Fast Sintering Research Articles

Constructing n-type Ag2Se/CNTs composites toward synergistically enhanced thermoelectric and mechanical performance

Silver selenide (Ag2Se) is emerging as an intriguing material for thermoelectric refrigeration and energy harvesting at near room temperature. To promote the practical applications of Ag2Se, it is imperative to further depress its lattice thermal conductivity (κL) and enhance its mechanical properties. Herein, we develop a nanocompositing strategy toward both enhanced thermoelectric and mechanical performance. Through in situ solution synthesis combined with fast sintering, a series of Ag2Se/carbon nanotubes (CNTs) nanocomposites are controllably constructed. Tuning the concentration of CNTs effectively optimizes the transport and mechanical properties simultaneously, with 0.5 wt% as the optimized addition amount: (i) due to the interfacial effects, this optimal sample obtains a substantially low κL of 0.27 W m–1 K–1 and a slightly enhanced power factor of 2.71 mW m–1 K–2 at 375 K, leading to an exceptional peak zT of 0.97 at 375 K and a high average zT of ∼0.89 over 300–375 K; (ii) this composite achieves a yield strength of 76.0 MPa and a compressive strength of 99.5 MPa, which are improved by 77.2% and 13.3% compared to pristine Ag2Se, respectively. This study develops an effective strategy to construct Ag2Se/CNTs nanocomposites, which advances both thermoelectric and mechanical performance.

Flash‐Sintering Mechanism Studied Through Interrupted Experiments

Flash sintering is under research to allow fast, cost-effective and energy efficient sintering of ceramics. In article, number 2001499, by Yoed Tsur and co-workers, an in-house-made system is constructed for quenching flash sintered samples at mid-experiment. The system is helpful in further revealing the nature of the phenomenon. The results untie the link between flash and sintering. (Cover design: Nofar Laor)

Microstructure and properties of FeSi6,5 soft magnetic materials prepared by spark plasma sintering

In this paper, FeSi6,5 (6.5 wt.% Si) soft magnetic materials have been prepared Via a Spark Plasma Sintering (SPS) technique at difference sintering temperatures in the range of 1150 to 1300 °c for 15 min and a heating rate of 100 °c/min. The results show that the density of sintered samples increased with the rising sintering temperature resulted in the enhancement of Vickers hardness and magnetic properities otsintered samples. Hovvever, the highest magnetic saturation (Ms) of 209.6 emu/g and lowest coercivity (Hc) of 1.85 Oe were obtained for the SPSed sample at 1250 °c. In contrast, the sample sintered in vacuum at 1300 °c for 1h with heating rate of 20 °c/min shows the lower magnetic properties due to the lower density and high amount of pores in the structure. The results of research show that the spark plasma sintering route has a high potential of fast sintering Fe-Si soft magnetic materials and for application.

Dielectric, mechanical and thermal properties of ZrO2–TiO2 materials obtained by microwave sintering at low temperature

The sinterability of 3Y-TZP/TiO2 materials using micrometre-sized ZrO2 and nanometre-sized TiO2 (16 wt%) by one-step fast microwave sintering at low temperature (1200–1300 °C) was investigated. Firstly, in situ detailed analysis of the dielectric properties of the material with temperature was carried out in order to measure the capacity of the material to transform microwave energy into heat. Another related parameter associated to microwave sintering is the penetration depth of the microwave radiation into the material, which showed great homogeneity from 400 °C. Secondly, the effect of sintering conditions on microstructure, density, hardness and coefficient of thermal expansion was evaluated. The X-ray diffraction study and microstructural characterization demonstrate that it is possible to obtain fully dense pieces (>99%) by microwave sintering, a condition yielding to a coarse-grained (~1–2 μm), quite hard (~13.7 GPa) 3Y-TZP/TiO2 material. However, the most important feature is the significant reduction of the thermal expansion coefficient (8·10−6 K−1) as compared to that of 3Y-TZP. In addition, the results from conventional sintering at 1400–1500 °C with 2 and 6 h of dwell time are examined and compared. The materials obtained at 1500 °C showed high density with grain size and hardness similar to those obtained by microwave but with a dramatic difference in the power consumption of the sintering cycle, since the materials obtained by microwave used a maximum absorbed power of 120 W and a heating cycle of only 40 min.

In-situ formed nano-pore induced by Ultrasonication boosts the thermoelectric performance of Cu2Se compounds

Herein, we reported an enhanced ZT value of 1.71 is achieved via in-situ formed nano-pore. The nano-pore is mainly in-situ formed by a combination method with self-propagating high temperature synthesis, ultrasonic treatment and spark plasma sintering. The highly non-equilibrium feature of combustion synthesis leads to the large residual stress in the grains. Due to the presence of residual stress in the grains, the ultrasonic treatment breaks the grains into the structure with sub-nanometer scale and high surface energy, which tends to enclose and to form in-situ pores during the fast sintering process. The liquid-like Cu+ and the in-situ formed nano-pore intensify the phonon scattering, suppressing the thermal conductivity to 0.40–0.45 Wm−1K−1 at 873 K for pore-incorporated samples. In comparison with the melting synthesized sample, a remarkable enhancement of ZT value over 16% at 873 K is achieved. In the temperature interval from 473 K to 873 K, the averaged ZT value for Cu2Se with in-situ formed nano-pores reaches 1.10, improved by 32.5% when compared to that of the melting synthesized sample. This work demonstrates that the combination of self-propagating high temperature synthesis, ultrasonic treatment and spark plasma sintering is an effective way to synthesize the samples with in-situ nano-pores and paves a new avenue for improving the thermoelectric performance of the Cu2Se materials.

Microstructure Evolution in a Fast and Ultrafast Sintered Non-Equiatomic Al/Cu HEA

One of the attractive characteristics of high entropy alloys (HEAs) is the ability to tailor their composition to obtain specific microstructures and properties by adjusting the stoichiometry to obtain a body-centered cubic (BCC) or face-centered cubic (FCC) structure. Thus, in this work, the target composition of an alloy of the FeCrCoNi family has been modified by adjusting the Al/Cu ratio in order to obtain a BCC crystalline structure. However, processing conditions always play a key role in the final microstructure and, therefore, in this work, the microstructure evolution of FeCrCoNiAl1.8Cu0.5 HEA sintered by different powder metallurgy (PM) techniques has been investigated. The techniques used range from the conventional PM sintering route, that uses high heating rates and sintering times, going through a fast sintering technique such as spark plasma sintering (SPS) to the novel and promising ultrafast sintering technique electrical resistance sintering (ERS). Results show that the increase in the processing time favours the separation of phases and the segregation of elements, which is reflected in a substantial change in the hardness of the alloy. In conclusion, the ERS technique is presented as a very promising consolidation technique for HEA.

Large-Scale Rapid Laser Sintering of Highly Stretchable Electrodes Using a Homogenized Rectangular Laser Beam.

This study explored the feasibility of a fast and uniform large-scale laser sintering method for sintering stretchable electrodes. A homogenized rectangular infrared (IR) laser with a wavelength of 980 nm was used in the sintering process. A highly stretchable composite electrode was fabricated using silver (Ag) microparticles and Ag flakes as the fillers and polyester resin as the binder on the polyurethane substrate. This laser-sintering method showed a sintering time of 1 sec and a very uniform temperature across the surface, resulting in enhancing the conductivity and stretchability of the electrodes. The effects of the laser power on the electrical and electromechanical properties of the electrodes were investigated. Using stretching, bending, and twisting tests, the feasibility of the laser-sintered stretchable electrodes was comprehensively examined. The electrode that was sintered at a laser power of 50 W exhibited superior stretchability at a strain of 210%, high mechanical endurance of 1,000 repeated cycles, and excellent adhesion. The stretchable electrodes showed excellent bendability and twistability in which the electrodes can be bent up to 1 mm and twisted up to 90° without any damage; thus, they are highly applicable as stretchable electrodes for wearable electronics. Additionally, the Ag composites were explored for use in a radio-frequency (RF) stretchable antenna to confirm the application of the laser-sintering method for stretchable and wearable electronic devices. The stretchable dipole antenna showed an excellent radiation efficiency of 95% and a highly stable operation, even when stretched to 90% strain.

Microstructure and Dry Sliding Wear Behaviors of Microwave-Sintered Al-4.4Cu-0.7 Mg-0.6Si-B4C/nGr Hybrid Composites

In recent years, more advanced mechanical and tribological properties have been needed in aluminum matrix composites due to the increasing variety of applications. For this purpose, second-generation aluminum matrix hybrid composites that have two or more different particle reinforcements are being developed today. In this study, in order to improve tribological and microstructural properties, nano-sized graphite and B4C-reinforced Al-4.4Cu-0.7 Mg-0.6Si aluminum alloy hybrid composites were produced. As a sintering method, the microwave sintering technique, which is one of the fast sintering methods, was preferred to prevent and/or minimize the formation of unwanted reaction products. In Al-4.4Cu-0.7 Mg-0.6Si-B4C/nGr hybrid composites, 4 different (3, 6, 9 and 12 wt %) B4C and 1 wt % nGr reinforcements were used. Raw samples, compressed by the one-way cold pressing method under 600 MPa pressure, were sintered in the microwave oven at 550 °C temperature for 60 min. In XRD analyses, whereas any unwanted reaction product (Al4C3, Al3BC, etc.) was not detected, θ-Al2Cu precipitate formations were detected. In hybrid composites where no graphite agglomeration was observed within the matrix, the highest hardness value (103.9 Hv0.05) was determined in the sample containing 6 wt % B4C and the lowest specific wear rate (0.271 × 10–3 mm3/Nm) was determined in the sample containing 12 wt % B4C.

Microstructural characterization and enhanced hardness of nanostructured Ni3Ti– NiTi (B2) intermetallic alloy produced by mechanical alloying and fast microwave-assisted sintering process

In this paper, the rapid synthesis of nanostructured NiTi–Ni3Ti intermetallic alloy from titanium and nickel powders through mechanical alloying followed by microwave-assisted sintering process was investigated. The sintered samples at different temperatures exhibited major phases of NiTi– B2 and Ni3Ti, and minor phases of NiTi–B19′ and Ti2Ni. The density, porosity and microhardness of the sample varied based on the sintering temperature, in which the highest density and microhardness (~750 H V) were obtained at sintering temperature of 1100 °C. Based on the results of this research, the microwave-assisted sintering can be applied to fabricate Ni–Ti alloys with improved mechanical properties for biomedical applications.

Effects of vanadium and titanium addition on the densification, microstructure and mechanical properties of WC-Co cermets

WC-Co cermets containing Ti and V metallic powders were prepared by ultra-fast microwave heating process. The mixing of WC-5wt%Co containing 5 wt% concentrations of Ti and V was performed by a high-energy mixer mill in ethanol media for 10 min. A fast microwave sintering process was carried out at temperatures of 1400, 1500 and 1600 °C with an average heating rate of 40 °C/min in a graphite bed without any soaking time. The XRD patterns showed WC, TiC and VC crystalline phases as reaction products. The FESEM images demonstrated uniform distribution of formed carbides in the microstructure of WC based cermet. By increasing the sintering temperature to 1600 °C, almost fully dense samples were obtained in both series of composites containing Ti and V. The maximum bending strength (981 ± 10 MPa), hardness (24.7 ± 0.1 GPa) and fracture toughness (8.6 ± 0.1) were measured for WC-Co-Ti hard metal at sintering temperature of 1600 °C.

Microwave hybrid fast sintering of red clay ceramics

AbstractThis work aimed to examine the performance of the hybrid sintering of clay ceramic in a microwave furnace, compared to the sintering process in a conventional furnace. The raw materials were subjected to X‐ray fluorescence, loss on ignition (LOI), X‐ray diffraction, particle size distribution, real specific mass, and thermogravimetric analyses. The red clay ceramic mass was prepared, extruded, pre‐sintered in a conventional furnace at 600°C/60 min, and sintered at temperatures between 700 °C and 1100 °C. The sintering conventional (resistive oven) was carried out for 60 min with a heating rate of 10°C/min. In the microwave furnace, the sintering times were 5, 10, and 15 min, with a heating rate of 50°C/min, with a sintering chamber coated with silicon carbide (susceptor). The sintered specimens were characterized according to linear shrinkage, water absorption, apparent porosity, apparent specific mass, X‐ray diffraction, Raman spectroscopy analysis, spectroscopy analysis in the ultraviolet and visible regions, microhardness, and scanning electron microscopy. The results showed that microwave sintering promoted an increase in the microhardness and apparent specific mass, and reduction in water absorption and apparent porosity values, due to greater densification in the microstructure. The best results occurred for specimens sintered at 1100°C.

Influence of oxygen induced during high-energy ball milling process on the mechanical properties of sintered nickel by SPS

Starting from micrometric pure nickel powder, high-energy ball milling process allows to produce nanostructured agglomerate powders associated with both a decrease of crystallite size and an increase of structural defects. With the help of a fast sintering process, such as the Spark Plasma Sintering technique, dense nanostructured materials can be elaborated. However, a drawback of this approach concerns the powder oxidation preventing the development of a perfectly densified metallic material. A study was conducted on the oxidation characteristics of nickel powders revealing a significant oxidation during milling process not only on the surface but, also, inside the agglomerated particle powder. The origin of oxygen contamination has been identified by thermogravimetric and X-ray photoelectron spectrometer analyses. It was found that achieving the milling under argon confinement makes it possible to limit the surface oxidation of particles. A best compromise between mechanical activation (i.e. reactivity) and powder contamination was obtained under argon atmosphere with slow rotation speeds of the plate and bowls composing the planetary mill. Such condition provides a nanostructured dense material with a significant improvement of the true ductility (ϵ increase from 28 to 38%) without a limited reduction of the mechanical tensile strength (Rm decrease from 740 to 720 MPa).

Liquid phase sintering and properties of Mn0.6Ni0.9Co1.5−xLixO4-LiF thermosensitive ceramics

Low-temperature NTC (Negative temperature coefficient) thermal ceramic material Mn0.6Ni0.9Co1.5−xLixO4–LiF was synthesized by chemical co-precipitation method and prepared by fast and efficient liquid phase sintering (1000 °C, 5 min). X-ray diffraction analysis results show that the addition of sintering aid LiF does not introduce an impurity phase, and 7%LiF-Mn0.6Ni0.9Co1.5−xLixO4 (x ≥ 0.2) only shows a single-phase spinel -phase MnCo2O4 (PDF# 23-1237). The morphology of the microstructure is analyzed by SEM, and the size of LiF-added grains increases significantly. SEM shows that the density becomes higher, and the electrical properties reflect the trend of the overall lower resistivity and confirm increasing density. The grain size of Mn0.6Ni0.9Co1.5−xLixO4-2%LiF increased from 0.89 to 2.14 µm. In addition, the density of the 4%LiF-Mn0.6Ni0.9Co1.1Li0.4O4 sample reached 4.27g·cm−3. Raman spectroscopy explained the Raman vibration peaks of LiMn2O4 and MnCo2O4. The temperature-sensitive material has obvious NTC performance in the temperature range of − 50 °C to 110 °C. A good linear relationship between lnρ and 1000/T exists over the measured temperature region, which is the characteristic of the small-polaron hopping transport. Mn0.6Ni0.9Co1.5−xLixO4-LiF thermosensitive materials are suitable for liquid phase sintering.

Ultra-high frequency induction and conventional sintering of Al-SiO2 composites: A comparative study

Abstract In this study, it was aimed to determine and compare the sinterability of aluminum-SiO2 composites by conventional and fast sintering methods and to examine their tribological properties after the sintering process. For this purpose, 1, 3, 5, 9, and 15 wt.-% SiO2 reinforced aluminum matrix composites were sintered by a conventional and induction sintering method at 600 °C after uniaxial cold pressing under 200 MPa pressure. The sintering was performed for 30 minutes for the traditional method and 5 minutes for induction sintering. After the sintering, the microstructures of the samples were examined, and their sintered densities and hardness were determined. In addition, the tribological properties of the samples were investigated by the pin-on-disc method, and the worn surfaces were examined after the tests.

Fabrication of chromium carbide cermets by electric resistance sintering process: Processing, microstructure and mechanical properties

Chromium carbide-based cermets are suitable for use in abrasive and corrosive environments. This work presents the fabrication of chromium carbide-based cermets by a very fast sintering process: Electric Resistance Sintering. The thermal cycle duration was less than 1 s and without protective atmosphere.Two different compositions were studied: Cr3C2-25NiCr (wt%) and WC-20Cr3C2-7Ni (wt%). Microstructure and crystallographic phases of the initial powders and sintered materials are presented. In addition, hardness and toughness were characterized and compared to conventional materials.One important issue of ERS is the size and homogeneity of the pieces. This work presents the also the fabrication of a mining wear piece and some aspects about scaling up.

Ultra-high frequency induction and conventional sintering of Al-SiO2 composites: A comparative study

Abstract In this study, it was aimed to determine and compare the sinterability of aluminum-SiO2 composites by conventional and fast sintering methods and to examine their tribological properties after the sintering process. For this purpose, 1, 3, 5, 9, and 15 wt.-% SiO2 reinforced aluminum matrix composites were sintered by a conventional and induction sintering method at 600 °C after uniaxial cold pressing under 200 MPa pressure. The sintering was performed for 30 minutes for the traditional method and 5 minutes for induction sintering. After the sintering, the microstructures of the samples were examined, and their sintered densities and hardness were determined. In addition, the tribological properties of the samples were investigated by the pin-on-disc method, and the worn surfaces were examined after the tests.

A comparison between a new Ultra Fast Pressureless Sintering (UFPS) technology and Spark Plasma Sintering (SPS) for Barium AluminoSilicate metastable phase

Two processes to sinter monolithic hexagonal Barium AluminoSilicate (BAS) are compared in this study: Spark Plasma Sintering (SPS) and a new Ultra-Fast Pressureless Sintering (UFPS) technology developed by Galtenco Solutions®. For both, hexagonal BAS was sintered in its thermal stability range (between 1590 °C and 1760 °C). Results demonstrate that it is only possible to manufacture small parts (15 mm diameter/ 5 mm height) of hexagonal BAS with the SPS process. For larger or more complex shapes, a thermal gradient appears in the sample, leading to the partial melting of some of its body. On the other hand, the new UFPS technology enables the successful processing of large parts of hexagonal BAS with similar efficiency to SPS for small parts. This technology offers a better thermal control of the sintering and eliminates the thermal gradient issue that can be found in the SPS technique.

Fast synthesis and sintering of Li5La3Nb2O12 garnet ceramic

In this research, we present a novel synthesis route to obtain a Li5La3Nb2O12 Garnet structure to be used as solid state electrolyte for Next Generation Li-Battery. The Lithium-based ceramic powder was synthesized by Spray Pyrolysis at 800 °C and it was identified the perovskite structure of LiLa2NbO6 by X-Ray Diffraction characterization. The Scanning Electronic Microscopy showed spherical nanostructured particles with average diameter under 600 nm. After Spark Plasma Sintering the obtained pellets had ~89% of density and XRD analysis indicate its Li5La3Nb2O12 Garnet structure after sintering temperatures higher than 900 °C/30 min with a heating rate of 50 °C/min, without any pre or post heat treatment. The Li-conductivity measured by impedance analysis for this pellet was 10−6 S/cm. This new kind of Field Assisted Fast Sintering avoids grain growth, which favors the lithionic conduction and potentiates the use of this material as ceramic electrolytes.

Aluminum titanate based composite porous ceramics with both high porosity and mechanical strength prepared by a special two-step sintering method

In this work, we develop a two-step sintering technology special for porous ceramics to resolve the contradiction between porosity and mechanical strength. It contains a first long-time sintering at the relatively low temperature (T1) and a second fast sintering at higher temperature (T2). Porous ceramics of aluminum titanate-strontium feldspar-mullite (ASM) ternary composite were prepared by this method, and exhibit both high porosity and high mechanical strength. The effects of T1 and T2 on the phase composition, microstructure, porosity, pore size distribution, mechanical strength and thermal expansion coefficient (TEC) of ASM porous ceramics are systematically studied. The sample sintered at T1 = 1400 °C & T2 = 1500 °C shows optimum performance: the porosity, bulk density, and mean pore diameter (D50) are 63.48%, 1.20 g/cm3 and 15.94 μm, respectively; while the flexural strength reaches 9.22 MPa and the TEC is 2.9 × 10−6/K. The two-step sintering technology provides a powerful tool to develop porous ceramics with excellent comprehensive properties.

Susceptor-assisted fast microwave sintering of TiN reinforced SiAlON composites in a single mode cavity

In the present study, 17 wt % TiN reinforced α-β SiAlON composites were sintered at low temperature by susceptor-assisted microwave heating. The effect of TiN addition on dielectrical properties of starting powders, as well as the influence of sintering temperature on phase evolution, microstructure development and mechanical properties of α/β-SiAlON-TiN composites were investigated. The obtained results showed that TiN addition increased the microwave absorbing properties which is reflected in the peak sintering temperature. Thus, the α:β ratio decreased and mechanical properties were improved, especially the fracture toughness of the composites. Furthermore, an estimate of energy consumption during microwave assisted sintering at the laboratory scale is presented. As a result, the highest values for relative density (97.1%), Vickers hardness (13.35 ± 0.47 GPa), and fracture toughness (7.52 ± 0.54 MPa m1/2) were obtained by microwave sintering for 30 min at 1300 °C.