; iron powder; compressibility; linear regression; impurity element

The hot forging of porous preforms in a closed die with a cone-shaped flash gutter is numerically simulated. The cross-sectional distribution of strains and density over the preform substantially differs at various stages of the process. The maximum axial and radial strains, as well as intermediate density values, are observed near the flash gap.
Keywords: hot forging; porosity; deformation; densification; numerical simulation

The compaction of fine charge material in the deformation zone of a roll press is described. Analytical expressions are provided that are used to study the effect of the configuration and size of shaping elements on the power and process parameters in briquetting of fine charge material in roll presses. The calculated data show that the rational power parameters of briquetting and the desired productivity can be ensured at the stage of press equipment design by varying the configuration of shaping elements.
Keywords: roll press; fine charge material; deformation zone; briquettes; power and process parameters

The paper analyzes the sintering of three types of calcium phosphate powders and S–B–Na glass powder under the same conditions. It is concluded that a liquid phase, represented by the glass melt, shows up when the glass is sintered with biogenic or synthetic hydroxyapatite or a mixture of synthetic phosphates. The substantial pore formation in the sintering process is mainly due to the removal of carbon oxides and water vapors resulting from glass charge decomposition and glass boiling. Parameters of grain and porous microstructures of the ceramics are shown before and after the primary and secondary sintering. The mechanical strength and biosolubility of the ceramic samples are reported as well.
Keywords: calcium phosphates; grain and pore microstructure; biosolubility

Magnetic materials in the form of colloidal nanoparticles have received much attention due to their remarkable magnetic proprieties, which are dominated by superparamagnetism; these materials being used in various technical and biomedical fields, including the preparation of stable magnetic fluids. Co-precipitation from metal salts solutions is a rather simple and available method, which was widely applied in the frame of our study and resulted in nanopowders of Mn x Zn1–x Fe2O4 (x = 0.9, 0.7, 0.5, and 0.3). Microstructural and magnetic investigations were carried out to reveal nanometric sizes of magnetic grain/nonmagnetic shell systems. Different dependences on the manganese fraction of the saturation magnetization, on one side, and crystallite size and magnetic coercivity, on the other side, were evidenced.
Keywords: mixed metal oxides; coated nanoparticles; magnetic properties

The effect of preliminary treatment of a steel substrate on the dynamic properties of cathode jets during electrospark deposition is studied. The energy of cathode jets is determined indirectly using the strain hardening of the electrode surface layer. It is established that the dynamic properties of cathode jets are determined by the electrode gap and structural and heat-transfer properties of the cathode material.
Keywords: electrospark deposition; cathode jets; substrate temperature; coating composition

Properties of Cu–Al–Mn shape memory alloy fibers produced by melt quenching by A. G. Kostornov; V. N. Klimenko; M. M. Serov; L. M. Neganov; M. M. Kozyrev (186-190).
The paper examines the vacuum-sealed melt quenching and the properties of Cu–12% Al–3.5% Mn shape memory alloy fibers. The average effective diameter of the fibers is 113 μm. The temperatures of martensite transformations are determined by resistometric technique. Significant grain refinement, from 0.75 mm (in the starting alloy) to 40 μm (in the fibers), is achieved by rapid melt quenching.
Keywords: Cu–Al–Mn; shape memory alloys; fiber; melt quenching

Effect of pressure–temperature treatment on the properties of antimony-doped tin dioxide by A. G. Gonchar; B. M. Rud’; A. I. Bykov; V. E. Shelud’ko; V. V. Kremenitskyi (191-197).
Compact samples are produced from antimony-doped tin dioxide in a high-pressure cell at a hydrostatic pressure of 4 GPa and a temperature of 873 K. Pressure–temperature treatment has resulted in a material exhibiting high density and hardness. Its electrical and physical properties are studied. The temperature dependence of resistivity shows that the test material is a degenerate semiconductor with low (1.5 meV) activation energy.
Keywords: sintering; pressure–temperature treatment; tin dioxide; resistivity; activation energy

Effect of electrospark deposition of Al–Si alloy on the wear resistance of a hard-alloy cutting plate by I. A. Podchernyaeva; D. V. Yurechko; A. V. Bochko; G. A. Sedlyar; L. M. Kostenko (198-203).
The electrospark deposition of AL25 aluminum alloy onto a VK8 cutting plate is studied to show the effect produced by the composition of a tribofilm formed in the cutting process on the wear resistance of the tool. The mass transfer kinetics, microstructure, composition, and microhardness of the deposited layer, and distribution of elements over the cutting edge surface after cutting are determined. It is shown that complex oxides that form on the cutting edge and are more chemically stable than volatile W and Co oxides increase the wear resistance of the tool by a factor of 1.5 to 1.8.
Keywords: spark-deposited coating; hard-alloy cutting plate; aluminum alloy; wear resistance

The Co–Ga–Si ternary system at 870 K by P. Ya. Lyutyi; A. O. Fedorchuk (204-208).
X-ray diffraction, structural, and metallographic analyses are employed to construct the isothermal section of the Co–Ga–Si ternary phase diagram at 870 K in the entire composition range. No ternary compounds form at the experimental temperature. A series of binary compounds are confirmed to exist. It is established that there are substitutional solid solutions based on CoSi and CoGa binary compounds. Their homogeneity ranges are determined.
Keywords: isothermal section; gallium; intermetallic compounds; crystal structure

Thermodynamic characteristics of SmAlO3 in the range 55–300 K by A. R. Kopan; M. P. Gorbachuk; S. M. Lakiza; Ya. S. Tishchenko (209-216).
The heat capacity of SmAlO3 is studied for the first time in the temperature range 60–300 K by adiabatic calorimetry. The values of heat capacity, entropy, enthalpy, and reduced Gibbs energy are determined in standard conditions: C o p (298.15 K) = 96.32 ± 0.39 J∙mol–1∙K–1; S o (298.15 K) = = 96.68 ± 0.77 J∙mol–1∙K–1; Φ o (298.15 K) = 44.34 ± 0.67 J∙mol–1∙K–1; H o (298.15 K) – – H o (0 K) = 15604 ± 78 J∙mol–1. It is assumed that the R—O bond strength (R is a rare-earth metal) influences the heat capacity of perovskite-type REM aluminates.
Keywords: thermodynamics; heat capacity; enthalpy; entropy; reduced Gibbs energy; samarium aluminate

High-temperature oxidation of ZrB2–SiC and ZrB2–SiC–ZrSi2 ceramics up to 1700°C in air by V. O. Lavrenko; A. D. Panasyuk; O. M. Grigorev; O. V. Koroteev; V. A. Kotenko (217-221).
The high-temperature oxidation of ZrB2–SiC and ZrB2–SiC–ZrSi2 ceramics up to 1700°C in air has shown their high corrosion resistance. A five-stage nonisothermal oxidation mechanism is established for the samples when heated at a rate of 20°C/min: 1) oxygen adsorption–desorption; 2) formation of ZrO2 and B2O3 oxides; 3) formation of α-SiO2 cristobalite and ZrSiO4 zircon; 4) formation of amorphous SiO2; and 5) formation of upper protective borosilicate film with ZrSiO4 inclusions at less than 40 wt.% SiC. It is shown that small ZrSi2 admixtures (<6–8 wt.%) substantially slow down the oxidation of the ceramics in initial heating stages due to diffusion-hindered formation of ZrO2 and B2O3. The 67.3 wt.% ZrB2–26 wt.% SiC–6.7 wt.% ZrSi2 ceramics are characterized by the highest corrosion resistance since their upper scale layer represents borosilicate glass stabilized with ZrO2 (tetragonal) inclusions.
Keywords: ceramics; high-temperature oxidation; oxidation products; borosilicate glass; kinetics and mechanism of process

Interaction of molybdenum with copper–silicon melts by V. V. Skorokhod; V. P. Titov; M. E. Golovkova; N. I. Filippov (222-228).
The solubility of molybdenum in copper–silicon melts and the kinetics of growth of Mo5Si3 and MoSi2 layers on the molybdenum–melt interface at 1200°C are studied. At 0.20–0.36 at. parts Si, the solubility of molybdenum in the melts is described by the following equation: lgX Mo = –2.587 + + (3.282)X Si. The dependence of the growth rate constants of the Mo5Si3 layer on the activity of silicon in the 9–15 wt.% Si melt is established: kMo–Si = –0.3806 + (65.191) aSi. It is shown that two phases form at 20 wt.% Si: Mo5Si3 and MoSi2. Their thicknesses are 29.8 ± 2.9 μm and 25.7 ± ± 2.8 μm, respectively. The time dependence of the Mo5Si3 layer growth rate in Cu–Si melts is established to obey a parabolic law. The melt composition in three-phase equilibrium Mo–Mo5Si– melt is found to be (at. parts): XSi = 0.147; XMo = 7.86∙10–3; the rest is copper. At 35 wt.% Si, only the MoSi2 phase is formed at the interface.
Keywords: molybdenum; silicon; melt; solubility; kinetics; layer growth; three-phase equilibrium

Low-temperature heat capacity and high-temperature enthalpy of LuSi by N. P. Gorbachuk; S. N. Kirienko; V. R. Sidorko; I. M. Obushenko (229-233).
The heat capacity and enthalpy of lutetium monosiliсide are measured for the first time in the temperature ranges 68.56–298.21 and 465–2191 K, respectively. The standard values and temperature dependences of the heat capacity, entropy, Gibbs energy, and enthalpy of the silicide are calculated in a wide temperature range. The temperature, enthalpy, and entropy of melting are determined.
Keywords: thermodynamics; enthalpy; heat capacity; entropy; Gibbs energy

The paper examines the phase mechanism and rates of TiCu, Ti3Cu4, and Ti2Cu3 interaction with hydrogen in the range 298–573 K at a hydrogen pressure of 1.0 MPa. The thermodynamic potential of TiCu direct and destructive hydrogenation and TiCu decomposition is established. The thermodynamic priority of destructive hydrogenation in the range 298–773 K is revealed. However, x-ray diffraction shows that only direct hydrogenation of TiCu, Ti3Cu4, and Ti2Cu3 proceeds in the range 298–373 K. The intermetallic compounds successively interact at 573 K with hydrogen through the formation of intermetallic hydrides (TiCuH1.19, Ti3Cu4H2.44, and Ti2Cu3H1.32) and their decomposition to titanium hydride and copper. These hydrides form more rapidly than decompose. It is established that mechanical destruction of the material occurs during direct hydrogenation.
Keywords: TiCu; Ti3Cu4 ; Ti2Cu3 ; phase mechanism; intermetallic hydrides; direct hydrogenation

Fractographic analysis of green compacts of metal powders by O. K. Radchenko; K. O. Gogaev; O. Yu. Koval; S. O. Firstov (243-252).
The paper examines the mechanisms that contribute to the strength of green compacts produced and tested in different thermal conditions (different homological temperatures of Sn, Zn, Cu, Ni, and Mo powders compacted and tested in normal conditions). The role of powder particle shape is demonstrated using scanning electron microscopy to analyze images of the particles and fracture patterns of the compacts. Partial plastic fracture is found only in the Sn powder sample. When plastic powders with irregular, branched particles (Cu, Ni) are compacted, the mechanism of adjusting particle surfaces to one another prevails and leads to all three mechanical components: interlocking, entangling, and seizing. When plastic powders with spherical particles are compacted, deformation of particles prevails. The ratio of the tensile strength of compacts (σb.i) determined indirectly to the tensile strength (σb) of particulate material shows a semilogarithmic dependence on the ratio of compacting pressure (P) to the yield stress (σ0.2) of the particulate material. The dependence of the ratio of σb.i to the elastic modulus on the homological temperature of compacting and testing divides into two linear dependences for spherical and nonspherical particles.
Keywords: metal powder; compact; fracture pattern; strength