Vol 60, No 6 (2019)

Some developments by Academician V.N. Antsiferov and his scientific school are considered from the viewpoint of their further development when fabricating structural powder materials and products. The prospects of work for the fabrication of concentration-inhomogeneous and trip steels are noted. There is great potential in the possibility of controlling the thickness and volume of the zone of the deformation martensite transformation occurring during the fracture. It is advisable to continue works on the fabrication of fullerene-containing and nitrogen-containing powder compositions, as well as on studying the structural heredity of powder steels. The possibility of synthesizing fullerene-containing phases during the liquid-phase sintering of “iron–cast iron” and “iron–graphite” compositions and their subsequent redistribution in the material bulk during dynamic hot pressing deserves attention. It is reasonable to fabricate nitrogen-containing steels by the mechanical activation of powders with subsequent sintering in dissociated ammonia not only when forming wear-resistant and corrosion-resistant steels, but also heat-resistant materials. Works on studying the decomposition of supercooled austenite in powder steels of various alloying systems having different process prehistories (sintered, hot-deformed, infiltrated, etc.) are promising. Works on studying hot deformed concentration-inhomogeneous materials fabricated, in particular, based on powders of the Distaloy type, are promising. Original procedures developed by the school of Academician V.N. Antsiferov are valuable. This is, in particular, the procedure of determining the concentration variation coefficient, as well as the magnitometric complex and mathematical model providing the possibility to forecast the decomposition of supercooled austenite. Works by V.N. Antsiferov can be in-demand when solving the problem of lean alloyed powder steels with a lower bainite structure, which provide the optimal combination of strength and viscosity.

Powders of the KhN60M alloy (EP367, 06Kh15N60M1) are investigated. An overview of manufacturing methods of products of the KhN60M alloy is presented with the analysis of their advantages and disadvantages. It is shown that, when compared with the casting technology and hot pressing of powders of high-alloyed special steels and alloys, additive technologies enable fabricating complexly shaped products with a high level of physicomechanical properties and material utilization factor. The low casting properties of the alloy under study are the reason for the research into atomization to meet the requirements for size, shape, morphology, and fluidity of powders for additive technologies. The goal of this work is to study the influence of the argon pressure during gas atomization on the physical, chemical, and process properties of powders for laser surfacing formed from the KhN60M alloy. The gas atomization technology of the liquid melt by argon using a VIGA 2B laboratory atomizer was used to fabricate the metallic powder of the KhN60M brand at 1560°C and varying the atomizing gas pressure in a range of 22–25 mbar. To select the atomization parameters, the values of the melt viscosity are calculated using the ProCast system for the computer simulation of casting processes by the finite element method and the temperature dependence of viscosity is constructed. The shape and size of the particles and their granulometric composition are studied using laser sedimentation and electron and optical microscopy. The quantitative metallography data are processed using the VideoTest 4 software. The fluidity of powders is measured. It is established that the fraction of spherical particles increases and fluidity of powders improves with an increase in the atomizing gas pressure; the Feret diameter, average particle size, and d₅₀ values vary insignificantly. An experimental dependence of an increase in the yield of the target fraction powder (40–60 μm) with a decrease in the atomizing gas supply is found. The inversely proportional dependence of the fraction of spherical particles on the desired cut fraction is established. The results of the study make it possible to predict the output parameters of powders when atomizing KhN60M steel. Characteristics of powders of the fraction –80 + 40 μm with a shape factor of 0.99 and fluidity of 14–15 g/s make it possible to use them for manufacturing products using additive technologies.

The dependence of the phase composition and parameters of a fine structure of titanium silicon carbide in powders formed by the self-propagating high-temperature synthesis on the aluminum concentration in the 5Ti/2Si/1C reaction mixture is investigated. The aluminum content is varied in a range of 0.1–0.4 mole fraction with the conservation of the total carbon content. It is established that the additives of aluminum not only affect the yield of titanium silicon carbide, but also promote the preferential formation of Ti₅Si₃ in synthesis products instead of TiSi₂ identified in powders containing no aluminum. The introduction of a small amount of aluminum (0.1 mole fraction) leads to the formation of the Ti₃Si_{1 – x}Al_xC₂ solid solution and makes it possible to decrease the content of impurity phases in SHS powders by 6%. The silicon carbide concentration in SHS powders decrease at a higher aluminum content in the reaction mixture, while that of binary compounds (TiC, Ti₅Si₃, TiAl) correspondingly increases. No noticeable effect from the introduction of aluminum on the parameters of the crystal lattice of titanium silicon carbide in SHS powders is found in concentration limits of 0.1–0.25 mol %. A noticeable increase in parameters of a and c for Ti₃Si_{1 – x}Al_xC₂ (from a = 3.067 Å, c = 17.67 Å to a = 3.07 Å, c = 17.73 Å) with the conservation of the c/a ratio in limits of known values (c/a = 5.78) is observed only with the aluminum concentration of 0.4 mole fraction. The crystallite size of titanium silicon carbide depends, first and foremost, on the combustion parameters. At the same time, the deformation of the crystal lattice of Ti₃Si_{1 – x}Al_xC₂ in SHS powders increases monotonically with an increase in the aluminum content in the reaction mixture in the concentration range under study.

This mini review is devoted to analysis of the latest advances in the development of aluminum-based composite materials (CMs) reinforced by microstructures and nanostructures. The fabrication methods of CMs, various reinforcing additives (Al₂O₃, AlN, SiC, CuO, B₄C, Li₃N, C, and BN), and their morphological types (nanotubes, nanoplates, microparticles, and nanoparticles), as well as the structure and properties of CMs, are considered. The importance of theoretical modeling methods for studying the strength of interfaces in CMs is shown.

Diffusion and homogenization in “iron (5 μm–nickel (5 μm or 50 nm)” powder systems of various degrees of dispersion during sintering (900 and 1000°C), as well as spark plasma sintering, are investigated using the Matano–Boltzmann method. Calculated diffusivities in pairs of micron powders sintering without applying pressure (900°C, 6 h) and by the spark plasma method (900°C, 5 min) in these systems are equal to 7 × 10^–10 cm²/s. It is shown that the use of nanodispersed nickel powder in diffusion pairs based on finely dispersed iron powder promotes a twofold increase in diffusivity at 900°C in contrast to the pair with the microdispersed nickel powder. Constants in the Ivensen sintering kinetics equation are calculated for the “iron–nickel” powder systems, by which the factors activating sintering of these systems are established. The dependences of the structural phase composition and physicomechanical properties of carbide steels of the Fe(base)–14 wt % Ni–8 wt % TiC system on the sintering temperature in range t = 900–1200°C and structure dispersity and homogeneity are determined. The dependences of the grain size, porosity, hardness, microhardness, fracture toughness, and bending ultimate strength on the sintering temperature are shown. Dependences of tribotechnical properties on the degree of homogeneity of the solid solution and volume of the phase transformation of metastable austenite into deformation martensite during abrasive friction turn out similar for carbide steels and diamond tools based on carbide steel. Optimal values of the variation coefficient of the nickel concentration in austenite and carbide steels of the same chemical composition but with different degrees of dispersity, which provide the maximal volume of the austenite decomposition and high values of the diamond-tool grinding coefficient, turn out equal to 5 in both systems, but the sintering parameters are different. It is shown that the physicomechanical properties of the studied systems depend on the structure porosity and dispersity, while tribotechnical properties depend on the structural homogeneity of steels.

The surface preparation is a prerequisite for ensuring the required properties of a diamond film formed by gas-phase deposition. The influence of the temperature and concentration of the CuSO₄ etchant on the structural and phase compositions of the surface of hard-alloy materials is considered in this work, and the structural and phase compositions of a continuous polycrystalline diamond film at its growth stages is also considered. The adhesion of the diamond films to the surface of hard-alloy materials is determined qualitatively. It is established that the treatment of the hard-alloy surface in the CuSO₄ solution at t = 23°C leads to the inhomogeneous removal of a cobalt binder with chipping WC grains and the formation of the porous structure in the surface layer of the WC–6% Co alloy. The treatment by the CuSO₄ etchant at t = –2°C provides the homogeneous etching of the Co binder over the boundaries of WC grains and the formation of a chemically homogeneous surface. The orientation growth and adhesion of the diamond film depend on the elemental composition of the WC–Co alloy surface after treatment by the CuSO₄ solution. If the treatment was performed at t_sln = 23°C, then the removal of copper from the defect surface WC layer is complicated during the synthesis, which provides the multidirectional growth of diamond crystals in the film along two directions, 〈111〉 and 〈110〉, which causes critical biaxial compressive stresses (2.5 GPa) and leads to low film adhesion to the hard alloy surface. If the treatment is performed at t_sln = –2°C, then the orientational growth of diamond crystals in the film occurs in one preferential crystallographic direction 〈111〉, which lowers the biaxial compressive stresses (1.7 GPa) and increases the adhesive bond of the film to the hard alloy surface. The structure imperfection calculated from the ratio of the lines of integrated intensities I₁₃₃₃/I₁₅₈₀ using the Raman spectroscopy method decreases with an increase in concentration at negative temperatures and increases at positive temperatures of the CuSO₄ solution during surface preparation.

The objects of the investigation are the powder of 12Kh18N10T stainless steel of the 20–63 μm powder and experimental samples formed based on it by selective laser melting (SLM). The powder was fabricated by argon atomization at a temperature of 1640°C and pressure of 27 bar. The particle structure is dendritic–cellular, and the cellular structure prevails with a decrease in the particle size (<35 μm), while the dendritic almost disappears. The characteristic particle size is d₅₀ = 37 μm and d₁₀₀ = 67 μm. The differential distribution is close to the Gaussian form, while asymmetry is associated with the satellite character and the presence of innumerous particles smaller than 20 μm in size. The powder fluidity is 3.27 g/s, while the apparent density is 4.41 g/cm³. The density of the samples of the 12Kh18N10T steel samples grown using a Concept Laser M2 installation under a laser power of 180 W and speed of 700 mm/s is 7.89 g/cm³ on average. Since the density of compact steel is 7.95 g/cm³, the material is rather high-density. The microstructure of the 12Kh18N10T sample is continuous, has no pores and cracks, and comprises the austenite solid solution. The average size of coherent scattering regions in the grain bulk is 19 nm. The arc-shaped interfaces of parallel semicircular tracks are formed due to the crystallization heat removal during the SLM. The elongated crystallites in the tracks are oriented inwards from the arc-shaped interface. The microhardness of the samples in the transverse plane of the metallographic section is higher than the microhardness of the planar plane. Herewith, the microhardness of the samples formed by the SLM method is higher than that of the standard compact alloy. The ultimate strength and relative elongation are 651 MPa and 47%, respectively. An increase in strength is apparently due to refining structural parameters after SLM. The fracture surface of the samples is characteristic of the clearly pronounced viscous type.

Trends and prospects for the development of industry according to materials of European and world congresses on powder metallurgy and publications in leading specialized foreign editions are analyzed. Trends of the stable development of the production of powder structural parts for the automotive industry in developed countries, including using assembly technology during joint sintering, are noted. The production of articles using MIM methods is constantly growing, and micro MIM technology has become a separate subindustry, making it possible to manufacture products 0.1 g and less in weight. HIP methods have found a second use; it becomes possible to fabricate large-scale billets from corrosion-resistant steels up to 1000 kg in weight, and post-HIPing technology is used increasingly to improve the quality of products fabricated by additive technologies and important castings. Products up to 100 kg in weight are already being fabricated using additive technologies. The author’s opinion on the developmental prospects of powder metallurgy in Europe and around the world is also formulated, and the developmental directions of industry in Belarus and its influence on the development of global powder metallurgy are determined. In particular, new brands of economically alloyed powder steels are being developed. They make it possible to decrease the prime cost of mass structural parts without worsening their technical characteristics. For the same purpose, the processes of sintering combined with quenching are improved and endogas is used for cooling instead of nitrogen, unlike foreign analogs.