Search Results (609)

This work focuses on wire arc additive manufacturing for the rapid prototyping of shell-type parts such as sealed containers/capsules required in the manufacturing of metal components using hot isostatic pressing (HIP) of powder. The selected material was AISI 316L. The automatic generation step of robot trajectories from the CAD design of the part to be manufactured was addressed first. The mechanical and metallurgical properties of WAAM samples were then evaluated. Finally, a hollow cylindrical capsule manufactured by WAAM was used for the HIP sintering of powder to demonstrate the relevance of the hybrid technology. The main results are as follows: 1. The Ultimate Tensile Strength (UTS) of AISI 316L WAAM samples was measured be-19 tween 540 MPa (longitudinal direction) and 600 MPa (transverse direction). 2. The as-manufactured WAAM parts present a residual (δ) ferrite content of 5–7%. 3. HIP processing permitted to reset a fully austenitic structure within the WAAM wall/shell. 4. The grain size was found to be coarser in the WAAM walls and finer in the core of the part (made of sintered powder). Finally, the suggested hybrid process may become an alternative technology for the manufacture of medium-size metal components in the nuclear industry. Full article

This study reports the successful fabrication and application of floatable syntactic foams derived from fine magnesium powder (<45 µm) utilizing expanded perlite (0.25 g/cm³, 0.2–0.4 mm) as the pore former. Sample disks with densities as low as 0.9 g/cm³ were produced via the classical press and sinter process. To ensure reasonable mechanical properties, the specimens were formed under a pressure of 200 MPa in a hardened steel die, followed by high-vacuum sintering (~3 × 10⁻⁶ torr) at 640 °C for 1 h. The resulting foams exhibited sufficient mechanical strength to allow for precision machining into a microboat. We demonstrated their potential use as a Marangoni-induced microswimmer. Spontaneous locomotion was observed when ethanol was used as a propellant, which generates a surface tension gradient between the upper and rear parts of the swimmer. The microboats achieved propulsion speeds of approximately 160 mm/s when propelled by a 95% ethanol + 5% ink mixture. Using a small volume (~4 µL) of the alcohol mixture, the swimmer could cover distances exceeding 350 mm. Full article

The investigation of the behavior of ZrB₂-SiC-based ultra-high temperature ceramic (UHTC) materials under high-velocity CO₂ plasma flow is of significant importance and relevance for evaluating their prospective use in the exploration of planets such as Venus or Mars. Accordingly, the degradation process of a ZrB₂-30 vol.% SiC ceramic composite, fabricated by hot-pressing at 1700 °C with a 15 vol.% Ti₂AlC sintering aid, was examined using a high-frequency induction plasmatron. It was found that the modification of the ceramic’s elemental and phase composition during consolidation, resulting from the interaction between ZrB₂ and Ti₂AlC, leads to the formation of an approximately 400 µm-thick multi-layered oxidation zone following 15 min stepwise thermochemical exposure at surface temperatures reaching up to 1970 °C. This area consists of a lower layer depleted of silicon carbide and an upper layer containing large pores (up to 160–200 µm), where ZrO₂ particles are distributed within a silicate melt. SEM analysis revealed that introduction of more refractory titanium and aluminum oxides into the melt upon oxidation, along with liquation within the melt, prevents the complete removal of this sealing melt from the sample surface. This effect remains even after 8 min exposure at an average temperature of ~1960–1970 °C. Full article

Metal-based electrical contact materials (ECMs) are essential in switching devices and rotating electrical machines, where sliding contacts enable reliable current transmission under motion. These materials must exhibit high conductivity, low friction, and wear resistance to meet industrial demands. However, their reliability is limited by wear, oxidation, arcing, and other failure mechanisms that increase contact resistance and degrade performance. To address these issues, researchers have developed self-lubricating metal matrix composites (MMCs), particularly copper (Cu) and silver (Ag)-based composites reinforced with solid lubricants such as molybdenum disulfide, tungsten disulfide, graphite, carbon nanotubes, graphene, and its derivatives. While Cu and Ag provide excellent conductivity, each has trade-offs in cost, oxidation resistance, and mechanical strength. Strategies for improving reliability involve material optimization, surface treatments, lubrication, contact design modifications, and advanced manufacturing. Although MMCs are widely reviewed, self-lubricating Ag matrix nanocomposites (AgMNCs) for sliding contacts are underexplored. This review highlights recent progress in AgMNCs produced by conventional or modern powder metallurgy techniques, focusing on the role of solid lubricants, testing conditions, and microstructure on tribological performance. Wear mechanisms, research gaps, and future directions are discussed, highlighting pathways toward the development of reliable sliding contacts. Full article

Tungsten is a prime candidate material for the plasma-facing components of fusion reactors, thanks to its high melting point, high temperature strength, good thermal conductivity, high erosion resistance, etc. Yet, it has some limitations, mainly its brittle nature, difficulty of machining, and propensity to recrystallize at elevated temperatures. Among the approaches to the improvement of particular properties are alloying, dispersion strengthening, thermomechanical processing, and modifications to the sintering process. This study explores the possibility of combining fine powder size with ultra-high pressure to achieve significant densification at moderate temperatures during hot pressing. Two powder sizes and a range of temperatures from 1000 to 2000 °C were used, and their effects were observed. The resulting tungsten compacts were characterized for their microstructure, density, and mechanical and thermal properties. The high pressure enabled substantial densification already at relatively low temperatures, thanks to the plastic deformation of the powder particles. A significant degree of sintering, as manifested by the microstructural and property evolution, occurred however only at higher temperatures. The compacts exhibited brittleness, calling for further optimization of the method. Full article

This study investigates the influence of Y₂O₃ content and sintering temperature on the microstructure, phase composition, and physico-mechanical properties of zirconia-based ceramics with Al₂O₃ addition. It was shown that varying the stabilizer content within 3.0–6.0 wt.% Y₂O₃ leads to observable changes in the phase composition and grain size, as well as affecting the density and microhardness of the material. The sintering conditions ensuring the required density and homogeneous microstructure at moderate temperatures were determined. This research is aimed at optimizing synthesis and heat treatment parameters to produce a dense material with minimal porosity and stable mechanical characteristics. The samples were shaped by uniaxial pressing and sintered in the temperature range of 1530–1570 °C. The structure and phase composition were analyzed using X-ray diffraction and scanning electron microscopy, while the physico-mechanical properties were evaluated by measuring apparent density, porosity, and microhardness. The sintering temperature of 1550 °C was identified as optimal for achieving the highest performance characteristics while maintaining structural homogeneity. The addition of Al₂O₃ contributes to a reduction in the sintering temperature without compromising the material’s properties. Full article

Semiconducting clathrates are a distinct class of inclusion compounds with considerable interest for thermoelectric applications. We report here the synthesis, crystal structure and thermoelectric properties of Sn₃₈Sb₈I₈. The compound was synthesized via planetary ball milling of the corresponding elements for 6 h and then sintering of amorphous mixture at 620 K for 3 days. The crystal structure of the polycrystalline product was determined via X-ray powder diffraction and Rietveld refinement as a type-I clathrate (a = 12.0390(2), space group Pm-3n, No. 223) with mixed-occupied Sn/Sb framework sites and fully occupied I guest sites. Further analysis on the chemical composition, nanomorphology and vibrational modes of the material was carried out via Induced-Coupled-Plasma–Mass Spectrometry, SEM/EDX microscopy and Raman spectroscopy, respectively. Thermoelectric measurements were performed on hot-pressed samples with ca. 98% of the crystallographic density. The clathrate compound behaves as an n-type semiconductor with a band gap of 0.737 eV and exhibits a maximum ZT of 0.0016 at 473 K. Theoretical calculations on the formation enthalpy, electron density of states and transport properties provide insights into the experimentally observed physical behavior. Full article

Aiming at the drawbacks of the classic CoCrFeNi high-entropy alloy (HEA)—low room-temperature strength and softening above 600 °C, which fail to meet strict material requirements in high-end fields like aerospace—this study used the vacuum hot-pressing sintering process to prepare CoCrFeNiTa_x HEAs (x = 0, 0.5, 1.0, 1.5, 2.0 atom, designated as H4, Ta_0.5, Ta_1.0, Ta_1.5, Ta_2.0, respectively). This process effectively inhibits Ta segregation (a key issue in casting) and facilitates the presence uniform microstructures with relative density ≥ 96%, while this study systematically investigates a broader Ta content range (x = 0–2.0 atom) to quantify phase–property evolution, differing from prior works focusing on limited Ta content or casting/spark plasma sintering (SPS). Via X-ray diffraction (XRD), scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS), microhardness testing, and room-temperature compression experiments, Ta’s regulatory effect on the alloy’s microstructure and mechanical properties was systematically explored. Results show all alloys have a relative density ≥ 96%, verifying the preparation process’s effectiveness. H4 exhibits a single face-centered cubic (FCC) phase. Ta addition transforms it into a “FCC + hexagonal close-packed (HCP) Laves phase” dual-phase system. Mechanically, the alloy’s inner hardness (reflecting the intrinsic property of the material) increases from 280 HV to 1080 HV, the yield strength from 760 MPa to 1750 MPa, and maximum fracture strength reaches 2280 MPa, while plasticity drops to 12%. Its strengthening mainly comes from the combined action of Ta’s solid-solution strengthening (via lattice distortion hindering dislocation motion) and the Laves phase’s second-phase strengthening (further inhibiting dislocation slip). Full article

Microwave (MW) sintering offers a promising alternative to conventional heating in powder metallurgy, providing faster processing, lower energy consumption, and improved microstructural control. In the diamond tool industry—where cost-efficiency and competitiveness are critical—MW–hybrid sintering shows strong potential for producing segments designed for cutting and polishing natural stone and construction materials. This study investigates the effects of sintering temperature, dwell time, and green density on the densification and mechanical properties of metal matrix composite (MMC) segments containing diamond particles. MW sintering reduced the optimum sintering temperature by 90–170 °C when compared to conventional free sintering. Under optimal conditions (57% green density, 820 °C, 5 min dwell), segments achieved ~95% densification and mechanical properties comparable to hot-pressed (HP) samples. Although MW–hybrid sintered matrices exhibited slightly lower Young’s modulus (~15%) and Vickers hardness (~20%), their flexural strength and fracture toughness remained comparable to HP counterparts. Overall, MW hybrid sintering provides a cost-effective, energy-efficient, and scalable route for fabricating high-performance diamond tool segments, supporting both economic viability and sustainable, competitive manufacturing. Full article

Compared to pure aluminum powder, aluminum alloy powders exhibit higher strength and hardness, which leads to greater difficulty in plastic deformation during cold compaction, consequently impairing green compact formation and subsequent densification. This study introduces pure aluminum powder into the raw material system based on 2024 aluminum alloy powder and SiC powder, effectively improving the powder compaction characteristics. A systematic investigation was conducted to examine the effects of sintering temperature (460–640 °C) and holding time (5–120 min) during pressureless sintering on the sintering shrinkage, relative density, mechanical properties, and microstructure of SiC_p/Al composites reinforced with 35 wt.% of 31.9 μm SiC particles. The results indicate that sintering at 600 °C for 30 min constitutes the optimal process condition, achieving effective interparticle bonding while preventing coarsening of both precipitates and pores. Subsequent hot pressing effectively enhanced the relative density and mechanical properties of the sintered preforms, achieving a maximum tensile strength of 343 MPa, which represents an improvement of over 70% compared to the sintered-only state. For the hot-pressed state, elevated levels of SiC particle content and size compromised its mechanical performance. This work demonstrates a highly operable and industrially viable processing route for manufacturing aluminum matrix composites using alloy powders. Full article

The processing of fine and technogenic chromite-bearing raw materials accumulated in tailings and sludge storage facilities is a key challenge for sustainable metallurgical development. This paper presents the results of laboratory and pilot-scale studies on the application of vibro-briquetting technology for flotation concentrates and waste materials from JSC “TNC Kazchrome” (ERG). For the first time in Kazakhstan, a pilot-scale validation of vibro-briquetting of flotation chromite concentrates was carried out, resulting in pilot confirmation of the vibro-briquetting technology. The optimal technological parameters of the process were established, and the effectiveness of various types of binders was evaluated. Pilot-scale trials demonstrated that the use of organic and mineral binders ensures the production of durable briquettes with a low yield of fines (around 2%). Comparison with conventional agglomeration technologies (pelletizing, sintering, roller-press briquetting, extrusion briquettes) highlighted the advantages of vibro-briquettes in terms of energy efficiency, environmental performance, and suitability for fine raw materials. It was shown that composite binders (lignosulfonate + cement) provide enhanced strength and water resistance in briquettes, as well as optimal conditions for strength development during thermal–moisture treatment. The findings confirm the high potential of vibro-briquetting technology in Kazakhstan as an energy-efficient and environmentally friendly solution for the integrated utilization of local chromite resources. The proposed vibro-briquetting technology makes it possible to process previously unused gravity and flotation tailings of chromite ores from the Kempirsai Massif, thereby improving the comprehensive utilization of mineral resources and reducing environmental impact. This development is of great importance for Kazakhstan’s industry, as it represents the first pilot-scale testing of cold vibro-briquetting technology for flotation concentrates. Full article

Additive manufacturing methods can constitute a valuable alternative to conventional production techniques for components used in the heavy industry, particularly in foundry applications. This innovative manufacturing approach enables an expanded product portfolio as well as higher precision and geometrical complexity of ceramic components. One additive technology applicable to ceramic processing is robocasting, classified within the direct ink writing (DIW) family. In this method, a semi-fluid ceramic paste is extruded to build the part layer by layer; the shaped green body is subsequently fired (sintered) to attain its final functional properties. This study presents the results of materials characterization of printed ceramic filters, encompassing phase composition analysis, density measurements, three-point bending strength testing, hardness, and microstructural examination. The investigations demonstrated that the oxide ceramic Al₂O₃ processed by the modern robocasting method exhibits mechanical performance at a comparably high level relative to classical manufacturing routes (slip casting, ceramic injection molding, dry pressing). Moreover, the porosity results indicate that 3D printing technology enables lower post-sintering porosity. Full article

To address the challenges of regulating micropore properties and improving the tribological performance of porous polyimide (PPI), PPI/PTFE composites were fabricated via cold pressing–sintering. The effects of PTFE content on porosity, oil absorption/retention, and tribological behavior were systematically studied. Results show that PTFE addition significantly reduced porosity—by 1.8% to 7.9% as PTFE increased from 5 wt% to 30 wt%—while markedly enhancing dry friction performance. The friction coefficient decreased from 0.22 to 0.06 with 30 wt% PTFE, with optimal performance at 20 wt% (friction coefficient: 0.068; wear rate: 1.5 × 10⁻⁶ mm³/N·m). Oil-impregnated samples exhibited further improved tribological properties (friction coefficient ≈ 0.047), attributed to lubricant release forming a protective oil film. Although PTFE promotes lubricant release, it increases wear at higher contents. A PTFE content of 0–10% balances porosity control and tribological performance. Full article

This study reports the synthesis, structural characterization, and electromagnetic shielding performance of tantalum (Ta)-doped nickel ferrite (NiFe₂O₄) composites reinforced with chopped strands. Ta-doped NiFe₂O₄ powders were prepared via the conventional mixed-oxide route and sintered at 1200 °C for 4 h, resulting in a well-crystallized single-phase spinel structure. Comprehensive structural and chemical analyses were carried out using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS), confirming the successful incorporation of Ta into the NiFe₂O₄ lattice and the uniform microstructural distribution. The ferrite powders were subsequently embedded with chopped strands and epoxy resin through hot pressing to fabricate composites with varying filler contents. The electromagnetic interference (EMI) shielding effectiveness (SE) of the composites was systematically evaluated in the 7–18 GHz frequency range using a network analyzer (NA). The optimized composite, with a thickness of 1.2 mm, demonstrated a maximum SE of 34.74 dB at 17.4 GHz, primarily attributed to interfacial polarization, dipolar relaxation, and multiple scattering effects induced by the chopped strands. The results indicate that the shielding performance of the composites can be precisely tuned by modifying the filler concentration and microstructural characteristics, enabling selective frequency-band applications. Overall, this work highlights the potential of Ta-doped NiFe₂O₄/chopped strand composites as lightweight, cost-effective, and high-performance candidates for advanced microwave absorption and electromagnetic shielding applications in defense, and next-generation communication technologies. Full article

Porous La₂MoWO₉ (W-LAMOX) impregnated with a eutectic mixture of lithium, sodium, and potassium carbonate (LNKC) ceramic membranes was synthesized and evaluated for carbon dioxide (CO₂) sensing applications. Structural, microstructural, and electrical characterizations were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), and impedance spectroscopy. The results indicate that sintered thinner membranes, prepared by the tape casting method, exhibit faster and more reproducible responses to CO₂ exposure than sintered thick pressed pellets. These findings highlight the potential of these composite membranes for application in CO₂ sensing technologies. Full article