Damping properties of sintered high-porosity materials based on powders and discrete copper fibers

Experimental relationships are established between the vibration decrement and the level of maximum cyclical deformations during the bending of sintered high-porosity materials based on powders and discrete copper fibers. The quality of interparticle contacts is evaluated in the sintered materials. Comparison of curves of the vibration decrement versus porosity for fixed maximum cyclical deformations indicated that the vibration decrement of all materials decreases with increasing porosity (within the range from 40 to 77%); however, it is appreciably greater vibration decrement of the matrix material (compact copper). Sintered high-porosity materials based on discrete copper fibers have the highest indicators of energy dispersion, especially at relatively high levels of maximum cyclical deformations as compared with sintered materials based on copper powders.     

Antimony activities in copper mattes

A mass spectrometric technique combined with a double Knudsen cell was used to determine the antimony and copper activities in the Cu-Sb binary system at 1373 K and in the two-melt composition range of the Cu−S−Sb ternary system at 1423 K. The antimony and copper activities were calculated based on the intensity ration of the gaseous Sb and Cu species, over the unknown and known activity samples, respectively. γ _Sb ^o were found to be 1.1×10⁻² in molten copper at 1373 K, and 1.8×10⁻² and 0.44 in a copper-rich phase and in a matter phase, of the Cu−S−Sb ternary system at 1423 K, respectively. These values indicate, that antimony can be removed during the matte smelting and slagging stage of the copper smelting process. Interaction parameters of antimony in molten copper slagging stage of the copper smelting process. Interaction parameters of antimony in molten copper at 1423 K were calculated and found to be 10.7, −5.4, and 6.3 for ε _Sb ^Sb · ρ_Sb ^Sb, and ε _Sb ^S , respectively. M. HINO, formerly Visiting Scientist at the University of Toronto     

Wetting of a TBC-type hard alloy by some liquid metal melts

Wetting and contact interaction of (TiC−Mo₂C)−(Ni−Mo) cemented carbides by molten copper, nickel, iron and their alloys and also by the cupronickel alloy, cast iron, and steel melts is investigated. The results show that good wetting and intensive interfacial interaction for the cemented carbides in question was observed in the case of iron and nickel, their alloys with copper, cast iron, and steel. These materials are recommended for metallic binders in the preparation of composite materials—based on tungsten-free hard alloy. Deceased. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 98–101, January–February, 1999.     

Thermodynamic properties of liquid copper-lead alloys

Activities of lead in liquid copper-lead alloys were measured in the temperature range 1000 to 1200 °C at intervals of 50 °C by the dew-point technique. Various partial and integral molar properties of the liquid alloys were evaluated from the data, and the boundaries of liquid immiscibility in the Cu-Pb phase diagram were calculated. The activity coefficients of lead and copper in dilute solutions are represented by: In γ^o _Pb = (346/T@#@) + 0.181, and In γ^o _cu = (3852/T) − 0.945. The temperature dependence of Gibbs energy self-interaction coefficients for lead and copper are given by: ε^Pb _Pb = − (7828/T) − 3.506, and ε^Cu _Cu = − (8804/T) + 3.140. Various coefficients have the following values at 1200 °C: γ^o _Pb = 12.58,ε^Pb _Pb = − 8.85.η^Pb _Pb = − 52,197 J/gfw, σ^Pb _Pb = 38.15 J/gfw-K, γ^o _Cu = 5.31, ε^Cu _Cu = −2.92,η^Cu _Cu = − 63,970 J/gfw, and σ^Cu _Cu = 19.19 J/gfw-K.     

High-temperature oxidation of composite AlN-ZrB2-ZrSi2 ceramics

The high-temperature (to 1450°C) oxidation of AlN-ZrB₂-ZrSi₂ powders and compact ceramic materials with different contents of ZrB₂-ZrSi₂ solid solution in air is examined using scanning electron microscopy and differential thermal, thermogravimetric, x-ray phase, and x-ray spectrum microanalyses. It is established that the hot-pressed (practically porousless) ceramic materials have high corrosion resistance up to 1350–1400°C when scale components (individual oxides) interact with each other to form solid solutions based on aluminum oxide, zirconium oxide, and aluminum borate. These phases become sintered in the presence of the liquid B₂O₃ phase, self-reinforced scale being formed. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 196–203, 2008.     

Effect of chemistry and particle size of cryochemical powders on the properties of humidity sensors

A comparative analysis of various sintered materials based on cryochemical powders was carried out. The electrical resistance of compacts of pure aluminum oxide and its mixtures with CoO, MgO, ZrO₂, and Y₂O₃ were compared with data on the specific surface area, phase composition, and pore size distribution in the sintered ceramics. Conclusions were drawn about the suitability of the materials as humidity sensors. Highest sensitivity was found in sensors based on aluminum—cobalt spinel, and aluminum—magnesium spinel mixed with zirconium oxide. Deceased. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(400), pp. 39–43, March–April, 1998.     

Temperature effect on bending strength of hot-pressed boron carbide materials

The paper examines three groups of samples based on B₄C and B₁₃C₂ powders (with additions of Al and Al₂O₃ in the amount of 2 and 5 wt.%, respectively). It is established that the maximal strength (445 MPa) is characteristic of the material B₁₃C₂ over the whole temperature range. It does not change up to 1600°C. The increase in strength of B₄C-based samples is revealed over the range of 1200 to 1600°C, mainly for high-porous materials (10–12%). Presumably, this is due to the higher relaxation properties of porous material microstructure. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 60–68, 2007.     

The Normal spectral emittance of yttrium,lanthanum, cerium,praseodymium and neodymium above 1000 K

The normal spectral emittance (X = 0.645 μm) of yttrium, lanthanum, cerium, praseodymium and neodymium was determined at temperatures above 1000 K in an argon atmosphere at a pressure slightly above atmospheric. The measured normal spectral emittances are: yttrium, (solid), ε _nλ = 0.368 ± 0.005; (liquid), ε _nλ = 0.368 ± 0.005; lanthanum, (solid), ε _nλ = 0.409 ± 0.049; (liquid), ε _nλ = 0.257 ± 0.015; cerium, (liquid), ε _nλ = 0.309 ± 0.020; praseodymium, (solid), ε _nλ = 1.609 - 1.0964 x 10⁻³ T (K); (liquid), ε _nλ = 0.284 ± 0.005; neodymium, (solid), ε _nλ = 1.090 - 5.6 x 10⁻⁴ T (K); (liquid), ε _nλ = 0.394 ± 0.007. Formerly NSF Presidential Intern and PostDoctoral Fellow Formerly Undergraduate Research Helper, Prepared for the Energy Research and Development Administration under Contract No. W-7405-eng-82.     

Erosion of fiber reinforced Ai-4 pet CU composites

Erosion tests were carried out on a series of Al-4 pct Cu metal matrix composites containing up to 30 vol pct alumina fibers. The erosion rates were found to increase significantly with increasing fiber content. Analysis of the shift of low-angle impact erosion rate data suggests that increasing fiber content imposes ductility constraints for the deformation mechanisms operative during the erosion and impact process. SEM observations on eroded surfaces support this view. Tensile tests on the same materials also showed strong ductility constraints as a result of fiber additions. The erosion rates could be correlated inversely with the parameter σ_m ε_f obtained from tensile tests where σε_m is the maximum stress in the sample before failure and ε_f is strain to fracture. Hardness alone was not a suitable parameter for correlation because erosion rates increased with increasing hardness, contrary to what is expected based on existing theories that use hardness as the single materials parameter to model erosion.     

Thermodynamic studies of Zn-O interactions in dilute liquid copper alloys

The effect of Zn on the activity coefficient of oxygen in liquid copper at low concentrations has been determined using a solid electrolyte galvanic cell: (—) Pt, W/O (Cu-O-Zn), l//ZrO₂-CaO//NiO-Ni/pt (+) The interaction parameter ε _o ^(Zn) is found to be −256 at 1100°C, −203 at 1150°C, and −160 at 1200°C. From the results, the enthalpy and entropy interaction parameters have been evaluated. A comparative study of the solute interactions in Cu-O solutions containing Mn, Fe, Co, Ni, and Zn is made in the light of the solution models.     

Self-propagating high-temperature synthesis of composite targets based on titanium carbonitride,silicide, and aluminide for ion-plasma deposition of multifunctional coatings

The macrokinetic features of combustion of the mixtures in the Ti-Al-Si₃N₄-C system calculated for the formation of compact ceramic materials (CCMs), the composition of which is described by the general formula X(TiAl₃) + (100 − X)(0.448TiC_0.5 + 0.552(Ti₅Si₃ + 4AlN) with mixture parameter X = 10–50%, are investigated. Compact CCM samples with the main structural components in the form of TiC _x N _y grains and binding phases TiAl3 and Ti5Si3 are fabricated by the technology of forced self-propagating high-temperature synthesis (SHS) compaction. An increase in X promotes the formation of the M _n +1AX _n phase with the composition Ti₃SiC₂ in the synthesis products. Complex investigations into the physicomechanical properties of the obtained ceramics are performed. Based on their results, the inverse dependence of the density and hardness of compact materials on parameter X is established. Tests of the samples for oxidation resistance showed that the obtained CCMs based on titanium carbonitride, silicide, and aluminide possess excellent resistance to high-temperature oxidation, and their oxidation rate in air at t = 900°C for 30 h does not exceed 7.8 × 10⁻⁵ g/(m² s).     

Effect of heat treatment on the properties of nanostructured magnetically hard Pr-Dy-Fe-Co-B materials

Effect of heat treatment (HT) in the temperature range from 400 to 1000°C on the properties of sintered (Pr_{1 − x} Dy _x )_{12 − 17}(Fe_{1 − y} Co _y )_balB_{5 − 15} (x = 0−0.73 and y = 0.15−0.87) magnets is studied. It is shown that, depending on the cobalt and boron contents in the material, its composition and the dependence of H _cI on heat treatment conditions change. In the HT temperature range 700–900°C, an H _cI minimum is found: the “depth” of the minimum increases with increasing cobalt content. The minimum of H _cI is reversible; i.e., after HT at 1000°C, the coercive force increases to the value corresponding to the composition of the material whatever the temperature of preliminary HT. A model that explains the dependence of H _cI of the material on the HT conditions by a diffusion redistribution of boron between the basic R ₂F₁₄B (2-14-1 intermetallic) and RF ₂, RF ₄B, RF ₃B₂, and RF ₂B₂ phases (with R = Pr + Dy, F = Fe + Co) is suggested.     

Finely dispersed Si3N4−SiC powders and materials based on them

The objectives of the present research were to investigate the preparation of homogeneous ultrafine composite Si₃N₄−SiC powders by a plasmochemical process and the properties of ceramics produced from them. The chemical and phase compositions of the powders depended on the particle size of the initial powder, silicon input rate, and ratio of ammonium and hydrocarbon flow rates. The particle size and specific surface area of the compounds depended on the concentration of particles in the gas jet, and the cooling rate of the products. Composite powders containing from a few up to 90 mass % SiC, with specific surface areas of 24–80 m²/g and free silicon and carbon content less than 0.5 mass % were obtained. The main phases present were α-Si₃N₄, β-Si₃N₄, β-SiC, and X-ray amorphous Si₃N₄. Dense materials were prepared both by hot pressing at 1800°C under a load of 30 MPa and gas-pressure sintering at 1600–1900°C under a pressure of 0.5 MPa nitrogen. The plasmochemical composites had smaller pore sizes, were finer grained, and densified more rapidly than materials sintered from commercial powders. Institute of Inorganic Chemistry, Latvian Academy of Sciences, Salaspils. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 7–12, January–February, 1999.     

Interaction of silver and phosphorus with zirconium, niobium, and molybdenum

Interaction of components in the systems (Zr, Nb, Mo)−Ag−P is studied by X-ray analysis and phase diagrams are constructed at different temperatures for various phosphorus contents. Ternary compounds are not found in the systems studied. In the Zr−Ag−P system silver dissolves in phosphide Zr₁₄P₉ up to the limiting composition Zr_10.8Ag_3.2P₉. Comparative analysis is performed for interaction of components in (Zr, Nb, Mo)−(Cu, Ag)−P systems. L'vov State University. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 36–39, January–February, 1999.     

The strain dependence of postdynamic recrystallization in 304 H stainless steel

Using double-hit hot compression tests, the softening behavior of 304 H stainless steel was studied during unloading. The prestrains used were associated with the initiation of dynamic recrystallization (DRX) (ε _c), the peak strain (ε _p), 1/2 (ε _c+ε _p), the strain at maximum softening rate (ε _i), and the onset of steady state flow (ε _s). The following conditions of deformation were used: T=1000 °C, 1050 °C, and 1100 °C, =0.01 and 0.1 s⁻¹, and delay times of 0.3 to 1000 seconds. To define the above important strains, single-hit hot compression tests were performed over a wider range of deformation conditions than the double-hit ones—i.e., 900 °C to 1100 °C and =0.01 to 1 s⁻¹. The results show that a transition strain (ε*) separates the strain-dependent range of postdynamic softening from the strain-independent range. At strains between ε _c and ε*, both metadynamic and static recrystallization contribute to interhit softening. The value of ε* obtained in this work was ε*=4/3 ε _p. It was also found that the strain hardening rate was identical at all the critical strains (ε*) and took the value −22 MPa.     

Interaction coefficients in the iron-carbon-titanium and titanium-silver systems

A liquid Fe-C-Ti system was studied by establishing an iso-titanium-activity state for ternary samples at 1600 °C through the medium of a bath of liquid silver which permits diffusion of titanium only. From the two iso-titanium-activity lines obtained, the self-interaction coefficients of titanium and interaction coefficients of carbon on titanium in liquid iron were estimated:ε _Ti ^Ti = 4.67, ρ_Ti ^Ti = 0.32, ε_Ti ^C = −11.94, ρ_Ti ^C = −4.52, ρ_Ti ^Ti,C = −9.96 An experimental study has been made of the distribution of titanium between liquid silver and liquid iron at 1600 °C. By the use of the interaction coefficients of titanium and r_Ti ^o in liquid iron, the thermodynamic parameters of titanium in liquid silver were determined asr _Ti ^o _Ag = 2.44 X 10⁻³, (ε_Ti ^Ti _Ag = −6.17, (ρ_Ti ^Ti)_Ag = −16.3     

Manufacturing porous materials from metalorganic mixtures: Report 2

The morphology of the surface and fracture of highly porous materials obtained during the thermal destruction of metalorganic mixtures (MOM) was investigated. The size and shape of pore channels in the finished product were shown to be determined through the fractional composition and the particle shape in MOMs. The effect of the porosity on the permeability and strength of sintered materials was considered. The permeability was demonstrated to depend not only on the value, but also on the shape of pore channels. Combining the techniques of powder metallurgy with chemical-metallurgical processes allows us to obtain materials with a porosity of 70–80% and a strength of no less than 5–25 MPa. If the pore size was from 10 to 100 μm, the permeability of materials was (in 10⁻¹² m²) 1–3 for Mo, 0.5–6 for Mo-Ni, and 2–6 for Ti-Mo.     

A study of the thermodynamics and phase relationships of the Fe−Co−S−O quaternary system

The oxygen potentials of several three- and two-phase equilibria in the Fe−Co−S−O quaternary system were measured atP _SO2=1, 0.1, and 0.01 atm over wide temperature ranges. The measurements were carried out using a solid oxide electrolyte emf technique. The equilibria measured are sp+ε+δ, s+ε+ξ, sp+ξ+η, and sp+δ. The symbols sp, ε, δ, ξ, and η denote the spinel, monoxide, monosulfide, metal sulfate, and Fe₂O₃ phases, respectively. Compositions for several of the equilibrated phases were measured using electron probe microanalysis. The present results and literature data for the constituent ternary systems were used to obtain thermochemical solution parameters for the sp, ε, δ and ξ solid solution phases. The calculated potential-composition stability diagrams for SO₂ pressures of 1, 0.1, and 0.01 atm at 973, 1023, and 1073 K, respectively, are in good agreement with the experimental results. OMRAN A. MUSBAH, formerly Research Associate at the University of Wisconsin-Madison     

Mixing models for gas stirred metallurgical reactors

The mixing of liquids in ladles, (0.5 ≦L/D ≦ 2.0), agitated by a centrally rising bubble plume, has been analyzed both theoretically and experimentally. An exhaustive review of previous metallurgical literature on mixing in ladles and furnaces demonstrates that the majority of previous investigators in the field consider mixing to be brought about primarily by turbulent diffusion phenomena. The present study clearly shows that mixing is a combination of both convection and eddy diffusion processes, neither of which can be disregarded for gas stirred systems. For predicting mixing times during such gas injection procedures, a simple empirical equation is proposed for axisymmetric systems:τ _mαε_m ^−1/3L⁻¹R^5/3. Hereτ _m is the 95 pct mixing time,ε _m is the specific energy input rate,R is the vessel radius, andL is the depth of liquid. On the basis of physical and mathematical modeling, the rate of liquid mixing in conventional gas injection ladle metallurgy operations is compared with those observed in C.A.S. (composition adjustment by sealed argon bubbling) systems. It was found that mixing in C.A.S. operations is relatively slow and highly insensitive to gas flowrates(i.e., specific energy input rates).     

Enthalpies of formation of borides of iron,cobalt, and nickel by solution calorimetry in liquid copper

The enthalpies of formation at 1385 ±2 K of the following crystalline borides have been determined by high temperature solution calorimetry using liquid copper as the calorimetric solvent. Fe₂B-67.87 ±8.05 kJ mol⁻¹, Co₂B -58.1 ±7.0 kJ mol⁻¹, Ni₂B -67.66 ±4.12 kJ ml⁻¹, FeB-64.63 ±4.34 kJ mol⁻¹, CoB -69.52 ±6.0 kJ mol⁻¹, and NiB -40.2 ±3.77 kJ mol⁻¹. The enthalpy of fusion of NiB has been determined to be 28.25 ±1.54 kJ mol⁻¹ at its melting point of 1315 K. New data are reported also for the enthalpies of solution of iron, cobalt, and nickel in copper, and for the enthalpies of interaction between these metals and boron in dilute solutions in liquid copper.