Sintering Behavior Research Articles

Al2O3f/Al2O3 composites with high bending strength prepared via a MnO2 modified slurry impregnation method

The limitations of oxide/oxide ceramic matrix composites lie in the need to improve their mechanical properties. It is challenging to reconcile the conflict between matrix densification at high temperature and the potential thermal damage to fibers. The concept of using element doping to control the sintering behavior of matrix was initially applied to prepare alumina-based ceramic matrix composites (CMCs). To lower the sintering temperature of the Al2O3 matrix, MnO2 dopant was used as a sintering aid. As a result, the thermal damage to alumina fibers was decreased, and the mechanical properties of the composite were significantly enhanced. The effect of MnO2 content on the bending strength and micro-morphology of the composite was investigated. The composite exhibits optimal mechanical properties with a 0.01 wt% MnO2 doping, and its bending strength is approximately 405 MPa. The investigation aimed to determine the mechanism by which the fluctuation in micro-mechanical properties of the composites with different MnO2 contents. After the thermal aging at 1000℃ for 500 h, the bending strength of the N610/Al2O3-0.01 composite decreases to 297 MPa. The evolution and mechanism of thermal aging damage have been studied.

Sintering of Si3N4–SiC–MoSi2 composites additively manufactured by Multi Material Jetting

AbstractThe aim of this work was to investigate the sintering behavior of Si3N4–SiC–MoSi2 composites manufactured by the Multi Material Jetting (MMJ) process. Therefore, electrically conductive and insulating Si3N4–SiC–MoSi2 composites were printed using MMJ. Samples were sintered in a gas‐pressure furnace at 6 and 31 atm, respectively. The density, microstructure, and crystalline phase composition were investigated, and the results discussed regarding the phase stability of the Si3N4–SiC–MoSi2 composites. The results show that the nitrogen pressure must be set carefully to avoid the formation of Mo5Si3 or Mo4.8Si3C0.6 on the one hand and to prevent the decomposition of the phases into a Si‐containing melt on the other.

Microstructure and Properties of Hot Pressing Sintered SiC/Y3Al5O12 Composite Ceramics for Dry Gas Seals.

Silicon carbide (SiC) ceramics with high bending strength were prepared by hot pressing sintering (HPS) with yttrium aluminum garnet (Y3Al5O12, YAG) as sintering additive, and the effects of YAG content and sintering temperature on the sintering behavior, microstructure and mechanical properties of SiC ceramics were investigated in detail. The uniform distribution of YAG to form a liquid phase and the driving force provided by hot pressing sintering decrease the sintering temperature, improve the densification of SiC ceramics, and refine the crystal size. By means of suitable sintering conditions with the additional amount of YAG of 5 wt%, the sintering temperature of 1950 °C and a pressure of 30 MPa, the resultant SiC/YAG composite ceramics possesses high sintering and mechanical properties with the relative density of 98.53%, the bending strength of 675 MPa, the Vickers hardness of up to 17.92 GPa, and the elastic modulus of 386 GPa. The as-prepared SiC/YAG composite ceramics are promisingly used as the dry gas seal materials in the centrifugal compressors.

Analysis of initial stage of liquid-phase sintering by combined multi-phase-field/discrete-element method

A combined multi-phase-field/discrete-element method in two dimensions is applied to the liquid phase sintering process of blended elemental powders. The boundary migration, diffusion of elements, and phase transformation between two dissimilar particles are calculated using a multi-phase-field method for sintering based on Gibbs energy functions. The sintering shrinkage is computed with the discrete-element method taking account of the neck size and sintering force, which are obtained from a multi-phase-field simulation. In this study, a pair or small cluster consisting of two elemental powders in a binary eutectic alloy is used as a model system. First, the formation of a liquid phase around the contact area between two dissimilar particles above the eutectic temperature of the system, and the motions of the particles due to grain boundary sliding along the liquid films are confirmed. Second, an Sn–Bi system is selected as the real eutectic system, and the sintering behavior of powder compacts with various mixing ratios of Sn and Bi particles is demonstrated. Finally, transient liquid-phase sintering of Sn–Bi system is simulated, that is, the generation and extinction of the liquid phase due to interdiffusion between Sn and Bi particles are calculated.

Interfacial bonding mechanisms of sintered Cu nanoparticles on different metallization surfaces

Cu nanoparticle sintering bonding is a low-cost die-attach method compared with Ag nanoparticles for power electronic packaging. The joint strength highly depends on the surface metallization of the devices. In present study, the interfacial sintering behavior of copper nanoparticle film (CNF) on different metallizations (Au, Ag, and Cu) was studied. The CNF exhibited a superior shear strength (115 MPa) on Cu substrates when sintered at 250 °C-15 MPa, much higher than that on Ag and Au metallized substrates. The interface connection ratio of bondline-substrate showed the same trend as the shear strength. The neck formation at the bonding interfaces showed no orientation preference. The lateral diffusion of Cu atoms on substrates dominated the sintering bonding, rather than the longitudinal diffusion. The Cu metallization showed much faster lateral diffusion than the Ag and Au metallization, which was confirmed by the neck growth of monolayer nanoparticle sintering and the molecular dynamics (MD) simulation.

Investigation of the effects of titanium oxide concentration on the sinterability, microstructural characteristics, mechanical properties, in vitro bioactivity, and cell culture behavior of chicken-derived hydroxyapatite

This study focuses on how titanium oxide (TiO2) in concentrations ranging from 0.5 to 4% by weight added the hydroxyapatite (CHA) made from chicken femur bones’, affects sinterability, microstructural, mechanical, and in vitro bioactivity properties. According to the results of the experiments, it was determined that CHA decomposed into whitlockite, alpha tricalcium phosphate (α-TCP), tetracalcium phosphate (TTCP), and calcium oxide (CaO) phases at different temperatures. Rutile and perovskite (CaTiO3) phases were also found in TiO2 added CHAs in addition to these phases. With increasing sintering temperature of CHA, the diameters and the heights of the samples decreased. Density increased up to 1250 °C and decreased at 1300 °C respectively. while the partial density value showed similar behavior with density and hardness, At 1200 °C, the maximum values of fracture toughness (1.071 MPam1/2) and compressive strength (145.417 MPa) were attained; however, as sintering temperatures increased, these values shifted downward to 0.882 MPam1/2 and 111.096 MPa, respectively. It has been determined that grain growth and decomposition are the underlying factors in obtaining the highest density, hardness, fracture toughness and compressive strength values for CHA at different temperatures. Among the TiO2 added CHAs, the best properties are obtained for CHA-0.5TiO2 sintered at 1300 °C (Density: 3.0057 g/cm3, Hardness: 3.973 GPa, Fracture toughness: 1.583 MPam1/2 and Compressive strength: 170.045 MPa) and the properties of the CHA-TiO2 composite decreased with increasing TiO2 ratio. This is due to the fact that increasing TiO2 has a detrimental impact on CHA’s sinterability behavior and causes it to become more porous and degrade more quickly. It was discovered through in vitro bioactivity and cell culture assays that the addition of TiO2 had a detrimental impact on the proliferation of bone tissues.

Enhancing sintering behavior and conductivity of YSZ electrolyte by co-doping of ZnO and MnO2

This study aimed to enhance the sinterability and conductivity of yttria fully stabilized zirconia electrolyte through co-doping by 2 mol% of ZnO and different contents of MnO2 (0, 0.5, 1, 1.5 mol%) at two sintering temperatures of 1300 and 1400 °C. Phase composition identification, density, microstructure, and conductivity of the samples were evaluated using X-ray diffraction (XRD), Archimedes' method, field emission scanning electron microscopy (FESEM), and electrochemical impedance spectroscopy (EIS), respectively. The XRD results revealed that ZnO and MnO2 are successfully doped in the fluorite structure of YSZ sintered at 1400 °C, and the cubic structure is completely preserved. However, at a sintering temperature of 1300 °C, the (111) peaks of doped samples were slightly split, which implied a slight phase transformation of YSZ from cubic to a tetragonal structure. The co-doped samples, at both sintering temperatures, showed higher relative density and grain size compared with pure YSZ. The addition of 2 mol% of ZnO and 0.5 mol% of MnO2 at 1400 °C increased the relative density of YSZ from 81.6% to 95.1%. The increase in relative density and grain size, while maintaining the cubic structure, caused an increase in the conductivity of the mentioned sample. Compared with pure YSZ, the sample's total conductivity increased from 7.37 to 10.03 S m−1 at 800 °C. The proposed composition showed better sintering behavior, lower activation energy of grain conductivity, and higher conductivity than pure YSZ. This behavior is thought to be due to the facilitating rearrangement of atoms during sintering and an increase in oxygen ion vacancy concentration due to co-doping with the appropriate amount of ZnO and MnO2.

Study on the sintering behavior of the ceramic precursor Daqiuni clay

Daqiuni clay is an aluminosilicate clay with unique properties that make it a promising ceramic precursor. Understanding its sintering behavior is crucial for quality control in manufacturing. This study aimed to investigate the phase evolution, densification process, and reaction kinetics during sintering of Daqiuni clay. A combination of X-ray diffraction (XRD), simultaneous thermogravimetric-differential scanning calorimetry (TG-DSC), scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR) techniques were employed to comprehensively analyse the phase transformations. The densification behavior, apparent activation energies, and reaction mechanisms were elucidated through thermodilatometric analysis conducted at varying heating rates. Four stages were identified during sintering including dehydration, dehydroxylation, mullite formation, and partial melting. The maximum shrinkages at each stage were measured. Kissinger analysis yielded apparent activation energies of 122.90, 258.40, 361.98 and 348.69 kJ/mol for the dehydroxylation, mullite nucleation, mullite growth, and partial melting stages, respectively. The dehydroxylation and partial melting processes followed the mechanisms of 3rd order reaction and 3D diffusion. Mullite formation was a two-step nucleation and growth process following the JMA model. This study clarified the phase evolution of Daqiuni clay during sintering.

Effect of Carbon on Sintering Behavior of Chromite‐Based Ladle Filler Sands

To investigate the effect of carbon on the sintering behavior of ladle filler sands, laboratory experiments are carried out using chromite‐based filler sands and carbon (graphite) powders as well as liquid steel in an inert atmosphere at 1600 °C. It is found that the fine carbon powders result in an increase in angle of repose before sintering. After sintering, the apparent porosity increases with the carbon content in the sands, while the bulk density declines. During sintering with and without liquid steel, the carbon powders in the sands will react with the sand grains, leading to the generation of some gases (CO and CO2) and the increase of liquid phase in the sands. The acceleration of the formation of the liquid phase in the sands would enhance the sintering of the sands. The generated gases can result in many large holes in the sands, and liquid steel is very possible to infiltrate into the sands. To obtain a higher ladle free opening rate, special attention should be paid to carbon addition in ladle filler sands.

Cold sintering of perovskite‐based mixed conducting membrane for oxygen separation

AbstractCold sintering has attracted significant attention as its remarkably rapid densification process at low sintering temperatures leads to considerable energy savings. However, the sintering behaviors of cold‐sintered perovskite ceramics remain poorly understood and lack precise control over material microstructure. Here, we fabricated dense SrCo0.8Fe0.2O3−δ (SCF) ceramic oxygen permeation membranes by cold sintering. Adding an appropriate ratio of sub‐micron SCF particles can better bridge the sintering interspaces between micron particles, generate amorphous phase through “dissolution‐precipitation,” and aid in the initial densification. The average relative density of SCF membranes undergoes a significant increase to 95.9% after cold sintering and post‐annealing at 900°C, which is much lower than the temperature required for conventional high‐temperature solid‐state sintering (>1200°C). The oxygen permeation flux of the prepared SCF perovskite membrane reaches 2.8 mL min−1 cm−2, which proves that this method has the potential to be an excellent sintering technique for dense perovskite ceramic membranes.

Effect of UV irradiation on the densification behavior, microstructure, and microwave dielectric properties of low temperature sintering Al2O3 ceramics

In this paper, Al2O3 ceramics co-doped with 0.3 wt%CuO–0.6 wt%TiO2–0.1 wt%MnCO3 (CTM, the same below) were prepared. The effect of CTM and UV irradiation on the sintering behavior, microstructure, and microwave dielectric properties have been investigated systematically. The results indicate that the sintering temperature of Al2O3 ceramics could be effectively decreased to about 1200 °C by adding 1 wt% CTM. UV irradiation can further increase the density of the Al2O3 ceramics, improve its microstructure and microwave dielectric properties. By using the Al2O3 powders UV irradiated for 15 min as raw materials, CTM co-doped Al2O3 ceramics can sintered at 1200 °C with a high density of 3.93 g/cm3 and a very high Q × f value of 175,086 GHz.

Effects of frequency on the AC flash sintering behavior and microstructure of Ga-LLZO

In this paper, the effects of frequency on the flash sintering behavior and microstructure of Li6.4Ga0.2La3Zr2O12(0.2Ga-LLZO) were investigated. The results showed that an increase in frequency had little effect on the onset temperature, but this increase reduced the duration of the weak current stage the incubation stage. Moreover, this phenomenon led to a decrease in the power loss during the constant current stage. Scanning Electron Microscope images showed that the microstructure was symmetrically distributed, and the uniformity increased with increasing frequency. Finite element simulations and an IR thermocamera were used to analyze the temperatures of the specimens. The symmetric distribution of temperature during the flash sintering process was the root cause. The results of AC impedance spectroscopy showed that when the frequency of flash sintering was ≥ 400 Hz, the ionic conductivity of Ga-LLZO was greater than that of conventional sintering. The results of this work demonstrated the important role of frequency in controlling the microstructures of ceramic materials in flash sintering.

Glass-based sealants for joining α to β’’-Al2O3 in Na–Zn batteries

This study deals with the design and the characterisation of glass-based materials for the hermetic sealing of ceramic components (α-to β’’-Al2O3) in solid-electrolyte cells operating at approximately 300 °C. A silica-based commercially available glass and a newly developed silica-free glass, potentially resistant to corrosion by molten sodium salts, are reviewed and discussed. 25 wt% alumina powder is incorporated into both formulations. The sintering behaviour of the glass systems and their wetting characteristics on alumina are evaluated at the selected sealing temperatures: 900 °C for 40 min (for the silica-based system) and 700 °C for 1 h (for the silica-free system). The viscosity of both glass systems at these temperatures, which is approximately 105 Poise, is deemed suitable for facilitating proper glass flow and bonding with the alumina components. Furthermore, the coefficient of thermal expansion (CTE) of the potential sealant candidates is investigated. The results demonstrate good compatibility between the glass-based systems (CTE ≈ 7–7.6· 10−6 K−1 at temperatures ranging from 100 to 300 °C) and α- and β’’-Al2O3 (CTE ≈ 7.3· 10−6 K−1 within the same temperature range). The microstructural analysis conducted using field-emission scanning electron microscopy (FE-SEM) confirms good thermo-mechanical matching between the glass-based sealants and the alumina ceramic components and that no reaction occurs during the sealing between alumina powder and the glass matrix.

Spontaneous adsorption effect of graphitic carbon nitride nanosheets to improve sintering behavior of yttria-stabilized zirconia microbeads

Yttria-stabilized zirconia (YSZ) is a ceramic material in which the zirconium dioxide structure is stabilized at room temperature by adding yttrium oxide. However, the YSZ formed by the thick film process on a pre-sintered dense substrate suffers from sintering problems such as different sintering shrinkage rates due to phase transitions and thermal conductivity. This in turn can lead to de-bonding, cracking, delamination, and abnormal growth. We prepared a spherical YSZ green body of approximately 38 μm diameter formed by an organic binder based on a sintered YSZ seed with 15 to 20 μm diameter. In addition, the application of two-dimensional g-C3N4 nanosheets that can be adsorbed on the surface and pores of the green body before the sintering process was evaluated. The YSZ green body with adsorbed surface-modified g-C3N4 nanosheets could be synthesized by stable spontaneous adsorption due to zeta-potential attraction onto the surface of zirconia particles in an aqueous solution. Consequentially, the formation of large grains due to abnormal grain growth was reduced as g-C3N4 was adsorbed. The spontaneous adsorption of nanosheets controls the surface diffusion mechanism by sequentially lowering the energy from a high surface energy in the initial stage of sintering. Uniform grain growth thus can be induced according to the activation energy level of the controlled surface diffusion.

Effects of MgO doping concentration on densification and microstructure of flash sintered α-Al2O3 ceramics

The effects of MgO doping concentration on the sintering behavior of Al2O3 ceramics in flash sintering were studied. The relative density, grain size and oxygen vacancies of the flash sintered samples doped with different amounts of MgO were characterized. The results showed that the relative density and grain size increased with MgO concentration up to 0.25 wt%, and then decreased with further increasing MgO content. These were coincident with the changes in oxygen vacancies in the flash-sintered samples. Flash sintering behaviors of 0.25 wt% MgO doped Al2O3 disc were different from those in conventional sintering, where the grain growth was inhibited when the MgO content is 0.25 wt%. The results can be explained by the fact that the higher oxygen vacancies in the flash sintered sample than that in the conventional sintered one, due to the applied electric field/current in flash sintering enhancing the solubility of MgO in Al2O3.

Synthesis, sintering, mechanical properties, and oxidation behavior of (Zr0.5Me0.5)B2 (Me = Ta, Hf) solid solutions

In this work, (Zr0.5Ta0.5) B2 and (Zr0.5Hf0.5) B2 solid solutions are produced in dense form by coupling the Self-propagating High-temperature (SHS) and Spark Plasma Sintering (SPS) routes. A single boride phase solid solution is formed in both cases by SPS (1850 °C, 20 min) from the multiphasic ceramic powders preliminarily obtained by SHS. The use of small amounts of graphite during SPS is highly beneficial to eliminate oxide contaminants (from 14.5–16.0 wt% to 2.1–2.8 wt%), improve powder consolidation (from 87-90 % to 97.5–98 %), and make the operating conditions milder. Better mechanical properties are exhibited by the binary ceramics with respect to ZrB2 produced by SHS-SPS. The presence of Ta makes the performance of (Zr0.5Ta0.5)B2 superior compared to the Hf-containing system, with hardness, Young's modulus, and fracture toughness equal to 22.1 GPa, 636.9 GPa, and 2.46 MPa m1/2, respectively. On the other hand, (Zr0.5Hf0.5) B2 shows higher oxidation resistance in flowing and stagnant air at elevated temperatures.

Fabrication of large cross-section Ti–6Al–4V alloy using EBS-modified POM-based feedstock

Plastic shaping offers a viable method for the formation of complex structures. However, current research primarily focuses on small and medium-sized components, with limited exploration on the forming, debinding, and sintering of complex components with large cross-section. In this study, by mixing spherical Ti–6Al–4V powder with polyformaldehyde (POM)-based binder, three different feedstocks were prepared, varying in powder loadings and modified with ethylene bis-stearamide (EBS) modification. The feedstock properties were studied, and cylindrical samples with a cross-section thickness of 30 mm were fabricated via rheological press molding (RPM) to investigate their debinding and sintering behavior. The results showed that the increase in powder loading increased the feedstock viscosity but reduced the impurity content (C, O). EBS reduced the contact angle between the powder and POM, and increased the viscosity and sensitivity to shear rate changes. Catalytic debinding of the samples was completed in 2 h. After sintering, EBS-modified Ti–6Al–4V h showed uniform sintering shrinkage, microstructure, the highest relative density of 97.10%, a yield strength of 701 ± 5 MPa, and an ultimate tensile strength of 746 ± 13 MPa.

Sintering and crystallization kinetics of bioactive glass 13–93

This study investigates the sintering and crystallization behavior and kinetic of the bioactive glass (BG) 13–93 with nominal composition (in mol%): 54.6 SiO2 - 1.7 P2O3 - 22.1 CaO - 6.0 Na2O - 7.9 K2O - 7.7 MgO. Sintering and crystallization were investigated non-isothermally for various particle size fractions smaller than 315 µm as well as for bulk samples. Densification was not hindered by the presence of crystalline phases across all particle size fractions. Afterwards, wollastonite was found as the dominant crystal phase at higher temperature which resorb primary surface precipitation-like quartz crystallites. The growth direction shifts into volume when the sample surface is nearly covered. The crystal growth rate of wollastonite was calculated from the crystalline surface layer thickness measured during heating. The findings of this study are relevant for the high temperature processing of BG 13–93.

Effect of compaction pressure on sinterability, microstructure and electrical behavior of Ba0.5Na0.48Sr0.02TiO3 system

The microstructure of electroceramics is a highly influencing factor to decide its functionality and applicability. Processing conditions used for the conversion of raw powder of electroceramics to the net product are playing a dominant role to modulate microstructure. In the present attempt, various compaction pressures (5 tons/cm2, 7 tons/cm2, and 9 tons/cm2) are used to densify the powder sample to the pellet. The effect of the pressure on sinterability, microstructure, and electrical behavior is systematically revealed. Ba0.5Na0.48Sr0.02TiO3 (BNST) with optimized composition has been prepared by the sol-gel combustion method. The structure is confirmed by X-ray diffraction and accompanied by Rietveld refinements. The compaction pressure effect on sinterability is systematically studied by revealing variation of relative density as a function of temperature at constant holding time as well as a function of holding time at a constant temperature. The final obtained relative density is found to be strongly affected by compaction pressure. Microstructural changes during the sintering process are closely monitored and found porosity, grain size, and grain size distribution are strongly affected by compaction pressure. That indirectly influenced electrical behavior. Relaxation frequency and activation energy of charge relaxation are also found to be varied with the compaction pressure of the powder samples.

Understanding the sintering behavior of AlCrFeNiTi high entropy alloy via phase field modeling illustration

In this study, a computational approach is employed to understand the densification behavior of a multi-component alloy system during the sintering process by generating a phase field modeling image. First, a single-phase body-centered cubic (BCC) AlCrFeNiTi high entropy alloy (HEA) is prepared via a mechanical alloying (MA) route, and the powder-processed HEA is shown to exhibit dual BCC phases after spark plasma sintering (SPS). Then, phase field modeling (PFM) is used to generate a generalized image and to understand densification behavior during the sintering process. The results indicate that bulk and grain-boundary diffusion take place during the early stage and grain growth of the powder particles starts when the particles interact with their adjacent grains. Subsequently, in the final sintering stage point contacts and necking were observed. This understanding has been presented based on the phase field simulation to explore the different stages of the sintering during the processing.