Powder Metallurgy and Metal Ceramics最新文献

Seven different divalent transition metal sulfates (MgSO₄, CuSO₄, NiSO₄, CoSO₄, FeSO₄ · 7H₂O, ZnSO₄, and MnSO₄) and sodium carbonate (Na₂CO₃) were used as raw materials to synthesize a series of unary (MgCO₃, CoCO₃, ZnCO₃, FeCO₃, and MnCO₃) and quaternary (MgNiZnX)CO₃ (X = Mn, Fe, Co, Cu) carbon high-entropy materials under hydrothermal conditions. Microstructural studies of the obtained quaternary high-entropy carbonates are conducted, aiming to discuss the influence and causes of various transition metals on high-entropy phase formation, laying the experimental foundation for the preparation of high-entropy materials with different combinations of transition metals. Meanwhile, the phase and microscopic morphology of the samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that most quaternary compounds present a pure phase isomorphic with anhydrous carbonate. However, the presence of Cu as a component in the products hindered the formation of pure-phase high-entropy carbonates due to the influence of the Jahn–Teller effect. Additionally, each component's ionic radius and stabilization energy difference are the main reasons for the diffraction peak shift. Furthermore, variations in constituent elements played a crucial role in controlling particle morphology, with Fe favoring the formation of smooth spherical particles. At the same time, Cu exacerbated surface roughness on spherical particles, and the presence of Mn facilitated the formation of aggregates.

The rotor and nozzle blades are critical components of a gas turbine. Their materials and design determine the allowable gas temperature at the turbine inlet and directly influence the technical and economic performances of gas turbine engines. Improving gas turbine cycle parameters requires the development of fundamentally new blade protection systems and transition from oxidation-resistant multicomponent coatings to thermal barrier coatings. The structure and properties of an external zirconium dioxide ceramic coating deposited on a gas turbine blade airfoil using high-speed evaporation–condensation were studied to assess the potential for extending blade service life. X-ray diffraction analysis of yttria-stabilized zirconia showed that the content of the tetragonal and monoclinic phases was 30 wt.% and 50 wt.%, respectively. This indicates incomplete transition (stabilization) of the monoclinic phase into the tetragonal phase during powder synthesis. Hightemperature annealing of the ceramics promotes phase redistribution, which positively influences the powder structure by increasing the tetragonal phase content to 70 wt.%. The ceramic coating was deposited in a vacuum of 1–10^–2 Pa using electron-beam heating of the blades to 870–900°C. Optimal process parameters were established to enable the formation of an external ceramic layer on the blade airfoil with a thickness ranging from 80 to 120 μm. The deposited ceramic coating exhibits a columnar structure, with an average crystallite diameter of 2–3 μm and length approximately equal to the coating thickness. The microhardness of the ceramic coating ranges from 500 to 700 MPa. The findings demonstrate that the external thermal barrier ceramic coating applied to gas turbine blades by high-speed evaporation–condensation ensures a monoclinic (5–10%) to tetragonal (90–95%) phase ratio that corresponds to the most acceptable service properties.

This research explores the sustainable utilization of basalt powder waste from Bali’s ornamental stone industry as an alternative aggregate in mortar production. Through comprehensive material characterization by X-ray fluorescence, X-ray diffraction, and field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy methods (XRF, XRD, and FE-SEM EDS, respectively), we identified that basalt waste contains 81.29% pozzolanic material with anorthite as the dominant phase, indicating excellent potential for construction applications. The study evaluated mortar formulations with varying compositions (75–91% basalt, 9–20% cement, 5% gypsum). The optimal mix of 75% basalt, 20% cement, and 5% gypsum demonstrated superior mechanical properties, reaching a compressive strength of 6.94 MPa compared to 1.31 MPa for raw basalt while maintaining comparable density and water absorption characteristics. Practical application tests confirmed that ornaments produced with this eco-friendly mortar maintained identical visual quality to conventional products. The findings present a viable circular economy solution that simultaneously addresses industrial waste management and supports the preservation of Bali’s traditional craftsmanship. This approach reduces environmental impacts by reusing industrial byproducts and provides economic benefits through value-added material recovery. The incorporation of basalt waste into high-quality building materials demonstrates significant potential for sustainable development in regional craft industries.

Nickel-clad titanium–chromium carbide powders were subjected to high-temperature oxidation in air at 600–1000°C. The effect of nickel content (17, 25, and 33 wt.%) on the oxidation resistance of the powders and their oxidation mechanisms was examined. Plasma spraying of the (Ti, Cr)C–Ni powders into water was also conducted to study oxidation processes during deposition. The oxidation rate was found to rise with temperature, with significantly intensified oxidation upon reaching 800°C. Clad particles of the (Ti, Cr)C–Ni powders with a nickel surface layer in contact with the environment showed higher weight increment during oxidation compared to nonclad (Ti, Cr)C powders. Nickel cladding, depending on temperature, can prevent or slow the oxidation of (Ti, Cr)C particles. With higher nickel content in the powder, the thickness and continuity of the clad layer increased, thereby enhancing oxidation resistance. Analysis of the microstructure and composition of the oxidized powders revealed that multilayer oxide films composed of Ni (NiO) and Ti (TiO₂, Ti_xCr_yO_z) formed on their surface. These films slowed the diffusion of oxygen into the particles but did not stop it completely. At 600–700°C with one-hour holding, the clad Ni coating partially oxidized with the formation of a surface NiO film but did not fail and retained its continuity. The clad layer showed more pronounced degradation and loss of continuity at 800°C. At 900–1000°C, the clad Ni layer underwent intense oxidation and was destroyed. The (Ti, Cr)C particles also significantly oxidized, resulting in the formation of a multilayer oxide film based on Ti and Cr (Ti_xCr_yO_z). This film was predominantly porous and did not prevent the diffusion of oxygen into the particles. During plasma spraying of the powder into water, the particles hardly oxidized and retained the microstructure and chemical composition close to the original ones.

Changes in the structure of clad NPG-75 graphite powder in the application of plasma coatings were examined. The starting NPG-75 powder consisted of 25 wt.% graphite and 75 wt.% nickel. During plasma spraying of the NPG-75 powder, the graphite content in the coatings significantly reduced and did not exceed 4 wt.%. Several factors contributing to the reduced graphite content in the coatings were considered, specifically: effect of high temperature on the integrity of the nickel shell and graphite burnout as the powder passed through the plasma flow, blowing of the nickel shell by the vortex plasma flow and subsequent graphite burnout, nickel delamination upon collision of clad particles with the substrate, and influence of plasma spraying parameters. To assess the effect of high temperatures on the NPG-75 powder structure, the starting powders were oxidized in air at 600–1000°C for 60 min. The influence of plasma flow on the nickel shell integrity was determined by spraying the NPG-75 powder into water, followed by metallographic analysis to evaluate the nickel content. A mechanism for nickel delamination upon collision of NPG-75 powder particles with the substrate was proposed. The influence of plasma spraying parameters on the structure and graphite content of the resulting coatings was studied in detail. The research enabled the identification of methods for retaining graphite content in Ni–C composite coatings.

In this research work, Al–SiC (8 wt.%)–Al₂O₃ (2 wt.%) and Al–SiC (6 wt.%)–Al₂O₃ (4 wt.%) bulk composites were synthesized via mechanical alloying and spark plasma sintering at 550°C and 50 MPa for and 15 min hold. After consolidation, bulk samples did not exhibit any new peaks compared to powder samples, as indicated by XRD patterns. The hardness of the sintered samples was analyzed by a Vickers microhardness tester at 1 N for 20 s hold, and the wear resistance of the samples was studied by fretting wear test at 20 and 30 N loads. The consolidated samples exhibited Vickers microhardness of 1.5 ± 0.5 GPa and 1.4 ± 0.35 GPa for the two compositions sintered for 10 min hold. When the holding time increased to 15 min, the hardness values decreased to 1.35 ± ± 0.45 GPa and 1.34 ± 0.25 GPa, respectively. The wear volume losses were higher at 30 N load compared to 20 N load due to higher deformation and formation of a rough surface in the sample, leading to the sample's breaking. The bulk samples of the two compositions sintered for 10 min hold exhibited compression strengths of 492 and 476 MPa, respectively. The strength decreased to 482 and 467 MPa, respectively, when the sintering time was increased to 15 min. The decrease in hardness and compressive strength values can be attributed to increased grain size at a higher holding time. The fracture surface exhibited ductile and brittle fracture modes in the Al matrix and reinforcement phases.

In this study, the mechanical and electronic properties of W₂CoB₂ hard phases in the WCoB–TiC ceramic composites with varying Cr contents were analyzed using first-principles calculations. Experimental measurement was conducted to determine the microstructure, hardness, transverse rupture strength (TRS), and fracture toughness (K_Ic) of WCoB–TiC ceramic composites with different Cr contents. First-principles calculations showed that adding a small amount of Cr could increase the bulk elastic modulus of the material. However, as the concentration of Cr increased, its bulk elastic modulus decreased. Moreover, it was found that Cr doping effectively enhanced the material's toughness, which might be attributed to strengthening the covalent bond property of the B–Cr chemical bond with higher Cr doping concentrations. The experimental results indicated that Cr doping reduced the density of Cubatic ceramic composites. Still, a small amount of Cr could refine the grain size of the hard phases, thereby enhancing the overall mechanical properties of the composites. The WCoB–TiC ceramic composites achieved the highest hardness, TRS, and K_Ic values of 92.3 HRA, 906.5 MPa, and 12.45 MPa ∙ m^1/2, respectively, at a Cr content of 2.0 wt.%.

It is known that TiC can be formed as a result of solid-phase reactions in SiC–TiO₂–CaO systems. To synthesize TiC-based ceramics or SiC/TiC multiphase ceramics using this reaction, it is first necessary to research the high-temperature physicochemical reactions and phase equilibrium relationships within the reaction system, which will serve as the basis for formulation optimization and process guidance. Therefore, solid-state reactions and phase equilibrium relations in the quinary SiC–SiO₂–TiC–TiO₂–CaO system and its boundary SiC–TiO₂–CaO system at 1400°C were investigated through experiments and thermodynamic calculations. The results suggest that the system undergoes numerous high-temperature physicochemical reactions. First, TiO₂ reacted with SiC to form TiC through a displacement reaction: TiO₂ + SiC = TiC + SiO₂. Then, SiO₂ immediately reacted with CaO, forming calcium silicates such as CaSiO₃, Ca₃Si₂O₇, Ca₂SiO₄, or Ca₃SiO₅. At the same time, excess TiO₂ and CaO react to form calcium titanates, such as CaTiO₃, Ca₃Ti₂O₇, or CaTiSiO₅. Experiments confirmed the equilibrium relations of TiC with salt-like compounds in the oxide SiO₂–TiO₂–CaO system, except for CaTiSiO₅, which was not obtained due to the reduction of TiO₂ in the samples, resulting in the formation of Ca₃Ti₂Si₃O₁₂ and Ti₂O₃. Upon meticulous examination of the phase relationships within the SiC–SiO₂–CaO ternary system, it has been conclusively demonstrated that SiC coexists in equilibrium with all calcium silicate salts. The binary, ternary, and quaternary phase relationships within the system were successfully determined, and based on this, a tentative scheme of phase relationships in the SiC–SiO₂–TiC–TiO₂–CaO system was established. There are seven TiC-containing four-phase regions and six SiC/TiC-containing four-phase regions. These works would benefit compositionally designing MC ceramic and MC/SiC composites.

The effect of key process parameters on the structural features and mechanical properties of the multicomponent creep-resistant 57Nb–10Cr–5Al–21Ti–7Mo (at.%) alloy produced by powder metallurgy methods from a mixture of elemental metal powders was studied. The production process included consolidation of the powder mixtures, part of which underwent mechanical activation in a planetary mill with subsequent hot forging. Some of the hot-forged samples were annealed in a vacuum furnace at 1600°C. The hot-forged materials exhibited a heterogeneous structure, consisting of a solid-solution matrix based on the Nb–Mo system and evenly distributed grains of an intermetallic phase based on the Ti–Al system, and were characterized by pronounced anisotropy. A gradient distribution of Al and Nb within the titanium grains after hot forging was revealed. Annealing at 1600°C altered the grain morphology and resulted in near-complete homogenization of the alloy with the formation of a single-phase bcc structure. The highest mechanical properties at room temperature and 600°C were observed for the materials produced by hot forging of a powder mixture ground for 30–60 min. At 1000°C, the yield stress of the alloy annealed at 1600°C exceeded σ_0.2 of the hot-forged alloys not subjected to annealing and reached the level of the as-cast alloy of the same composition.

This part of the review focuses on wet chemistry methods that do not involve pressure effects on the starting components. The features of synthesizing nanocrystalline powders of both unstabilized ZrO₂ and ZrO₂-based systems are described. Under precipitation, the synthesis completeness and physicochemical properties of the powders depend on the concentration of reagents, pH of the environment, precipitate washing quality, and drying methods. For deagglomeration of powders, high-energy grinding in ball mills, azeotropic distillation in an aliphatic alcohol environment with more than three carbon atoms, ultrahigh-frequency radiation, pulsed magnetic field, and their combinations with ultrasonic treatment in the powder synthesis process are employed. Coprecipitation using microemulsions was developed to produce powders with spherical particle morphology. The sol–gel process relies on polycondensation and hydrolysis processes and is believed to be a simple method to synthesize homogeneous powders of complex composition. The use of microwave heating in the powder sol-gel synthesis process and the influence of synthesis conditions on powder sinterability are shown. The preparation of mesoporous ZrO₂-based materials, which are promising for the development of catalysts for their special structural characteristics, is considered. The Pechini method (citrate method and polymer complex method) is used to synthesize highly homogeneous and superfine oxide materials, employing complexation and intermediate preparation of a polymer gel. The properties of powders produced through various modifications of the Pechini method are compared. The potential for producing nanosheets is shown. Zirconia-based powders synthesized with the discussed methods were used in the development of sorbents and photocatalysts, solid oxide fuel cells, various optical materials, advanced thermal barrier coatings, nanofiltration membranes, nanostructured amorphous composites with high strength, and functional materials for medical applications, particularly for diagnosis and therapy.