Hardness and electrical resistivity of Al–13 wt % Mg<Subscript>2</Subscript>Si pseudoeutectic alloy

In the present work, effect of growth rates on microhardness, electrical properties and microstructure for directionally solidified Al–13 wt % Mg₂Si pseudoeutectic alloy at a constant temperature gradient were studied. Directional solidification process were carried out with five different growth rates (V = 8.33–175.0 μm/s) at a constant temperature gradient (G = 6.68 K/mm) by using a Bridgman type directional solidification furnace. Microstructure of directionally solidified Al–13 wt % Mg₂Si pseudoeutectic alloy was observed as Mg₂Si coral-like structure phase dispersed into primary α-Al phase matrix. The electrical resistivity for Al–13 wt % Mg₂Si pseudoeutectic alloy, were measured by the d.c. four-point probe method. The dependency ofmicrohardness and electrical resistivity on growth rates were obtained as HV = 135.7 (V)^0.09 and ρ = 17.30 × 10^?8(V)^0.08, respectively for Al–Mg₂Si pseudoeutectic alloy. The results obtained in present work were compared with the previous similar experimental results.     

Effect of scandium on the phase composition and hardening of casting aluminum alloys of the Al–Ca–Si system

The phase composition of the Al–Ca–Si–Sc system is investigated in aluminum corner uisng computational (Thermo-Calc) and experimental (optical microscopy, scanning electron microscopy, and electron probe microanalysis) methods. The influence of annealing on the structure and hardness of alloys containing 0.3 wt % Sc is investigated in the region up to 550°C. It is shown that the maximum in the hardening curve caused by the isolation of nanoparticles of the Al₃Sc (L1₂) is attained after annealing at temperatures of 300–350°C in alloys belonging to the phase region (Al) + Al₄Ca + Al₂Si₂Ca ((Al) is the aluminum-based solid solution). Scandium completely enters the (Al) composition in alloys of this region, while the silicon concentration is minimal in it. On the other hand, hardening is almost absent in alloys from the (Al) + (Si) + Al₂Si₂Ca phase region. The possibility in principle to form the casting alloys based on the (Al) + Al₄Ca + Al₂Si₂Ca eutectic hardened without quenching is substantiated.     

Effect of modification on the solidification of Al–Si aluminum alloys

The solidification of the AK12 alloy processed by a standard flux and a combined modifying flux, which significantly increases the mechanical properties of the alloy at a significant increase in the modifying effect time, is studied. The experimental results are simulated using the ProCAST software package.     

Investigation into the solubility of nanopowders of the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–CeO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system in the aqueous medium at various pH

Nanopowders of ZrO₂–Y₂O₃–CeO₂ and ZrO₂–Y₂O₃–CeO₂–Al₂O₃ systems are investigated with the purpose of studying the influence of pH of the dispersed medium on the solubility of nanopowder particles of a complex composition in an aqueous medium after membrane filtration and centrifugation to further prepare the stable dispersions necessary for toxicological investigations of nanoparticles. Concentrations of elements remaining in a supernatant after the sample preparation, which includes membrane filtration and centrifugation, are measured by inductively coupled plasma optical emission spectroscopy. It is established that that the largest aggregative stability of the nanopowder dispersion without the Al₂O₃ additive corresponds to the optimal range of pH 5.5–9.5, while with the Al₂O₃ additive, it is region pH 7.0. The results evidence that, when dispersing these powders, the hydrosol of yttrium oxyhydroxide, which is dissolved at pH < 6.0, is formed. When dissolving in water of the powder with the Al₂O₃ additive in the neutral medium, aluminum hydroxide is formed; in the acidic medium (pH < 6), it is replaced by main soluble aluminum salts; and in the alkali medium (pH > 7), amphoteric aluminum hydroxide is dissolved because of the formation of aluminates.     

Synthesis and Characterization of Al–Al/(SiO<Subscript>2</Subscript>)<Subscript>np</Subscript> Composite by Powder-in-Tube Method

In this study, a macro-nanocomposite of Al–Al/(SiO₂)_np was synthesized using powder-in-tube method. Pure aluminum cylinders were cast and then machined to prepare tubes. Nanocomposite powders of Al/(SiO₂)_np were prepared by mixing 1 and 2 wt% SiO₂ nano-particle with aluminum. Then macro-nanocomposites were prepared by compaction of the nanocomposites inside the tubes. The effects of reinforcement weight fraction, volume fraction of nanocomposite in the macro-nanocomposites and hot extrusion on the microstructure and mechanical properties were investigated. Scanning electron microscope (SEM) and optical microscope (OM) were used for microstructural examinations. Mechanical properties were investigated using tensile and compression tests at room temperature. The results revealed that when 25 vol% of the powder-in-tube composite was the nanocomposite reinforced with 2 wt% of nano-particle, the tensile strength was increased by 10.8%. Tensile strength was improved by up to 24% when 64 vol% of nanocomposite reinforced with 1 wt% of nano-particle was employed. Additionally, significant increase in compressive strength was achieved. This is noteworthy that coupling of a pure aluminum sheath with the nanocomposite enhanced the strength with limited loss of ductility. Micrographs showed integrated composites in which the interface between the sheath and the core had no defects.     

Thermodynamic Modeling of Metal Desulfurization with Boron-Containing Slags of the CaO–SiO<Subscript>2</Subscript>–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> System

In thermodynamic modeling of the desulfurization of steel by CaO–SiO₂–MgO–Al₂O₃–B₂O₃ slag on the basis of HSC 6.12 Chemistry software (Outokumpu), the influence of the temperature (1500–1700°C), the slag basicity (2–5), and the B₂O₃ content (1–4%)1 on the desulfurization is analyzed. It is found that the sulfur content is reduced with increase in the temperature from 1500 to 1700°C, within the given range of slag basicity. At 1600°C, the sulfur content in the metal is 0.0052% for slag of basicity 2; at 1650°C, by contrast, its content is 0.0048%. Increase in slag basicity from 2 to 5 improves the desulfurization, which increases from 80.7 to 98.7% at 1600°C. If the B₂O₃ content in the slag rises, desulfurization is impaired. At 1600°C, the sulfur content in the metal may be reduced to 0.0052 and 0.0098% when using slag of basicity 2 with 1 and 4% B₂O₃, respectively; in the same conditions but with slag of basicity 5, the corresponding values are 0.00036 and 0.00088%, respectively. Note that desulfurization is better for slag without B₂O₃. According to thermodynamic modeling, metal with 0.0039 and 0.00019% S is obtained at 1600°C when using slag of basicity 2 and 5, respectively, that contains no B₂O₃. The results obtained by thermodynamic modeling for the desulfurization of metal by CaO–SiO₂–MgO–Al₂O₃–B₂O₃ slag of basicity 2–5 in the range 1500–1700°C are consistent with experimental data and may be used in improving the desulfurization of steel by slag that contains boron.     

Investigation into physicomechanical properties and structure of the Al–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite material fabricated using mechanical treatment of the PAP-2 aluminum powder and reaction sintering of powder billets

Mechanical treatment of the PAP-2 powder for 15–180 min results in its granulation and an increase in bulk weight γ_f = 0.4–1.0 g/cm³ in a state of free pouring and γ_s after shaking. Several components of Al differing by the lattice parameter (a₀ = 0.40474–0.40636 nm) have been registered, which is a consequence of structural distortion due to the shocking effect of hard-alloy grinding bodies. The θ-Al₂O₃ crystalline phase is determined (2%). Physicomechanical properties of the Al–Al₂O₃ cermet obtained by reaction sintering in the filtration combustion mode of pressings fabricated from the PAP-2 granulated powder are as follows: density is 2.3–2.5 g/cm³; bending strength is 170–250 MPa; density under the axial and diametral compression is (4.3–7.0) × 10³ J/m², respectively; and relative deformation before destruction under the axial and diametral compression is 6.6–10.8 and 6.2–7.5%, respectively.     

Stabilization of the fluorite phase in the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The calculated and experimental vertical ZrO₂–Y₂O₃ sections of the Zr–Y–O system are compared to find the region of a stable fluorite structure of yttrium-stabilized zirconia (YSZ). X-ray diffraction (XRD) and Raman scattering are used to study the crystal and local structures of mixed oxide 0.82ZrO₂ · 0.18Y₂O₃ (18YSZ) powders prepared by isothermal annealing of a precursor precipitated from a salt solution. The formation of a fluorite-type fcc structure (space group \(Fm\overline 3 m\)) in the powders is detected by XRD. Raman scattering study of the local structure of the cubic 18YSZ powders revealed traces of the tetragonal phase in them.     

Effects of the Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Content on the Viscosity of CaO-SiO<Subscript>2</Subscript>-10 Pct Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Quaternary Slag

The present study experimentally investigates the effect of Cr₂O₃ on the viscosity of molten slags. The viscosities of CaO-SiO₂-10 pct Al₂O₃-Cr₂O₃ quaternary slags with two different binary basicities (R, basic slag with R = 1.2 and acidic slag with R = 0.8) were measured by the rotating cylindrical method from 1813 K to 1953 K (1540 °C to 1680 °C). The results showed that the viscosity of both types of slag decreased as the Cr₂O₃ content increased, but the viscosity of acidic slags exhibited a greater decrease. The slags showed good Newtonian behavior at such high temperatures. Cr₂O₃ could act as a network modifier to simplify the Si-O-Si tetrahedral structure, as verified by the Raman spectral analysis, which was consistent with the decreasing trend of viscosity. The activation energy of viscous flow decreased slightly with increasing Cr₂O₃, but increasing the basicity seemed to be more effective in decreasing the viscosity than adding Cr₂O₃.     

Synthesis of new metal-matrix Al–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–graphene composite materials

The mechanism of formation of ceramic microparticles (alumina) and graphene in a molten aluminum matrix is studied as a function of the morphology and type of precursor particles, the temperature, and the gas atmosphere. The influence of the composition of an aluminum composite material (as a function of the concentration and size of reinforcing particles) on its mechanical and corrosion properties, melting temperature, and thermal conductivity is investigated. Hybrid metallic Al–Al₂O₃–graphene composite materials with up to 10 wt % alumina microparticles and 0.2 wt % graphene films, which are uniformly distributed over the metal volume and are fully wetted with aluminum, are synthesized during the chemical interaction of a salt solution containing yttria and boron carbide with molten aluminum in air. Simultaneous introduction of alumina and graphene into an aluminum matrix makes it possible to produce hybrid metallic composite materials having a unique combination of the following properties: their thermal conductivity is higher than that of aluminum, their hardness and strength are increased by two times, their relative elongation during tension is increased threefold, and their corrosion resistance is higher than that of initial aluminum by a factor of 2.5–4. We are the first to synthesize an in situ hybrid Al–Al₂O₃–graphene composite material having a unique combination of some characteristics. This material can be recommended as a promising material for a wide circle of electrical applications, including ultrathin wires, and as a structural material for the aerospace industry, the car industry, and the shipbuilding industry.     

Obtaining nanopowder pseudo-ligatures Cu–(SiC+Si<Subscript>3</Subscript>N<Subscript>4</Subscript>) for modification and reinforcement of aluminum alloys

The mechanical mixing and subsequent compaction of a powder mixture consisting of carrier powder (electrolytic copper (Cu) with particle size of 20–100 μm) with nanopowder modifier compound (powders of silicon carbide (SiC)—50–70%, silicon nitride (Si₃N₄)—20–30%, sodium hexafluoroaluminate (Na₃AlF₆)—10–20%) with particle size of 70–100 nm obtained by azide technology of self-propagating high-temperature synthesis (SHS) were investigated. The mixtures containing 2.5, 5, 10, 15% of the modifier were investigated. Mechanical mixing was carried out for 30–45 min at speed of 150 rpm in a Pulverizette-5 planetary mill. An analysis of mixing of the raw powder components was performed. Some physicotechnological properties of the obtained powder mixtures, such as particle size distribution, density, bulk weight, and flowability, are determined. The formation of briquettes—the nanopowder pseudo-ligatures from powder mixtures of composition Cu–(SiC + Si₃N₄) with different concentration of modifier—was carried out by cold pressing. Compacting of the received mixtures of powders was carried out in cylindrical mold using a PSU-50 hydraulic press under pressure of 85–310 MPa. The dependence of the relative density and porosity of the briquettes on the pressure of pressing is determined. The microstructures of pseudo-ligatures pressed at maximum pressure of pressing are presented. Briquettes—nanopowder pseudo-ligatures with diameter of 25 mm, height up to 2 mm, weight of 5 g, with relative density of 53–85% and porosity of 15–47%—intended for subsequent input to aluminum melt with the aim of inoculation are obtained.     

Synergistic effect of FeS and ZnS content on the separation of lead and antimony for PbS–Sb<Subscript>2</Subscript>S<Subscript>3</Subscript>–ZnS–FeS quaternary system under water vapor atmosphere

Synergistic effect of FeS and ZnS content on the separation of lead and antimony for PbS–Sb₂S₃–ZnS–FeS quaternary system under water vapor atmosphere has been studed in this paper. The results indicate that FeS can and ZnS can inhibit the volatilization of PbS. Inhibition effect of FeS is superior to that of ZnS to the volatilization of PbS. As to Sb₂S₃, FeS can inhibite the volatilization of Sb₂S₃, but ZnS can promote the volatilization of Sb₂S₃. Inhibition effect of FeS is superior to that of ZnS to the volatilization of Sb₂S₃.     

Influence of alloying the TiC<Subscript>0.5</Subscript>N<Subscript>0.5</Subscript> carbonitride with zirconium on an interaction mechanism with the Ni–Mo melt

The influence of alloying the TiC_0.5N_0.5 titanium carbonitride with zirconium on the mechanism and kinetic features of the contact interaction with the Ni–25%Mo melt (t = 1450°C, rarefaction 5 × 10^–2 Pa) is investigated for the first time by electron probe microanalysis and scanning electron microscopy. The main effects of the modifying influence of zirconium on the dissolution, phase formation, and structure formation processes which occur during the interaction of the Ti_1–n Zr _n C_0.5N_0.5 carbonitride (n = 0.05 and 0.20) with the Ni–Mo melt are revealed and the factors promoting their manifestation are analyzed. The practical absence of zirconium and nitrogen in the composition of the K-phase (the Ti_{1 – n} Mo _n C _x metastable solid solution, where n ≤ 0.65 and x = 0.7 ± 0.1) is confirmed experimentally. It is shown that the zirconiumenriched Ti_0.80Zr_0.20C_0.5N_0.5 carbonitride cannot be recommended as a refractory component of cermet because of the limitations of the chemical character.