Powder Metallurgy and Metal Ceramics最新文献

Since 1994, the Ukrainian Phase Diagrams and Thermodynamics Commission has been a part of the Alloy Phase Diagram International Commission (APDIC), in which 18 representatives from 26 countries of the world participate in its activities. The exchange of scientific information and coordination of activities of the international scientific community, mainly in the field of phase diagrams and thermodynamics, promoting the application of phase diagrams in industry and fundamental science, and dissemination of the methodology of critical evaluation of scientific information in world science are among the priority tasks of the APDIC’s activity. As part of the annual report of the Ukrainian Commission, at the APDIC meeting on June 30, 2023, information was presented on the results of the activities of Ukrainian scientists in this field in 2022. It is presented in the form of a table with data on the studied systems and obtained results and a list of references to published papers. Scientists from the Frantsevich Institute for Problems of Materials Science (National Academy of Sciences of Ukraine, Kyiv), Taras Shevchenko National University of Kyiv (Ministry of Education and Science of Ukraine, Kyiv), and Donbas State Engineering Academy (Ministry of Education and Science of Ukraine, Kramatorsk) provided relevant information to the Ukrainian Commission.

The 316L stainless steel meets all health, strength, and quality standards and is an irreplaceable material in the manufacture of medical equipment. The study focused on the 316L austenitic stainless steel, manufactured with the conventional technique in accordance with ASTM A276/A276M–17 Condition A (samples rolled and annealed at 1050°C with water cooling) and with the selective laser melting (SLM) technique (as-printed starting samples). Unlike conventional manufacturing techniques, SLM offers significantly greater design freedom. An AxioMat 200M optical microscope was employed to analyze the microstructure in different lighting modes, and Kalling’s and Marble’s reagents were used to reveal the structure. The 316L steel produced conventionally mainly consisted of austenite (microhardness of 239 kg/mm²), and substantial cross- sectional grain heterogeneity was established in the test sample. Twins and an atypical multidirectionally oriented dense acicular structure in the area of individual grains (microhardness of 260‒286 kg/mm²) and a unidirectional loose structure (microhardness of 317‒328 kg/mm²) were observed. The microstructure of the 316L steel produced with the SLM technique mainly consisted of austenite (microhardness of 268 kg/mm²). The boundaries of the primary austenite grains were revealed with Marble’s reagent, and arc-shaped structures of the melt bath were established. Kalling’s reagent revealed an atypical multidirectionally oriented intragranular substructure, located primarily between the tops of next-layer tracks in areas where previous-layer tracks overlapped (longitudinal microhardness of 239–251 kg/mm² and cross-sectional microhardness of 286–317 kg/mm²). Elongated columnar grains were found using differential interference contrast microscopy. The average ultimate strength of the steel samples produced with the conventional technique was higher than that of the samples produced with SLM by 4.63%, yield strength by 1.53%, relative elongation by 8.27%, and relative contraction by 18.36%. The lower level of properties and greater spread of their values for the SLM steel were due to the presence of elongated grains and anisotropy relative to the buildup direction. The actual level of properties shown by the SLM steel in the starting state meets the regulatory requirements.

As component manufacturing technology evolves, more demands are placed on improved performance of metal/alloy powders in medical, military, machining, and 3D printing applications. High-quality powders are characterized by low oxygen content, precise alloy composition, small particle size, and high particle sphericity. Coupled gas atomization powder preparation technology is an ideal choice for preparing high-quality powders with high atomization efficiency, low oxygen content, and high cooling rate. However, this powder preparation technology’s multiphase flow and multiscale coupling is a complicated physical process. In addition, the mechanism of atomization has not yet been fully understood. Thus, there is no consensus on the atomization phenomena and atomization mechanisms. Close-coupled gas atomization powder preparation technology is facing great challenges in the field of low-cost mass production of high-quality powders. Therefore, it is expected to improve the close-coupled gas atomized powder preparation technology and achieve breakthroughs in atomization principle, such as high-efficiency gas atomization technology, intelligent control of the high-efficiency gas atomization process, and so on. In this respect, this review summarizes the atomizer structures, gas atomization flow field-testing technologies, and gas atomization flow field numerical simulations based on relevant literature. In addition, the gas atomization mechanism of the closely coupled atomizers will be analyzed. Finally, several research directions are proposed for further in-depth studies on the atomization characteristics and mechanisms of close-coupled vortex loop slit atomizers.

The isoperibolic calorimetry method was employed to determine, for the first time, the partial and integral mixing enthalpies for melts in the Eu–Ge system over the entire composition range at 1200 K and 1370–1440 K. The minimum mixing enthalpy for these melts was –49.1 ± 4.4 kJ/mol and was shown by the alloy with x_Ge = 0.45, while (Delta {overline{H} }_{{text{Eu}}}^{infty }) = –145.7 ± 22.3 kJ/mol and (Delta {overline{H} }_{{text{Ge}}}^{infty }) = –166.8 ± ± 19.8 kJ/mol at 1400 ± 3 K, correlating with the solid-state behavior of these melts. This allows categorizing these melts within the series of the Ge–Ln (lanthanide) systems and justifying the thermodynamic properties of melts in the Eu–Ge system, in particular, and in the Ge–Ln system, in general. Using the thermochemical properties for melts in the Eu–Ge system, the ideal associated solution model was employed to optimize and calculate the Gibbs energies, enthalpies, and entropies of formation for the melts, associates in melts, and intermetallics. A large number of associates, especially EuGe, formed in the studied melts because of the highest probability of collision between two dissimilar atoms in liquid alloys. The maximum mole fraction of the EuGe associate reached 0.48 and those of Eu₃Ge, Eu₂Ge, EuGe₂, and EuGe₃ were 0.2, 0.26, 0.24, and 0.26, respectively. The activities of components in melts of the Eu–Ge system showed substantial negative deviations from the ideal solution, correlating with our thermochemical properties. This all indicated strong interactions between dissimilar atoms in melts of the Eu–Ge system, likely involving the transfer of valence electrons of europium to the 4p orbital of germanium. The ΔG values over the entire composition range were greater than ΔH, with ΔG_min = –28.8 kJ/mol at x_Ge = 0.45. Moreover, the ΔG function was also almost symmetrical because of the entropy contribution (mixing entropy of the studied melts was negative, and ΔS_min = –15.0 J/mol K at x_Ge = 0.45). The calculations based on the ideal associated solution model also established that the (Delta {overline{H} }_{{text{Eu}}}^{infty }) values for melts in the Eu–Ge system increased insignificantly with temperature, while (Delta {overline{H} }_{{text{Ge}}}^{infty }) increased more substantially. This might be due to the break of covalent bonds between germanium atoms. Complete information on the thermodynamic properties of all phases was obtained, enabling a thermodynamic description of the Eu–Ge system for the first time.

Additive manufacturing is a process of producing parts, involving incremental addition of material onto a flat or axial substrate. This manufacturing option is also called ‘growth’ because the product is formed by continuously building up layers of material until it is complete. Additive materials and techniques are modern and relevant. Employing these techniques, materials can be produced with various types of energy to fuse powders. The structurization mechanism is virtually unknown in this case. Using additive manufacturing techniques, samples were prepared from the VT1-0 alloy powder on a VT20 alloy substrate and from the VT20 alloy powder on a VT1-0 alloy substrate. The structures of samples cut out from different areas of the deposited material were studied and their microhardness was measured. The relationship between the structure and microhardness in the deposited material was shown. A structurization mechanism for titanium material through the deposition of titanium powder was proposed. A mechanism for the formation of pores in the metal was suggested. The structurization process was characterized by the redistribution of doping elements in the deposited metal and the substrate, as evidenced by changes in microhardness. The microhardness varied from the level characteristic of the substrate metal to the microhardness inherent in the deposited metal. The temperature gradient during the growth of a metal sample was uneven. This led to changes in the size of the structural components in the metal. The powder was fused layer by layer, with the formation of pores depending on the powder particle size. Larger particles formed larger pores compared to those formed by finer powders. The processes established in the experiments were consistent for both deposition options. The difference resided in the base metal, specifically its chemical composition. The proposed mechanism enhanced the general understanding of the structurization processes during additive growth (deposition) of titanium alloys from their powders.

This study investigates the machining of FLC-4608 (designation by Metal Powder Industries Federation, standard 35) sinter-hardened steel compacts with 90% relative density during turning operation. The objective of the study is to analyze the effect of cutting velocity and feed rate on the cutting force component in the direction of cutting motion using chip characteristics. The results showed that the combination of high cutting velocity and low feed rate is the appropriate condition to obtain a low value of the cutting force component. The results also indicated that the machining configurations considered produce shear-localized segmented chips, also known as saw tooth chips, and that the chip formation process involves almost complete densification of the uncut chip material. Except for chip length, all the investigated chip characteristics, minimum and maximum chip thickness, shear band microstructure, and structure below the tip of the chip segment were consistent with the results of the cutting force component. As the feed rate increased, the minimum and maximum chip thickness increased, which was consistent with the increasing value of the cutting force component. Similarly, through the microstructure of the adiabatic shear band and the structure below the tip of the chip segment, increasing cutting velocity showed the dominance of the thermal softening effect over strain hardening and strain rate hardening, consistent with the decreasing value of the cutting force component. This approach is novel, as chip characteristics have received little attention in previous studies on the machining of PM materials. The present study is potentially helpful to the PM industry in achieving better machining process control through a thorough understanding of the results related to the cutting force component in the direction of the cutting motion. The future scope discussed in this report also has prospects for advancing the science of machining PM materials.

The introduction of high-entropy alloys, notable for their increased hardness and thermal stability, gave impetus to the study of their properties in coatings. High-entropy metal coatings are characterized by high hardness, ranging from 7 to 19 GPa. The general laws governing the influence of various parameters on the mechanical properties of high-entropy metal coatings were analyzed. Single-layer metal, nitride, oxide, and carbide coatings and multilayer nitride coatings from high-entropy alloys produced by different deposition techniques were examined. The phase composition, structure, hardness, elastic modulus, and friction coefficient of the coatings were determined. The mechanical properties of high-entropy coatings, along with those of cast alloys, depend on the lattice parameter. With increase in the lattice parameter in bcc metal coatings, the elastic modulus and hardness decrease. The increased hardness of vacuum high-entropy coatings contributes to decrease in their friction coefficient compared to the cast state. The influence of pressure in the sputtering chamber and the voltage applied to the substrate on properties of the nitride coatings was established. The capabilities of producing thick (up to 80 μm) coatings combining metal and nitride interlayers from high-entropy alloys and determining their properties were shown. For the high-entropy carbide in the TiZrNbVTaHf system, the influence of the lattice parameter on hardness was revealed. The lowest friction coefficient (0.05) was observed in high-entropy oxide coatings. The high-entropy coatings showed high hardness. A hardness level of 19 GPa was reached for a metal coating based on the TiZrNbTaHfCr alloy, 63 GPa for a nitride coating based on the TiZrNbVHf alloy, and 48 GPa for a carbide coating based on the TiZrNbVHfTa alloy. The analysis showed that nitride coatings were the hardest, while the lowest friction coefficient was possessed by oxide coatings.

Features peculiar to the synthesis of SiC–Si₃N₄–Si₂N₂O composite powder with a controlled content of silicon carbide, nitride, and oxynitride phases, as well as the structure and properties of hot-pressed ceramics produced from this powder, were examined. The optimal composition of the synthesized SiC–Si₃N₄–Si₂N₂O powder was achieved by heating a 1 : 3 mixture of thermally expanded graphite (TEG) and silicon up to 1200°C in air. The interaction of TEG with fine silicon at 1200°C led to the formation of a solid solution of carbon in silicon carbide, accompanied by heat release. The generated heat increased temperature within localized volumes of the TEG cellular structure to a level where air nitrogen facilitated the development of silicon nitride and oxynitride and an amorphous phase. The amorphous phase crystallized as the interaction time increased to 2.5 h. The duration of the process influenced the final distribution of the phases, formed with the participation of CO, SiO, and air nitrogen. The microstructure of the synthesized powder was characterized by a general agglomerated state, resulting from rod and plate forms of Si₃N₄ and Si₂N₂O. Hot pressing of the synthesized SiC–Si₃N₄–Si₂N₂O composite powder with Al₂O₃ and Y₂O₃ activators yielded superfine ceramics, possessing enhanced hardness and fracture toughness (HV10 = 20.7 GPa and K_Ic = 6.5 MPa · m^1/2). The structure of the ceramics sintered at 2000°C differed from those sintered at 1850°C, primarily by higher density and average grain size. The superfine state significantly influenced the abrasive wear resistance of the ceramics in dry friction conditions. The linear wear index of a sample with an average size of structural elements varying from 0.2 to 1.5 μm was 111 μm/km at a sliding speed of 1 m/sec under a load of 0.2 MPa. This was significantly lower than the linear wear index of industrial ceramics of reaction-sintered silicon carbide (RSSC), which was 232.4 μm/km.

Rotary furnaces are used as reactors to intensify chemical processes between the powder and gas atmosphere around it. The furnace rotation leads to relative motion and dilation of the powder layers, facilitating gas access. The paper is devoted to the modeling of nickel oxide powder behavior in a rotary furnace to estimate the contribution of furnace rotation speed to gas permeability when the nickel oxide granules are reduced in a hydrogen atmosphere. Discrete element modeling of powder granules in a rotary furnace was conducted employing Altair EDEM commercial software to estimate the powder gas permeability at different stages. The powder bed in a horizontal cylindrical rotary furnace was modeled as a packing of identical spherical granules with diameters equal to those of the nickel oxide granules. The furnace rotation led to periodic oscillations of the powder along the furnace wall with an amplitude that gradually diminished to some steady value. Gas permeability of the powder bed was evaluated through the porosity function, derived from the Carman permeability equations. Greater gas permeability resulting from significant powder dilation was observed only in active shear zones on the powder bed surface and in the contact area between the powder and the furnace wall. Sizes of the shear zones depended on the furnace rotation speed but never exceeded several granule diameters for all rotation speeds. The efficiency of a rotary furnace as a chemical reactor was shown to be determined not only by the powder dilation but also by the regeneration rate for the powder bed surface. The regeneration rate can be calculated and changes nonlinearly with the furnace rotation speed.