Sintering Of Compacts Research Articles

Evaluation of Pore-Former Size and Volume Fraction on Tape Cast Porous 430 Stainless Steel Substrates for Plasma Spraying

Porous 430L stainless steel disks made by tape casting with various pore-former sizes and volume fractions were evaluated as substrates for solid oxide cell (SOC) fabrication by plasma spraying. This work reports the substrate properties relevant to the SOC operation of disks made by using extra fine metal powder with dense sintering to minimize the fine porosity between particles. In contrast, the coarse porosity is introduced by the pore former. We found that the 60 μm pore former at a 45 vol% fraction has the best application fit; it gives an adequate gas permeability of 3.11 × 10−13 m2 and an average open pore size of 45.90 μm. Compared to a commercial substrate with a similar porosity perimeter/steel area ratio, the porosity and gas permeability are 1.6 and 3 times higher, respectively. The detected maximum surface pore is 49 μm, allowing gas-tight electrolytes fabricated by plasma spray deposition.

Effect of gradation on thermal and mechanical properties of reaction‐bonded silicon carbide ceramics

AbstractParticle grading is a reliable method to improve mechanical properties of reaction‐bonded silicon carbide (RBSC) ceramics. This work aims to explore the effects of particle grading on thermal and mechanical characteristics of RBSC ceramics. Results showed that the powder grading enabled to increase sintering density of silicon carbide (SiC) ceramics. The use of large particle SiC powder in grading led to a 28% increase in thermal conductivity but a 22% decrease in bending strength. Meanwhile, the addition of finer SiC powder exerted minimal effect on thermal conductivity but noticeably increased bending strength by 10%. Therefore, properly adjusting particle size in grading allows for the control of residual Si content and microstructure, thereby simultaneously increasing thermal conductivity and bending strength of the material.

Bionic structural design and model calculation for high toughness Si3N4f/BNi fibrous monolithic ceramic: A strategy from the fibrous cell and interface

Preeminent mechanical and dielectric performances are demonstrated by covalently bonded Si3N4 ceramics, yet their application range is still challenged because of limited toughness and sintering density. In this work, the Si3N4f/BNi fibrous monolithic ceramic with uniaxially arranged Si3N4 fibers cells separated by BN interfaces were successfully synthesized via hot-pressed sintering based on bionic structural design. The Si3N4f/BNi fibrous monolithic ceramics with bionic structure exhibited flexural strength, fracture toughness, and density of up to 501 MPa, 10.99 MPa m1/2, and 3.43 g/cm3, respectively. The results revealed that bionic structural design enables to significantly increase the toughness of the ceramic without sacrificing its strength. Furthermore, an original model for determining the flexural strength of fibrous monolithic ceramics was proposed, which can account for various shapes of fibrous cells. The findings of this research open up new prospects for achieving competitive mechanical performance of ceramics.

Numerical Simulation and Experimental Analysis for Microwave Sintering Process of Lithium Hydride (LiH)

Dense lithium hydride (LiH) is widely used in neutron shielding applications for thermonuclear reactors and space systems due to its unique properties. However, traditional sintering methods often lead to cracking in LiH products. This study investigates the densification sintering of LiH using microwave technology. A multiphysics model was established based on the measured dielectric properties of LiH at different temperatures, allowing for a detailed analysis of the electromagnetic and thermal field distributions during the microwave heating of cylindrical LiH samples. The results indicate that the electric field distribution within the LiH is relatively uniform, with resistive losses concentrated primarily in the LiH region of the microwave cavity. LiH rapidly absorbs microwave energy, reaching the sintering temperature of 520 °C in just 415 s. Additionally, the temperature difference between the low- and high-temperature regions during the sintering process remains below 5 °C, demonstrating excellent uniform heating characteristics. The microwave sintering process enhances interface migration within the LiH samples, resulting in dense metallurgical bonding between grains. In summary, this research provides valuable insights and theoretical support for the rapid densification of LiH materials, highlighting the potential of microwave technology in improving material properties.

La1-xSrxF3-x: A Solid-State Electrolyte for Fluoride Ion Battery with High Ionic Conductivity and Wide Electrochemical Potential Window

Abstract Fluoride ion conductors are developed for use as solid-state electrolytes in fluoride ion batteries which are one of promising candidates for next-generation storage batteries. Ba-doped LaF3 (La0.9Ba0.1F2.9: LBF) is mainly used as a solid-state electrolyte in fluoride ion batteries. However, room temperature conductivity of LBF is considerably low, on the order of 10-6 S cm-1 and it is still unclear the optimal elements to be doped to LaF3. In this study, we have explored La0.9SrxBa0.1-xF2.9 system (x = 0, 0.01, 0.025, 0.05, 0.1), in which Ba in LBF is substituted for Sr and investigated the composition dependence of ionic conductivity. We elucidate that the higher concentration of Sr without Ba can significantly improve the ionic conductivity, and the maximum ionic conductivity of La0.9Sr0.1F2.9 is 1.5 × 10-5 S cm-1 at room temperature, which is one order of magnitude larger than that of LBF. The higher ionic conductivity of LSF is due to the larger grain size and higher sintering density of LSF compared to LBF, which results in lower grain boundary resistance. The LSF total ionic conductivity of 10-4 S cm-1 can be achieved at 350 K, which significantly lowers operating temperature of fluoride ion batteries down to 350 K.

Exceptional strength-toughness-hardness integrated B4C ceramics with synergistic reinforcement of nano-BN and in-situ ceramic phases

Boron carbide (B4C) ceramics with enhanced mechanical properties were fabricated by incorporating nano boron nitride (nano-BN), obtained through high-energy ball milling (HEBM) using ZrO2 balls as the medium, and utilizing the spark plasma sintering (SPS) technique. During the densification process of B4C/nano-BN composite powders, an in-situ reaction between the B4C matrix and ZrO2 resulted in the formation of ZrB2 ceramic phases at 1200–1300 °C. Additionally, the rapid sintering densification temperature of composites is reduced to 1500–1700 °C, approximately 80 °C lower than that required for pure B4C ceramics. Notably, while maintaining a high relative density (99.5 %), the Vickers hardness, flexural strength, and fracture toughness of B4C ceramics reinforced with synergistic effects of nano-BN and ZrB2 fabricated at 1750 °C are significantly improved to reach values of 36.8 ± 0.15 GPa, 701 ± 12 MPa, and 5.01 ± 0.13 MPa m1/2 respectively; representing an increase of 3.5 GPa (10.5 %), 225 MPa (47.3 %), and 1.72 MPa m1/2 (52.3 %) compared to pure B4C ceramics alone. The multiple reinforcement mechanisms including pinning effects provided by nano-BN and in-situ formed ZrB2 ceramic phases, B4C/ZrB2 grain boundary pressure and intracrystalline pressure within B4C, interlayer dislocations of nano-BN and turbulent layer of B4C/BN boundaries contribute to energy dissipation during fracture processes, such as crack deflection, bridging, propagation hindrance and branching effect; ultimately resulting in exceptional strength-toughness-hardness integrated B4C-based ceramics.

Effect of ultraviolet treatment on soft tissue healing and bacterial attachment to Titania-coated zirconia.

Zirconia is the most promising implant abutment material due to its excellent aesthetic effect, good biocompatibility and corrosion resistance. To obtain ideal soft tissue sealing, the implant abutment surface should facilitate cell adhesion and inhibit bacterial colonization. In this study, pre-sintered zirconia was placed in a suspension of titania (TiO2) and zirconium oxychloride (ZrOCl2) and heated in a water bath for dense sintering. A titania coating was prepared on the zirconia surface and subjected to UV irradiation. The surface morphology, elemental composition and chemical state of each group of samples were analyzed by scanning electron microscope (SEM), X-ray energy spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The responses of human gingival fibroblasts (HGFs) and common oral pathogens Streptococcus mutans (S. mutans) and Porphyromonas gingivalis (P. gingivalis) to modified zirconia were systematically assessed. Our findings demonstrated that the surface of titania-coated zirconia after UV irradiation produced a large number of hydroxyl groups, and its hydrophilicity was significantly improved. Meanwhile, the UV irradiation also greatly removed the hydrocarbon contaminants on the surface of the titania-coated zirconia. The UV-treated titania coating significantly promoted the proliferation, spreading, and up-regulation of adhesion-related genes and proteins of HGFs. Furthermore, the titania coating irradiated with UV could reduce the adhesion, colonization and metabolic activity of S. mutans and P. gingivalis. Therefore, UV irradiation of titania-coated zirconia can promote the biological behavior of HGFs and exert a significant antibacterial effect, which has broad clinical application prospects for improving soft tissue integration around zirconia abutments. &#xD.

Effect of silver morphology on rheology and photopolymerization characteristics of Silver-Hydroxyapatite slurry for Vat Photopolymerization-based 3D printing process

The present work deals with the processing of HA-silver photocurable slurry to make composites using the Vat-photopolymerization process. Slurries with increasing amount of silver addition in the HA-Ag (0, 5, 10, 15%) slurry have been prepared using monomers with photo-initiators and printed successfully. Silver powder used in this study is in the form of flakes and spheres. A shear thinning behaviour of all the compositions of the slurries has been observed which is essential to fabricate defect-free parts. With increase in silver addition to 15 wt%, the viscosity decreased by around 60 % however curing depth was compromised. From SEM micrographs it was observed that HA with silver flakes showed better sintering with sintering density of 95% compared to only HA and HA with spherical silver samples.

Si3N4-Assisted Densification Sintering of Na3Zr2Si2PO12 Ceramic Electrolyte toward Solid-State Sodium Metal Batteries

The solid-state metal battery with solid-state electrolytes has been considered the next generation of energy storage technology owing to its superior safety and high energy density. But, unfavorable ionic conductivity and interfacial problems make it difficult to widely use in practice. In this work, Si3N4 was rationally introduced into the NASICON matrix as a sintering aid, and the influence of Si3N4 on the crystal phase, microstructure, electrochemical and electrical performance of Na3Zr2Si2PO12 (NZSP) ceramic was systematically studied. The results demonstrate that the introduction of Si3N4 can effectively lower the densification sintering temperature of Na3Zr2Si2PO12 electrolyte and enhance the room temperature ionic conductivity of the NZSP to 3.82 × 10−4 S cm−1. In addition, since Si3N4 has a high thermal conductivity and can inhibit the transmission of electrons between the grains of the electrolyte matrix, it will effectively hinder the generation of sodium metal dendrites and relieve the concentration of the heat source. Moreover, owing to the desirable interface compatibility of the Na and NZSP-Si3N4 electrolyte, the Na/NZSP-1150-1%Si3N4/Na symmetric battery exhibits excellent stability, and the electrode/electrolyte interface still maintains good integrity even after long-term cycling. The assembled Na/NZSP-1150-1%Si3N4/Na3.5V0.5Mn0.5Fe0.5Ti0.5(PO4)3 cell manifests an initial specific capacity of 152.5 mA h g−1, together with an initial Coulombic efficiency of 99.8%. Furthermore, after 200 cycles, the battery displays a capacity retention rate of 82%.

Development of Porous Ti64 by Partial Densification in Spark Plasma Sintering for Laminar Flow Control

Development of Porous Ti64 by Partial Densification in Spark Plasma Sintering for Laminar Flow Control

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.

Investigating the influence mechanism of aluminum doping amount on the density and grain size of AZO target through phase-field simulation

This study proposes a three-phase model (primary, secondary, and pore phases) utilizing the phase-field method to simulate sintering densification in AZO targets. The impact of secondary phase content and dimensions on the densification of AZO targets was investigated. The findings indicated that the density of the AZO target exhibited an initial increase followed by a subsequent decline with the augmentation of the secondary phase content and size. Conversely, the grain size demonstrated a continuous reduction. The Brook kinetic equation yields activation energies for grain growth of 607.40kJ/mol, 999.32kJ/mol, and 1093.20kJ/mol for 1wt%, 2wt%, and 3wt% Al2O3, respectively. Furthermore, the viability of the model was corroborated through experimentation. Based on the simulation outcomes, AZO targets doped with 2wt% Al₂O₃ achieved 99.78% densification, an average grain size of 3.92 μm, and a resistivity of 1.38 mΩ·cm.

Enhanced thermal insulation and corrosion resistance in Ni-Fe cermet through incorporation of high-entropy spinel oxides

The influence of high-entropy spinel oxide (HESO) content on the microstructure, electrical conductivity, and high-temperature corrosion resistance of HESO/NiFe cermets were investigated. The results found that the addition of 10 to 30wt.% HESO enhanced sintering densification and thermal insulation, although it also resulted in reduced electrical conductivity. Isothermal oxidation tests conducted at 900 °C for 10hours revealed that cermets containing 30 to 50wt.% HESO exhibited significantly lower weight gains (0.954 to 1.167mgcm⁻²) and oxidation rate constants (0.1057 to 0.1525mg² cm⁻⁴ h⁻¹). Furthermore, static corrosion tests in AlF₃-KF-Al₂O₃ molten salt demonstrated that HESO effectively mitigated the erosion of the metallic phase by the fluoride molten salt. This study holds significant potential by providing new insights for the design of inert anodes for aluminum electrolysis and exploring the practical applications of high-entropy oxide materials.

A Saw Blade Drill Bit with Reduced Heat Loss

We adopt microwave sintering technology prepared a low-cobalt Fe-Co-Cu diamond saw blade bit. The bit can achieve densification sintering which meets the index of diamond saw blade heads. Furthermore, the use of microwave non-pressure sintering significantly shortens the total sintering time and saves more than 20% energy. This environmentally friendly saw blade head can stimulate the development of the sawing industry and would be vastly used in the field of high and new technologies.

Foaming mechanisms in ball milling prepared borosilicate glass powder

Thanks to their exceptional thermal and electrical properties, borosilicate glasses are widely used in chip packaging and electronic pastes. Nonetheless, borosilicate glass powders suffer from the phenomenon of foaming and expansion during sintering process, which greatly affects the sintering densities of the powders and poses limitations to their applications. Herein, we explored the foaming mechanism of borosilicate glasses by ball milling. The foaming of borosilicate glass is due to the adsorption of CO2 from the atmosphere by the glass powder during ball milling. The CO2 forms carbonates on the surface of the glass powder and is released during the sintering process, leading to foaming. Additionally, as the specific surface area of the glass powder increases, its corrosion resistance decreases while its foaming strength increases. The foaming strength of the four glass powders, listed in ascending order, is: SrO-B2O3-SiO2, ZnO-B2O3-SiO2, BaO-B2O3-SiO2 and CaO-B2O3-SiO2. Meanwhile, it was found that the foaming strength could be weakened better by ball milling organic modification method. These findings contribute to a deeper understanding of the glass foaming phenomenon. Furthermore, they offer practical strategies to reduce the foaming and optimize the performance of borosilicate glass-based materials in applications of chip packaging and electronic pastes.

Phase formation, microstructure and mechanical properties of TaB2–SiC composites synthesized by reaction hot pressing: Effects of SiC contents and oxygen impurity

TaB2–SiC composites with 0–20 wt% SiC contents were prepared by reaction hot pressing using Ta, B and SiC powders as starting materials. Densification, constituent phases, microstructure and mechanical properties, namely Vickers hardness, fracture toughness and flexure strength, were evaluated by means of inspection of sintering shrinkage, density measurement, XRD, SEM, TEM, HRTEM, EDS, SAED, indentation and three-point bending tests. Phase formation, including dominant (TaB2, SiC) and minor (TaC, glassy SiO2) phases, was checked by thermodynamic assessment relevant with Ta2O5 and B2O3 impurities introduced into the reaction system by the starting powders. The results showed that mixtures of Ta, B and SiC powders would initiate self-propagating combustion synthesis (SPCS) at about 900 °C; a transient hold at 800 °C for 1 h could suppress this reaction. Volatilization of B2O3 impurity in association with local high temperature due to SPCS helped reduce the TaC and glassy SiO2 minor phase formation. TaB2–SiC composites could reach 99 % relative densities with 3 wt% SiC addition and above. Compositions with <7.5 wt% SiC additions showed uniform dispersion of SiC particles at multi-TaB2 grain junctions while compositions with higher SiC content revealed SiC segregation. Bending strength of 503 MPa and fracture toughness of 6.69 MPa⋅m1/2 could be reached with 7.5–20 wt% SiC addition.

Investigation of phase transformation model, densification mechanism, and mechanical properties of TiH2 powder metallurgy materials

TiH2 has gradually gained attention in powder metallurgy because of its unique properties. This study systematically investigated the porosity, density, mechanical tensile properties, and fracture toughness of sintered samples of TiH2 as a powder metallurgy starting material. The results showed that, compared with hydrogenation-dehydrogenation titanium (HDH Ti), the density, elongation, and fracture toughness of the sintered TiH2 samples significantly improved. In addition, the contributions of grain size, porosity, and oxygen content to the yield strength of the samples are discussed, and the results revealed that a lower oxygen content and porosity are the main reasons for the differences in the mechanical properties between HDH Ti and TiH2. Finally, the experimental results are combined with first-principles calculations and simulations to construct a TiH2 phase transition model. The contribution of H atoms to the TiH2 phase transition energy barrier and activation sintering densification was investigated and elucidated, revealing the TiH2 sintering densification mechanism from the perspective of phase transition. The derived results contribute to a deeper understanding of the intrinsic mechanism of TiH2 activation sintering densification, which is highly important for the development of advanced titanium materials.

Optimization of Ni-Cu binder composition and sintering time for enhanced mechanical properties of Mo alloys via liquid phase sintering

Liquid phase sintering of refractory alloys offers a promising approach to enhance mechanical properties while ensuring cost-effectiveness and near-net shaping capabilities. This study systematically explores the impact of sintering time and Ni-Cu binder composition on densification, shape retention, and mechanical properties of Mo alloys processed via liquid phase sintering. The aim is to identify optimal binder composition and sintering time for low-cost production of dense, near-net-shape Mo alloys with superior mechanical properties. The sinterability of Mo compacts is enhanced as the Ni-Cu ratio increases. However, excessive Ni content induces geometric distortion during sintering. Alloys with Ni-rich binders exhibit two liquids at the sintering temperature, each with differing Mo solubility, resulting in a dual-phase matrix on solidification. Both Cu-rich and Ni-rich binder compositions exhibit brittle δ-MoNi intermetallic compound formation, whose quantity increases with prolonged sintering times. Alloys characterized by low Mo solubility in the matrix, high Mo volume fraction, high Mo grain contiguity, and large dihedral angles demonstrate high structural integrity and resistance to geometric distortion. Conversely, alloys featuring high matrix volume fraction, low grain contiguity, elevated Mo solubility in the binder, and strong Mo-matrix interfaces exhibit enhanced strength, hardness, and ductility. Notably, an alloy with a Ni-Cu ratio of 3:1 sintered for just 30 min at 1420°C demonstrates outstanding mechanical properties—hardness of 410 HV, tensile strength of 920 MPa, and elongation of 9 %—comparable to or better than many previously reported refractory alloys.

Influence of stabilized zirconium dioxide and high hydrostatic pressure on the kinetics of sintering nanopowders of metastable aluminum oxide

The paper presents an analysis of the effect of processing powders with high hydrostatic pressure (HHP) (300, 500, 700 MPa) and stabilized zirconium dioxide (ZrO2 + 3 mol.% Y2O3, (YSZ)) doping on the compaction of metastable nanopowders mixture with γ+θ-Al2O3 + n% YSZ (n = 0, 1, 5, 10, 15 wt%) composition during sintering. The behavior of nanopowders at the initial stage of sintering was studied by dilatometry at a constant heating rate of 5 °C/min, in temperature range from 20 °C to 1500 °C. It has been determined that sintering of compacts occurs in two stages: compaction of γ + θ-Al2O3 (Ⅰ-st stage metastable phases), compaction of the stable α-Al2O3 (ⅠⅠ-nd stage), accompanied by inhibition between them. An “effect of mutual protection against crystallization” of powder mixtures was determined using the X-ray diffraction method. This is characteristic of systems obtained by co-precipitation. A connection between the above mentioned inhibition and an increase in the YSZ additive was found. That, also, correlates to the effect of “mutual protection against crystallization” of Al2O3 – YSZ powder mixtures. A study of the mechanisms and activation energies of γ+θ-Al2O3 + n% YSZ systems’ (n = 0, 1, 5, 10, 15 wt%) sintering depending on the YSZ additive amount and the HHP value showed that a dopant and pressure increase leads to activation energy decrease of the initial sintering stage, and the prevailing sintering mechanism is volumetric diffusion in corundum grains. Also, the work shows that for γ+θ-Al2O3 + ≥5 wt% YSZ systems, the optimal compaction pressure is HHP ≥500 MPa, which corresponds to the transition of the sintering mechanism from grain-boundary diffusion to volumetric diffusion.

Enhanced mechanical properties and oxidation resistance of NbC-Ni cermets via NbN addition

The mechanical properties and oxidation resistance of cutting tool materials are two important factors that can affect their performance. In this work, NbN was used as an additive to improve the mechanical properties and oxidation resistance of NbC-Ni cermets. The results demonstrated that the densification sintering temperature increased with increasing addition of NbN, with the optimized sintering temperature of NbC-Ni cermets containing 10 wt% NbN being 1480 ℃. The incorporation of NbN into NbC-Ni led to the formation of NbCN-Ni cermets. As a result of solution strengthening, the cermet transverse rupture strength (TRS) and hardness were considerably improved. However, the TRS and hardness decreased for the NbC-Ni cermets exceeding 10 wt% NbN owing to the increased porosity and grain growth. With increasing NbN content, the oxidation resistance of NbC-Ni cermets initially increased before decreasing. The best oxidation resistance of NbC-Ni cermets with 10 wt% NbN was due to the higher NbN content and dense structure.