Sintering Of Powders Research Articles

Boiling performance enhancement and self-recovery of nucleate boiling regime on micro- and nanostructured porous surfaces

In this paper, we report the pool boiling experimental results for significant enhancements in the boiling heat transfer coefficient (BHTC) and CHF on various microporous surfaces. The microporous surfaces were fabricated by metal (Copper) powder sintering process, and nanostructured porous surfaces were additionally fabricated through the thermal oxidation of the metal porous surfaces. Among the examined substrates, a boiling surface with a thin metal porous layer and millimeter-sized porous pillar structures exhibited optimal boiling performance; the BHTC and CHF of the microporous surface were measured to be approximately 500 % and 270 % higher than those of a smooth reference surface, respectively. We conjecture that the results come from the combined effect of active nucleation site density enhancement, capillary wicking promotion, and separation of liquid-vapor flow paths on the microporous surface with porous pillars. On the other hands, the porous pillar surface with needle-like nanostructures showed the interesting phenomena that can be regarded to the recovery of the boiling regime from transition boiling to nucleate boiling. At the CHF, the temperature increase on the surface was slower than that on the other surfaces. Additionally, at high heat fluxes below the CHF, the overheated surface self-recovered to the nucleate boiling state, indicating the rewetting of local dry spots. We consider that the capillary wicking capability strongly improved by the nanostructures on the surface was presumably responsible for inhibiting the irreversible expansion of local dry spots. From the experimental observations throughout this study, we propose the following key requirements to design an ideal boiling surface: increasing the nucleation site density, ensuring a liquid supply path by capillary wicking, separating the liquid and vapor flow paths, and improving the liquid wettability of the solid surface by forming nanostructures.

Biological Applications of Ore Materials: Chili Absorption of Natural MG and ZN Ions Released from Modified Serpentinite Powders

Introduction: This study investigated the characteristics of the powder, the concentration of the ions, and the growth characteristics of Chili that were irrigated with the natural magnesium– zinc ionised water. The findings revealed that the ion dissolution rate was higher for greater water temperatures. Methods: Extended sintering of the zinc-modified natural serpentinite powder at 400°C reduced the number of dissolved magnesium ions and increased the number of dissolved zinc ions. The Chili planting experiment was performed with two groups: 1) Chili irrigated with natural magnesium– zinc ionised water (natural magnesium–zinc Chili) and 2) Chili irrigated with distilled water (distilled-water Chili). Results: The natural magnesium–zinc Chilis were discovered to have higher concentrations of magnesium and zinc ions in various parts. Furthermore, during the later stages of growth, the natural magnesium–zinc Chili had a larger body and did not easily turn yellow, resulting in better freshness. This study used modified serpentine powder to cultivate natural magnesium–zinc Chili. Appropriate powder roasting conditions and the rates of magnesium and zinc dissolution were established, and the growth characteristics of natural magnesium–zinc Chili were determined. Conclusion: The Chilis can help humans ensure healthy lives and promote well-being for all at all ages by sufficient zinc and magnesium intake.

A concept for functional bioceramics with embedded metallization using cold sintering

We demonstrate a novel concept for fabricating bioceramic multilayers with embedded metallization at low temperatures. Using direct cold sintering, i.e., high-pressure consolidation at 1000 MPa and 50°C without transient phase or added binder, we produced gelatine-including hydroxyapatite (HAP) ceramics (70 wt% HAP) with embedded gold (Au) structures. The proposed method eliminates the need for thermal treatment or debinding steps, commonly required for multilayered ceramics with embedded metallization. Obtained ceramic-metal interfaces show good integrity with no delamination when loose ceramic powders consolidated with metallization. The integrity of the interface is attributed to increased roughness between two phases. Our work demonstrates the feasibility of producing multilayered functional bioceramics with embedded circuitry through direct cold sintering of HAP-gelatin powders with Au structures.

Capillary infiltration measurements by finite size drop method: wetting, spreading and infiltration of liquid silver in porous iron

The study proposes a direct method for studying capillary infiltration of porous media using high-speed measurements of the shape of an imbibited droplet of finite size. The method assumes isotropic infiltration, and the change in the droplet volume on the surface is equated to the volume of imbibited liquid. The shape of the imbibited volume in the case of a droplet of finite volume is assumed to be a flattened spheroid. In the mathematical model, the rate of change of the apparent volume obtained in the experiment is reduced to the rate of movement of the liquid front in the porous media.Measurements of capillary processes in the silver (melt)-iron (porous or dense solid) system were carried out at various temperatures in a vacuum of 10-3Pa to verify the model. Time dependencies of the wetting contact angle and the contact diameter of pure silver melt on the surface of dense solid iron, the imbibition rate of silver melt into porous iron, and the kinetics of sintering of iron powder were measured. All measurements were conducted using direct methods of high-speed video and thermal imaging. As a result, in addition to the application of the proposed imbibition model, kinetic dependencies of the mentioned processes at various temperatures in the range from 1000 to 1150 °C were obtained and their activation energies were determined.

Multiple Preheating Processes for Suppressing Liquefaction Cracks in IN738LC Superalloy Fabricated by Electron Beam Powder Bed Fusion (EB-PBF).

In additive manufacturing, controlling hot cracking in non-weldable nickel-based superalloys poses a significant challenge for forming complex components. This study introduces a multiple preheating process for the forming surface in electron beam powder bed fusion (EB-PBF), employing a dual-band infrared surface temperature measurement technique instead of the conventional base plate thermocouple method. This new approach reduces the temperature drop during forming, decreasing surface cooling by 28.6% compared to traditional methods. Additionally, the precipitation of carbides and borides is reduced by 38.5% and 80.1%, respectively, lowering the sensitivity to liquefaction cracking. This technique enables crack-free forming at a lower powder bed preheating temperature (1000 °C), thereby improving the powder recycling rate by minimizing powder sintering. Microstructural analysis confirms that this method reduces low-melting eutectic formation and alleviates liquefaction cracking at high-angle grain boundaries caused by thermal cycling. Consequently, crack-free IN738 specimens with high-temperature durability were successfully achieved, providing a promising approach for the EB-PBF fabrication of crack-resistant IN738 components.

Synthesis and spark plasma sintering of Ti5Si3-Mo powders with core-shell structure

Core-shell Ті5Si3-Mo powders were successfully synthesized by reducing of ammonium molybdate (para) tetrahydrate with hydrogen and glycerol, respectively. As a result, the Ti5Si3 core was coated with submicron and nanosized Mo particles. The morphology and microstructure of the synthesized powders were studied scanning electron microscopy along with local chemical analysis. Phase analysis was performed using X-ray diffraction. The synthesized powders were densified by spark plasma sintering (SPS) at a temperature of 1500 °C. It was shown that powders with a core-shell structure are densified up to a temperature of 1330 °C, while the mechanical mixture of commercial powders at this temperature only begins to densify. The hardness (HV20) of the obtained composites was also investigated. Compressive strength investigation at room temperature shows 5.5 % plastic strain and ultimate strength of about 3 GPa as well as fractographic studies have shown the presence of a pseudo-brittle fracture mechanism for the metal matrix composite (MMC), which was sintered by SPS of the core-shell Ti5Si3-Mo powder synthesized by reduction with glycerol.

Powder casting of polyetheretherketone and polyphenylene sulfone: Sintering

Systematic studies of the influence of the basic powder characteristics and its sintering conditions on the physical and mechanical properties of samples intended for the implementation of the technology of powder injection molding of products from typical heat-resistant high performance engineering polymers - crystallizing polyetheretherketone (PEEK) and amorphous polyphenylene sulfone (PPSu) - were carried out. Polymers with different MW were synthesized as initial materials and powders with different sizes and bulk density were obtained. The influence of these parameters on the nature of powder sinterability and, as a consequence, on their elastic modulus and tensile strength was shown. Optimum characteristics for bulk density and sintering temperature were established, which provide maximum values of mechanical characteristics of the molded samples. The results of the fundamental research conducted allowed us to produce two typical products for biomedicine - an intervertebral cage (an implant replacing a removed vertebra) and a blood dialyzer part.

An economically viable hybrid additive manufacturing process for the fabrication of hierarchically controlled porous biodegradable Fe-Mn scaffolds

The present work aims to develop a novel hybrid additive manufacturing (AM) route for fabricating biodegradable hierarchically controlled porous (HCP) Fe-Mn alloy-based scaffolds. Specifically, a systematic combination of polymer AM and loose powder sintering was used. The morphological, mechanical, magnetic and electrochemical properties of the Fe-30Mn scaffold were evaluated and compared with pure Fe. Proper bonding of particles with some random porosity was observed in the sample. XRD spectrum shows the presence of austenite (γ) and martensite (ε) phases in the sample. The prepared Fe-30Mn samples exhibited porosity = 23.08%, compressive yield stress = 127.28 MPa, modulus of elasticity = 25.9 GPa and corrosion rate = 0.75 mmpy. Moreover, the Fe30Mn sample showed weak magnetic properties, thereby making it MRI-friendly. Better properties of the prepared Fe30Mn sample as compared to pure Fe with close compatibility to the human bone were obtained. Additionally, complex structures of Fe30Mn using the developed methodology were fabricated to establish the efficacy of the process for biodegradable implant application.

Experimental investigation of sinterability of PVA-coated Magnesium powders via mechanical milling using Electric Field-Assisted Sintering Technique

Experimental investigation of sinterability of PVA-coated Magnesium powders via mechanical milling using Electric Field-Assisted Sintering Technique

Powder‐Sintered Hierarchically Porous PMMA with Optimal Pore Parameters for Passive Daytime Radiative Cooling

AbstractPorous radiative cooling polymers have drawn significant attention for passive daytime cooling due to their desirable cooling performance and easy scalability. Since optimal pore parameters (i.e., pore diameter and porosity) will enhance light scattering, polymethyl methacrylate (PMMA) powders are sintered to fabricate samples with different pore parameters by the one‐step full‐dry powder sintering method. These samples have a hierarchically porous structure with pore diameters <5.0 µm. The most porous sample has 43% porosity, 0.964 reflectance in the 0.3–2.5 µm wavelength range, and 0.967 emittance in 8–13 µm wavelength range (which is the atmospheric window). The measured cooling temperature difference decreases when the porosity is low for hierarchically porous PMMA with similar pore size distribution. The high sub‐ambient cooling temperature reduction provided by hierarchically porous PMMA with optimal pore parameters is due to high solar reflectance when illuminated by the sun. Similar cooling trends are evident when sunlight is simulated by a Xenon lamp and an optical filter. The powder‐sintered hierarchically porous PMMA with optimal pore parameters can be an excellent radiative cooler for passive daytime cooling applications.

Enhancing the toughness of Wf/W composites by modifying the fiber/matrix interface utilizing AlN-covered Wf

In this study, short tungsten fibers (Wf) were covered with AlN to modify the fiber/matrix interface in short tungsten fiber-reinforced tungsten matrix composites (Wf/W) fabricated by Fe-activated sintering. During the densification process, an intact and continuous AlN interlayer formed at the fiber/matrix interface through the effective sintering of the AlN powders covering the Wf surface. The AlN interlayer stably existed between the fibers and the matrix without any significant interfacial reactions, leading to relatively weak bonding at the fiber/matrix interface. Based on the extra energy dissipation mechanisms, the composite exhibited typical pseudo-ductile behavior and an increase of 80.35 % in fracture toughness compared to the W(Fe) material. The pseudo-ductile behavior increased the fracture surface area and reduced the stress intensity at the crack tip, resulting in a remarkable toughening effect on the composite.

Achieving high strength and ductility of titanium matrix composite reinforced with networked TiB via SPS sintering of core-shell powder and accumulative hot rolling

Achieving high strength and ductility of titanium matrix composite reinforced with networked TiB via SPS sintering of core-shell powder and accumulative hot rolling

Flash Sintering of Bimetallic Assemblies for Turbine Disks in Next‐Generation Jet Engines

René 77 and another advanced powder metallurgy nickel‐based superalloy are flash‐sintered and joined to produce a dual‐alloy assembly. This innovative process allows for the sintering of powders to achieve high relative densities or the formation of solid joints in a shorter time than is feasible with conventional diffusion bonding techniques. Examination of the microstructure after heat treatments reveals that diffusion and recrystallization phenomena can modulate the transition zone. The creep properties of both alloys, evaluated using stress relaxation tests, do not seem to differ by more than an order of magnitude, while the higher thermal stability of René 77 compared to Alloy B at 800 °C tips the scales. In tension, base materials show very high properties, while bimetallic specimens exhibit at least higher properties than René 77. However, failure occurs at the bond at high temperatures due to the formation of an oxide film during the bonding process. These encouraging results illustrate the potential and constraints of the flash‐sintering process for producing dissimilar assemblies, which may enhance the properties of next‐generation aero‐engine turbine disks.

Quantitative control of interfacial structure and thermal conductivity between diamond and copper via thermal diffusion of alloying element

The thermal property of diamond/metal composites mainly depends on the chemical bonding and structure of interfacial layers between two heterogeneous materials. To improve the thermal property of the diamond/metal composites, a metallic carbide layer that bridging both crystal structure and thermal transport of heterogeneous interfaces is required, though the formation mechanism of such carbide interfaces during powder sintering remains under debate, particularly for the scenario of varying thermal diffusion. Here, systematic experiments of diamond/Cu–Cr composites have been conducted to unravel the effects of two important variables for thermal diffusion, temperature (800–1025 °C) and holding time (5–60 min), on the growth of chromium carbide interfaces and the resulting thermal conductivity. It is found that the main characteristics of chromium carbide layer is more related to the holding time, that is, prolonged thermal diffusion. The extraction of diamonds in as-sintered composites allows a detailed quantification of coating efficiency and crystallographic-facet-dependence of chromium carbide interfaces during diamond/metal reaction at varying temperature and holding times. It is found that the prolonged thermal diffusion is not as expected to deteriorate the thermal conductivity, and leads to a more densified structure with highest thermal conductivity instead (∼577 W/(m·K)). Furthermore, thermal diffusion of diamond/metal reaction is discussed based on theoretical models. We theoretically demonstrate that long thermal diffusion could enhance the thermal diffusivity for the composites and achieve ∼90.8% of theoretical thermal conductivity predicted by the Maxwell-Eucken model.

Reaction-sintered highly transparent MgGa2O4 ceramics with enhanced dielectric properties

Reaction sintering of MgO and Ga2O3 powders was first used to prepare MgGa2O4 transparent ceramics. The microstructural evolution suggested that the negligible volume change resulting from the solid-phase reaction of MgO and Ga2O3, as well as the close and homogeneous arrangement of both fine particles, are the key factors in obtaining pre-sintered ceramics with an ideal microstructure at lower temperature. After a hot isostatic pressing (HIP) treatment, the fully dense ceramic exhibited improved in-transmittance (74.7 %@600 nm, and 85.4 %@4401 nm) and quality factor (Q × f = 168,000 GHz). Due to the combination of high transparency, wide transmission range (6.22 μm at the 60 % transmittance), ultra-low dielectric loss, and near-zero temperature coefficient of resonance frequency (− 3.9 ppm/°C), transparent MgGa2O4 ceramic is suggested to be an ideal optical-dielectric integration material.

Preparation and characterization of quartz ceramic proppant replacing natural quartz sand by solid waste silica fume

AbstractThe improper disposal of industrial wastes will cause environmental pollution and economic losses due to the loss of active ingredients. Solid waste silica fume and pyrolusite powder were used to synthesize quartz ceramic proppant by pelleting and sintering to replace natural quartz sand for unconventional oil and gas exploitation. The effects of pyrolusite powder content and sintering temperature on the apparent density, breakage ratio, and acid solubility of the proppant were thoroughly studied. The phase composition and microstructure of the proppant were characterized by X‐ray diffraction and scanning electron microscopy, respectively. The results revealed that the main crystal phase of the proppant prepared without pyrolusite was cristobalite, while that with pyrolusite was cristobalite and quartz, and the content of quartz phase increased gradually with increasing the pyrolusite content. The addition of pyrolusite remarkably increased the density and improved the performance of the proppant due to the resulting glass phase at high temperatures and the presence of andradite. As adding 20% pyrolusite, the apparent density of the proppant sintered at 900°C was 2.26 g/cm3, while the breakage ratio under 28 MPa closed pressure and acid solubility reached the minimum, 9.89% and 5.3%, respectively, meeting the industrial standard requirements.

Microstructure and Selected Properties of Al2O3 Matrix Composites Fabricated by Pulse Plasma Sintering of Al2O3 and Pre-composite Powder (NiAl–Al2O3)

Paper-related production of composite materials from Al2O3-pre-composite powder (NiAl–10 wt pct Al2O3). PPS allowed for forming ceramic–intermetallic composites. MA produced the pre-composite powder. Six series of composites were made, differing in temperature (1200 °C, 1300 °C, 1400 °C) and content of pre-composite powder (2.5 and 5 wt pct with respect to the amount of Al2O3). Highest hardness was obtained for composite series sintered at 1300 °C. Both series, with various pre-composite powder content, had a value of 20.8 to 20.9 GPa. Samples containing 2.5 wt pct pre-composite powder sintered at 1200 °C were highest KIC value of 4.72 ± 0.34 MPa·m0.5. Interestingly, the same value was obtained in composites containing 5 wt pct pre-composite powder sintered at 1300 °C. For both series with different pre-composite powder content, sintering at 1400 °C obtained the highest strength. For composites containing 2.5 wt pct pre-composite powder, splitting tensile strength value was 255.98 MPa, while for samples with 5 wt pct, pre-composite powder was 264.01 MPaGraphical

Tensile properties and work hardening in Al0.3CoCrFeNi: The role of L12 precipitates and grain size

In this study, we investigate the FCC-Al0.3CoCrFeNi high entropy alloy fabricated via spark plasma sintering of atomized powders, focusing on its mechanical and work-hardening properties across three distinct microstructures: coarse-grained, fine-grained, and fine-grained with L12 nano-precipitates. Using a dislocation density-based model, we analyze the effects of grain size and L12 precipitates on these properties, achieving quantitative agreement between model predictions and experimental tensile and work-hardening behaviors. This exploration highlights the underlying deformation mechanisms at room temperature and their contributions to the strength/ductility trade-off. Significantly, our analysis reveals that twinning in HEAs manifests differently from that observed in steels. Furthermore, the incorporation of L12 precipitates emerges as a critical factor enhancing the alloy's mechanical attributes. Our findings underscore the essential roles of microstructural parameters in tailoring the mechanical properties of HEAs, offering insights that could guide the design of advanced alloys with optimized performance.

The influence of ball milling conditions on the powder characteristics and sintering densification of Mo[sbnd]Cu alloy

Mechanical alloying was utilized to produce Mo-30Cu(wt%) composite powder. The effects of milling conditions on the powder characteristics and sintering densification were investigated. The morphological evolution during the mechanical alloying process can be categorized into four stages: 1-individual Mo and Cu particles, 2-coexistence of Mo particles and blocky MoCu composite particles, 3-coarse irregular composite particles, and 4-refined near-spherical composite particles or lamellar MoCu composite particles, depending on whether process control agent (PCA) is added. The mechanical alloying degree of the MoCu composite powder was deepened gradually from stage 1 to 4, which is influenced by the ball milling parameters. As the milling speed and milling time increase, the lattice strain and the alloying degree of the MoCu composite powders increase while the grain size of molybdenum particles decreases, which is conducive to accelerating the sintering density. Among these ball milling parameters, an elevated milling speed notably accelerates the mechanical alloying process and the sintering density. Under the milling speed of 600 r/min, ball to powder ratio (BPR) of 10:1, and milling time of 4 h, the grain size, lattice strain, and average particle diameter of the composite powder were measured to be 48.4 nm, 0.247 %, and 21.04 μm, respectively, with the particle morphology being nearly spherical. The sintered density of the MoCu composite reached 98.1 %, larger than the other composites.

Fabrication of transparent silica glass and evaluation of silica particle dispersibility in silica slurries based on the solubility parameters of the slurry components

Silica particles were dispersed in 11 acrylic monomers at various concentrations. The dispersibility of the silica particles was evaluated based on the viscosity of the slurry. Furthermore, the relationship between the viscosity of the slurry and the solubility parameters (SPs) of the silica particles and acrylic monomers was investigated. When the SPs of the silica particles and acrylic monomers were close, the viscosity of the silica slurry decreased and high concentrations of the silica particles could be dispersed in the acrylic monomers. Therefore, SP can be used for predicting the dispersibility of silica particles. The prepared slurry was then used to fabricate sintered silica glass. Silica slurry was cured through photopolymerization to obtain a green body, which was then heat-treated at 850 °C in air atmosphere and sintered at 1710 °C under vacuum to obtain sintered silica glass. Transparent sintered silica glass with no cracks was obtained using 4-hydroxybutyl acrylate, which has a similar SP to that of silica particles, as a solvent. The obtained sintered silica glass exhibited a transmittance of 92 % at a wavelength of 400 nm. In the ultraviolet region, light absorption originated from two-coordinated Si in the glass. The absorption spectrum in the infrared region showed an extremely low peak of the SiOH group, indicating that low-OH silica glass was obtained. Thus, this study provides a new method for fabricating silica glass and provides a method of selecting solvents for the slurries used in powder sintering.