Smyrnova-Zamkova, M. YuDudnik, O., VBykov, O., IRuban, O. K....
12页
查看更多>>摘要：Ultrafine 90AZK, 80AZK, 70AZK, and 58.5AZK powders in the Al2O3-ZrO2-Y2O3-CeO2 system were produced for the first time by a combined method involving hydrothermal synthesis followed by mechanical mixing with alpha-Al2O3 (HTSM). The properties of the powders heat treated in the range 400-1450 degrees C were examined by differential thermal analysis, X-ray diffraction, electron microscopy, and nitrogen thermal adsorption-desorption (BET). The sizes of primary particles were calculated with the Scherrer equation. The AMIC (Automatic Microstructure Analyzer) software was applied to process the powder morphology analysis results. The F-ZrO2 -> T-ZrO2 phase transformation was found to proceed completely when the powders were mechanically mixed in the HTSM process. The M-ZrO2 phase was identified as traces in the ultrafine 90AZK and 80AZK powders after mechanical mixing, was not found in the 70AZK powder, and emerged as traces in the 58.5AZK powder above 1150 degrees C. Heat treatment was shown to induce a topochemical memory effect in the ceramics: the morphology and shape factor of the ultrafine powders following heat treatment at 400-1450 degrees C varied topologically continuously. The dependence of primary particle sizes and specific surface area of the powders on the heat treatment temperature indicated that they had high sintering activity. The powders are needed to produce highly efficient ZTA composites in the Al2O3-ZrO2-Y2O3-CeO2 system, consisting of fine particles of the viscous zirconia-based solid solution, codoped with ceria and yttria, distributed in a rigid alumina matrix.
查看更多>>摘要：This research presents a new design of plasma atomization conducted using a graphite plasma conduit to assure prolonged interaction between molten metal and hot plasma jets. The conduit plasma atomization technique implies using a heat-collecting duct to minimize the transfer of heat energy from the plasma arc into the surrounding environment. The interaction between the molten metal and plasma arc jet is more extended. Therefore, the surface tension force of molten metal may be sufficient to form completely spherical particles, thereby eliminating satellites. The scanning electron microscopy (SEM) shows powder particles without satellites after conduit plasma atomization. This research has a strategic role in getting fundamental data for improving the efficiency of the conduit plasma atomization. A statistically designed experimental approach was followed to study the current and pressure parameter variations during newly designed conduit plasma atomization for determining median particle size distribution (D-10, D-50, and D-90). Spherical Ti-based alloy metal powder without satellites was successfully fabricated by conduit plasma atomization with an electric current of 40 and 45 A and at gas pressures of 1.5 and 2.5 bar, using a constant feed of 2 mm(3)/sec. The results showed that optimization is the best parameter for the minimum particle size distribution in metal powders. After optimization, the minimum values resulting from particle size distribution D-10, D-50, and D-90 are 71, 325, and 534 mu m. The required value can be achieved by combining the current and pressure parameters of 45 A and 2.5 bar, accordingly. The regression equation can be used as a reference for operating conduit plasma atomization to obtain the required particle size distribution.
Zakiev, V., IZgalat-Lozynskyy, O. B.Derevianko, O., V
10页
查看更多>>摘要：3D printing of porous SiO2-Al2O3-Fe2O3-MgO-CaO-Na2O glass products with use of the robocasting technique was comprehensively studied. Features in the preparation of glass-based pastes with gelatin or agar for 3D printing were established and recommendations on the printing of porous glass products employing a ZMORPH 3D printer equipped with a thick paste extruder were developed. The method of preparing glass/gelatin and glass/agar pastes for 3D printing was tested experimentally. Mixtures with different contents of gelatin or agar, glass, and water were analyzed, and conditions for their storage from the time the paste components were mixed to the time they were loaded into the 3D printer were determined. The optimal 3D printing parameters were chosen with the Voxelizer software for the ZMORPH 3D printer with a thick paste extruder. A modification to the ceramic module for printing with pastes was proposed. The heat treatment process at 160 and 260 degrees C and sintering at 600-650 degrees C for the printed samples were studied. The temperature threshold at which a powdered glass material sintered without transiting to the molten state was found experimentally by choosing optimal temperatures and holding times. Heat treatment resulted in glass samples of complex shape. The samples reached 49% porosity. The mechanical properties and microstructure of the sintered porous glass samples were analyzed. The wear resistance and fracture of the samples were examined by repeated scratching with a conical diamond indenter.
查看更多>>摘要：Al-Si alloy powder was prepared by the gas atomization method, followed by the production of the Al-50 wt.% Si alloy used in electronic packaging by spark plasma sintering (SPS) under different parameters. Afterward, the alloy's microstructure, phase composition, mechanical properties, coefficient of thermal expansion (CTE), and thermal conductivity (TC) were analyzed. The results show that the uniform Al-50 wt.% Si alloy with a primary silicon size of less than 10 mu m can be obtained by gas atomization and SPS techniques. Compared with the powder, the XRD alloy patterns remain the same after SPS, with alpha-Al and beta-Si diffraction peaks and no other phase formation. The change of SPS temperature and time may affect the accumulation of primary silicon in the alloy and thus influence the alloy's mechanical and thermal properties. The tensile strength of the alloy gradually increased to 220 MPa (550 degrees C, 15 min) with the rise of SPS temperature. In contrast, the coefficient of thermal expansion (and thermal conductivity of the alloy decreased with a further increase in the temperature. Optimal values of coefficient of thermal expansion (10.6 x x 10(-6) K-1), thermal conductivity (128 W center dot m(-1) center dot K-1), and tensile strength (210 MPa) were obtained at 500 degrees C and 15 min of the SPS process. A relationship between the primary silicon morphology and material properties was established to understand the alloy's thermal behavior changes. This change is mainly caused by the CTE and TC values difference between the Al matrix and Si-phase. The initially uniformly distributed primary silicon accumulates and modifies the properties of the alloy. The coefficient of thermal expansion and thermal conductivity variation were discussed in terms of changes in alloy particle morphology, and the theoretical model of CTE was then analyzed.
Prikhna, T. O.Ilnytska, G. D.Loginova, O. B.Tkach, V. M....
9页
查看更多>>摘要：Improvement in the efficiency of diamond tools is inextricably linked with the use of high-strength heat-resistant diamond grains for tooling. Hence, study of the effect exerted by heat treatment on changes in the mechanical characteristics of diamonds produced in various growth systems is a relevant task. The effect of heat treatment (in an inert atmosphere) of diamond powders produced in growth systems using ferroalloys to dissolve carbon and promote the conversion of graphite into diamond on the mechanical characteristics of diamonds and elemental composition of inclusions formed on the crystal surfaces during heat treatment is examined. Following heat treatment in the range 700-1100 degrees C, inclusions are observed on the crystal surfaces in diamonds produced in the Fe-Co-C and Fe-Ni-C growth systems. In our opinion, the effect results from ejection of the liquid metal phase to the surface by capillary forces. In crystals with a higher content of inclusions, the phenomenon of capillary ejection is manifested at lower temperatures than the melting of carbon solvent alloys in the diamond growth process. This is confirmed by a sharp change in the specific magnetic susceptibility shown by the samples with a high content of intracrystalline inclusions in the temperature range 400-800 degrees C. For diamonds with a high content of intracrystalline inclusions, with increase in the heat treatment temperature in the range 700-1100 degrees C, the precipitation of the solvent alloy on the surface of diamond crystals leads to crack generation and decreases the strength of diamond crystals. For diamond samples with a low content of inclusions, when the heat treatment temperature increases to 800 degrees C, the specific magnetic susceptibility and strength hardly change (taking into account the relative error of the data obtained).
查看更多>>摘要：In the present work, Cu-3.0 vol.% WC powders and WC reinforced copper matrix composites were successfully fabricated by combining molecular level mixing (MLM) and spark plasma sintering (SPS) techniques. The microstructure and phase analysis of WC/Cu composite powders prepared by MLM showed that these powders existed in the form of a core-shell structure. Specifically, copper was distributed outside the WC particles as the shell, and WC was located in the center as the core, which initiated the pre-dispersion of WC particles in copper. Furthermore, the thickness of the copper layer was about 10 nm. According to SEM and TEM analysis, the outline of WC/Cu composite particles was closer to a spherical shape. The microstructure characterization of WC-Cu composites showed a good dispersion of the nanoscale WC particles in the composites. Compared to untreated WC-Cu composites, the tensile strength and softening temperature of MLM composite increased significantly from 203 to 223 MPa, and 700 to 800 degrees C, respectively. The density and electrical conductivity of MLM WC/Cu composites increased from 94.18 and 83.2% IACS to 96.72 and 87.5% IACS, respectively. The rise from 17.1 to 20.2% was observed in elongation, as well as tensile strength and toughness by 9.6 and 18.1%, respectively. The above strengthening phenomena were caused by the well-dispersion of WC and Cu phases in the composites. Finally, the wear resistance of composites was tested and contrasted. The results demonstrated that WC particles with uniform distribution decreased composite's COF. The specific COF value of MLM composites was 0.34 and 0.43 for composites without MLM. These results show that uniformly WC particles could effectively enhance the wear resistance of composites. The three-dimensional profile analysis of wear marks also demonstrated that the wear rate of composites was reduced with uniformly distributed WC additives.
查看更多>>摘要：The interaction in the Ni-Ti-B and Ni-Ti-B-Cr systems along the Ni-TiB2 and (Ni-20% Cr)-TiB2 sections was studied. Solid-phase interaction was not found to occur for Ni-TiB2 up to 1200 degrees C. In the case of (Ni-20% Cr)-TiB2, a new phase was formed, Cr2B, with a thickness of similar to 5 mu m at a temperature of 1200 degrees C. The contact melting began above 1200 degrees C in the Ni-TiB2 system and above 1180 degrees C in the (Ni-20% Cr)-TiB2 system. In the (Ni-20% Cr)-TiB2 system, the emerged liquid wetted titanium diboride with an angle of 50 degrees; when temperature increased to 1450 degrees C, the liquid spread completely on the TiB2 surface. In the contact melting process, several areas formed: titanium diboride area, Ni3B and TiB area, Ni and TiB area, and pure nickel. The systems were eutectic and their quasibinary phase diagrams had a eutectic at similar to 9% TiB2 with a melting point of similar to 1200 degrees C at the Ni-TiB2 section and a melting point of similar to 1180 degrees C at the (Ni-20% Cr)-TiB2 section. The alloys in the hypoeutectic part of the phase diagram consisted of the Ni, Ni3B, and TiB phases and additionally of the Cr2B phase in the (Ni-20% Cr)-TiB2 system. In the hypereutectic part of the phase diagram, the metal component disappeared and unreacted TiB2 additionally appeared in the (Ni-20% Cr)-TiB2 system. Zero solid-phase interaction and contact melting observed at temperatures of 1200 and 1180 degrees C, which were significantly lower than the melting points of the interacting components (Ni, Ni-Cr), promoted favorable conditions for the use of nickel as a metal component in wear-resistant composites produced from granular titanium diboride, capable of operating under dynamic and shock loads at elevated temperatures (similar to 900 degrees C) and in corrosive environments.
Zgalat-Lozynskyy, O. B.Ieremenko, L. I.Tkachenko, I., VGrinkevich, K. E....
11页
查看更多>>摘要：The production of ZrN-Si3N4 and ZrN-Si3N4-TiN composites by spark plasma sintering and the mechanical and tribological properties of the consolidated materials were studied. The densification of the ZrN-Si3N4-TiN composites was found to proceed more intensively in the range 1100-1300 degrees C, and nanocrystalline titanium nitride was the main factor that promoted the densification of these composites. Ceramic 57 wt.% ZrN-43 wt.% Si3N4 and 84 wt.% ZrN-16 wt.% Si3N4 samples with a relative density of 0.95 and 0.93 and (84 wt.% ZrN-16 wt.% Si3N4)-15 wt.% TiN and (57 wt.% ZrN- 43 wt.% Si3N4)-30 wt.% TiN composites with a relative density of similar to 0.98 were produced. Microstructural studies showed that components of the consolidated ZrN-Si3N4 composites were uniformly distributed over the material with an average grain size of 200-300 nm. The ZrN-Si3N4- TiN composites had a finer structure, TiN grains being smaller than 100 nm. The mechanical properties of the titanium nitride composites were higher than those of the ZrN-Si3N4 materials. Thus, the Vickers hardness and indentation-determined fracture toughness of the composites containing 15 and 30 wt.% TiN were 18.7 +/- 1.1 GPa and 5.2 MPa . m(1/2) and 19.1 +/- 1.9 GPa and 5.8 MPa . m(1/2), respectively. The hardness of the ZrN-Si3N4 composites was similar to 17 GPa. The tribological properties of the composites were tested with the VK6 hardmetal and silicon nitride. The wear resistance of the ceramic samples directly depended on the contents of zirconium nitride and counterface, i.e., on their physicochemical interaction. When the ZrN content increased to 84%, the tribological properties of the composites improved substantially through the lubricating capability of zirconium nitride. The (84 wt.% ZrN-16 wt.% Si3N4)-15 wt.% TiN composite showed the best tribological properties and can be recommended for use in friction units under dynamic loads.
查看更多>>摘要：SiC/SiC ceramic matrix composite parts have begun to be used in the hot section of gas turbine engines. It is essential to prevent atmospheric corrosion in these parts. Therefore, the development of coating materials with superior properties is of particular scientific interest. The thermal conductivity of coating ceramics is also essential for protecting parts in adverse high-temperature service conditions. In this study, ytterbium silicate-based (YbSi) ceramics used as the top layer in environmental barrier coating were produced by traditional powder metallurgy methods. In addition, they were doped with the rare earth elements Sm and Gd to improve some of their properties. The ceramic samples were structurally characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The thermal conductivity of rare earth elements-silicate samples was measured by the laser flash method. The characterization of samples allowed determining two phases in the rare earth elements-silicate pellets: mono- and disilicate. As a result of Gd doping, the percentage of the disilicate phase increased in the structure. Doping with Sm reduced the amount of this phase. The thermal diffusivity and heat capacity of YbSi ceramic were decreased by doping with Sm and Gd rare earth elements. Consequently, thermal conductivity was significantly reduced by doping Gd and Sm to YbSi ceramics. The thermal conductivity of undoped YbSi ceramics was calculated as 1.98 W(m . K)(-1). However, the thermal conductivity values of YbSi ceramics doped with Gd and Sm amounted to 1.38 and 1.01 W(m . K)(-1), respectively. As a result of Sm doping, the thermal conductivity of YbSi ceramic was reduced by 50%. Thus, RE-doped YbSi ceramics can be a promising candidate for environmental barrier coating applications.
Turchanin, M. A.Dreval, L. O.Agraval, P. G.Korsun, V. A....
9页
查看更多>>摘要：The mixing enthalpies of glass-forming Fe-Ni-Ti, Fe-Ni-Zr, and Fe-Ni-Hf liquid alloys were investigated at 1873 K by high-temperature calorimetry. The thermodynamic properties of melts in the Fe-Ni-Hf system were studied for the first time. Along the studied sections (x(Fe)/x(Ni) = 0.50/0.50 at x(Ti) = 0-0.15, x(Fe)/x(Ni) = 0.50/0.50 at x(Zr) = 0-0.45, x(Fe)/x(Ni) = 0.75/0.25 at x(Hf) = 0-0.18, x(Fe)/x(Ni) = 0.50/0.50 at x(Hf) = 0-0.45, and x(Fe)/x(Ni) = 0.25/0.75 at x(Hf) = 0-0.46), the partial mixing enthalpies of IVB metals and the integral mixing enthalpy showed negative values. New experimental data on the integral mixing enthalpy of the liquid alloys were combined with the literature data, and the increment H-m isotherms of the ternary Fe-Ni-Ti, Fe-Ni-Zr, and Fe-Ni-Hf liquid alloys at 1873 K were plotted using the Redlich-Kister-Muggianu equation. The increment H-m function was negative in each of the studied systems, being indicative of strong interparticle interaction of the components in the glass-forming liquid alloys. The composition dependence of the integral mixing enthalpy of the liquid alloys and its change in the series of the systems can be qualitatively interpreted in terms of the electronegativity of the chemical elements in the liquid alloys.
NSTL
Springer Nature