The paper presents a review of existing methods to produce silumins. The possibility of obtaining foundry alloys using amorphous microsilica is shown. Different methods of adding SiO₂ particles into molten aluminum are studied: in the form of aluminum powder — SiO₂ master alloy tablets, particle mixing in the melt at the liquidus temperature and introducing SiO₂ together with a stream of argon. The paper provides calculations of Gibbs energy formation and change enthalpy for silicon reduction by aluminum from its oxide. Calculations demonstrated the thermodynamic possibility of silumin production using amorphous microsilica. The effect of alloying additives and impurities on the silicon reduction behavior is determined. It is found that magnesium can be used as a surface-active additive to remove oxygen from dispersed particle surfaces and reduce silicon from its oxide. It is determined that the method of aluminum-silicon alloy production by introducing amorphous microsilica preheated to 300 °С into the aluminum melt (t = = 900 °С) together with argon stream (with subsequent intensive mixing) features higher efficiency since it ensures producing aluminum-silicon alloys containing more than 6 wt.% of silicon and microstructure of pre-eutectic foundry silumins. Industrial application of the proposed method will improve the efficiency of the existing silumin production process due to savings on purchasing commercial crystalline silicon. Moreover, this technology will minimize the environmental impact by reducing the volume and subsequent eliminating sludge fields used as landfills for storing dust from silicon gas treatment systems containing up to 95 wt.% of amorphous microsilica.

The study covers the dependence of spongy titanium-based powder material porosity on the stress state coefficient during plastic deformation with the prevailing effect of all-round compression. Based on the results obtained in previous papers, an assemblage of yield curves with varying porosity is constructed on the σ —T plane. The yielding condition of the powder material is based on the Modified Drucker—Prager Cap model. The graph of geometrical interpretation of the accepted yielding condition contains straight lines corresponding to different values of the stress state coefficient k = σ/T where о is the average hydrostatic stress, and T is the shear stress intensity. In order to formulate the relationship of porosity (θ, %), average normal stress (σ) expressed in the nondimensional form, and the stress state coefficient (k), intersection points of the yield curve assemblage corresponding to yield surface generatrices on the o—T plane and radial straight lines were used. As a result, an equation of the θ = θ(σ, k) form was obtained. The experimental part of the study was performed in order to test the adequacy of this ratio. Powder blanks pre-compacted at a pressure of 1000 MPa and a temperature of 325 °C were subjected to electrical discharge sawing along the axial section to obtain flat samples (templates). Several characteristic areas were selected on the surface of templates to determine local surface porosity using quantitative metallography. The stress-strain state in representative areas was additionally determined by numerical simulation. The calculated values of the volumetric plastic strain, shear stress intensity and average normal stress were determined in axial section zones corresponding to the studied areas. It is shown that the stress state coefficient varying within a sufficiently wide range (k = —10...—0.86) does not affect significantly the porosity value.

A factor exerting a decisive influence on the complex of mechanical, technological and operational properties when making castings of magnesium alloys with a wide crystallization range is the casting structure. It is impossible to obtain a required structure of Mg— Al—Zn alloys without melt modification in the melting process. The paper provides the results obtained when studying the process of ML5 magnesium alloy modification with various substances. The influence of 0,4—0,45 wt.% magnesite introduced in the melt at a temperature of 720—740 °C was studied, as well as the influence of melt purging with oxygen-free carboniferous gases at the same temperature on the structure of the obtained alloy and the time of modification effect retention. The latter is especially important in large-lot and mass production of small Mg—Al—Zn—Mn alloy castings for a long time when melt pouring into molds takes considerable time. It is shown that oxygen-free carboniferous gases used for ML5 alloy modification ensure mechanical properties of castings 15 — 20 % higher than the standard level according to GOST 2856-79. The efficiency of retaining the effect of modification using the standard method (magnesite) and with oxygen-free carboniferous gases is compared. It is shown that the effect of modification with magnesite remains within no more than 30—40 minutes, while the effect of modification with oxygen-free carboniferous gas remains not less than 4 hours that enables long pouring of alloy into molds.

High-temperature (t = 800 °С) ion nitriding of T15K6 indexable carbide inserts was carried out with regard to the structure formation, phase composition, surface coating thickness ensuring an increase in their durability during the cutting test. It was found that hardness and microhardness values increase to 15 % after ion nitriding, however, with a temperature increase of more than 600 °C they gradually decrease to their initial values. Flexural strength after ion nitriding increases by 27 %. The fractography of fractures in the T15K6 carbide surface layers after ion nitriding for 1 and 2 hours at different temperatures showed a very branched fracture structure on edges with a fragile pattern inside the material. The analysis of T15K6 carbide surface layer microstructures after ion nitriding showed that as the ion nitriding temperature increases, the size of conglomerate carbides in the surface layer decreases. The depth of the T15K6 nitrided layer is 1 to 7 pm. Certain regularities of the effect of various ion nitriding time and temperature conditions on the performance characteristics of products made of TK group titanium-tungsten alloys are determined. At 600, 700, 800 °C ion nitriding temperatures and 1 to 8 hours isothermal exposure time, the increase in hardness, microhardness and tensile strength with lower wear was found when cutting T15K6 indexable carbide inserts. It is determined that as the ion nitriding time increases, intergranular destruction areas expand, while the intragranular areas shrink. In case of ion nitriding, a solid solution (Ti_xW_x)(C_{1_y}N_y) and (Co_{1_x}W_x)(C_{1_y}N_y) supersaturated with tungsten is formed and three and four component compounds are released in the surface layer.

The study covers the microstructure and mechanical properties in submicrovolumes of LS59-1A lead brass. Scanning electron microscopy (EDS) was used for metallographic analysis of the studied sample microstructures. It was found that the LS 59-1A brass microstructure along with the main phases (α phase — solid solution of alloying elements in copper and β phase — solid solution based on the CuZn electronic compound) also contains globular inclusions of free lead (1—2 vol.%) localized on grain boundaries and in interdendritic regions. In addition, exogenous nonmetallic inclusions of CuO + ZnO and pores were found in the microstructure. Oxide inclusions and compounds containing iron and manganese are localized at the boundaries of α and β phases. A nanoindentation method was used to study hardness (Н) and Young’ modulus of α and β phases. An insignificant difference was found between H values for a phase dendrites with respect to the β phase interdendritic space indicating higher homogeneity of LS59-1A ingot mechanical properties. Calculation of additional pressure that occurs at the interface of a and β phases when external force is applied to the material due to a difference in Young’s moduli showed that it is 23 times higher than external force, which can cause destruction of LS59-1A brass ingots during machining. The results obtained are discussed from the standpoint of modern ideas about the metallographic method used to control brass ingot quality under industrial production conditions.

The paper studies the microstructure and microhardness evolution of the Al—0,05vol.%nAl₂O₃nanocomposite (where nAl₂O₃ are alumina nanoparticles) and aluminum without nanoparticles fabricated by accumulative roll bonding as a result of annealing at 373— 573 K. Ball-shaped Al₂O₃ nanoparticles (average diameter of 50 nm) were introduced between the rolled sheets of commercially pure aluminium during the first to fourth rolling cycles to obtain the nanocomposite. The fifth to tenth rolling cycles were carried out without nanoparticles. The average size and aspect ratio of elements with grain-subgrain structures in the as-processed state and after annealing at 473 K were measured using transmission electron microscopy. It is shown that the nanocomposite microhardness is 50—13 % higher than the respective HV value for aluminum at all studied annealing temperatures. The main factor of the higher nanocomposite microhardness is dispersed hardening by Al₂O₃ nanoparticles. The contribution of substructure and grain boundary hardening is the same for both materials. The thermal stability of nanocomposite microhardness is only ~25 K higher than that of aluminum due to the heterogeneous distribution of nanoparticles in the matrix and their small volume fraction. An additional factor is an inherently high thermal stability of an ultrafine-grained structure formed by accumulative roll bonding with respect to other methods of severe plastic deformation. It was found that most of Al₂O₃ nanoparticles remain at nanocomposite grain boundaries after annealing at 473 K, so Al₂O₃ nanoparticles can fix the boundary up to at least 473 K under the studied conditions.

Computational analysis in the Thermo-Calc program (including construction of liquidus surfaces and polythermal sections of the Al—Ca—Ni—La—Fe system) and experimental analysis of the microstructure (by scanning electron microscopy (SEM)) were used to specify the concentration region of the primary crystallization of the aluminum solid solution (Al). This region can be considered promising for the preparation of new in-situ aluminum-matrix eutectic composites containing over 20 vol.% intermetallics in the structure. An analysis of the promising Al—4Ca—2Ni—1La—0,6Fe (wt.%) composition microstructure revealed that it contains up to 23 vol.% (by calculation) Al₄Ca and Al₉FeNi eutectic intermetallic phases with individual crystals of eutectics having sub-micron sizes: length of about 250—400 nm and thickness of 100—200 nm. It was also found that the Al₄La intermetallic phase predicted by thermodynamic calculations is not formed, and La completely dissolves in the calcium-containing Al₄Ca phase. The microstructure and hardness analysis during the staged annealing showed that the simultaneous alloying of the Al—4Ca—2Ni—1La—0,6Fe alloy with zirconium and scandium (0,2 wt.% Zr and 0,1 wt.% Sc) leads to precipitation hardening due to the decomposition of (Al) solid solution and further formation of L1₂— Al₃(Zr, Sc) phase coherent nanoparticles up to 20 nm in size. The analysis of mechanical properties obtained in uniaxial tensile tests of Al—4Ca—2Ni—1La—0,6Fe—0,2Zr—0,1Sc cylindrical castings showed a relatively high level of strength properties (σ_t = 265 MPa, σ_0,2 = 177 MPa), while maintaining an elongation acceptable for the composite (~2 %). Thus, the obtained data demonstrates the possibility ofAl—Ca—Ni—La—Fe system applicability for preparing new in-situ aluminum-matrix composites.

The structure and properties of coarse-grained WC-6%Co hard metals with carbon deficiency from 0,11 to 1,31 % obtained from narrow fraction tungsten carbide powder with a grain size of 5 to 15 pm were studied with respect to the stoichiometric ratio. According to the results of metallographic analysis, 1390 to 1420 °C sintering temperatures provide a non-porous alloy state with normal carbon content, while alloys with lower carbon content feature considerable porosity. It is found that hard metals with less than 0,02 % residual porosity can be obtained at sintering temperatures of 1450-1475 °С regardless of the carbon content. It is shown that alloys with 0,11—0,91 % carbon deficiency have a two-phase structure, while the alloy with 1,31 % carbon deficiency contains n phase inclusions in addition to WC and γ phase. It is determined that lower carbon content slows down the tungsten carbide grain growth process during liquid-phase sintering. EDX analysis was used to determine the concentration of tungsten dissolved in the binder phase — 10, 12, 15 and 19 wt.% for hard metals with normal, low, medium and high carbon deficiency, respectively. Narrow fraction WC powders allow obtaining hard metals with rounded grains having a form factor of about 0,77. The alloy with 0,91 % carbon deficiency with respect to the stoichiometric ratio had the best combination of hardness and toughness (11,1 GPa and 16,0 MPa-m^1/2).