Electric Sintering Research Articles

Stepwise Current Increment Sintering of Silver Nanoparticle Structures

Owing to its unique properties, silver (Ag) in the form of nanoparticle (NP) ink promises to play a vital role in the development of printed and flexible electronics. Once printed, metal NP inks require a thermal treatment process called sintering to render them conductive. Among the various methods, electrical sintering is a highly selective and rapid sintering method. Here, we studied the electrical sintering of inkjet-printed Ag NP lines via a stepwise current increment sintering (SCIS) technique. In the SCIS technique, the supplied electric current was gradually increased in multiple steps from low electric currents to higher electric currents to avoid thermal damage to the printed Ag NP ink lines. In less than 0.15 s, a line resistivity as low as 6.8 μΩcm was obtained which was comparable with furnace sintered line resistivity of 6.13 μΩcm obtained at 250 °C in 600 s. Furthermore, a numerical model was developed for the SCIS process temperature estimation. The results enabled us to elaborate on the relationship between the Ag NP line resistivity and the process temperature under various electric currents. Under the applied SCIS technique, a stable sintering process was carried out avoiding the conductive ink line and substrate damage.

Special features of manufacturing cutting inserts from nanocomposite material Al2O3-SiC

The article examines the cutting characteristics of the developed composite material based on aluminum oxide micropowders with silicon carbide nanopowder additives obtained with the help of electric sintering. The influence of thermal conductivity of the developed composite Al2O3-SiC based material on the wear and durability of the material in application of cutting tool is examined, and a comparison with the traditional cutting ceramic tool materials is made. Considering that the process of cutting with ceramic inserts is carried out without the cutting fluids, the heat removal improvement from the cutting zone makes it possible to increase the tool life. It is proposed to use the thermomechanical parameter B for a comparative assessment of cutting ceramic composite material characteristics.

Study of the current density of the electrical resistance sintering technique on microstructural and mechanical properties in a β Ti-Nb-Sn ternary alloy

Study of the current density of the electrical resistance sintering technique on microstructural and mechanical properties in a β Ti-Nb-Sn ternary alloy

Low temperature seamless joining of SiC using a Ytterbium film

Monolithic SiC, for the first time, was seamless joined at a low temperature of 1200 °C using electric field-assisted sintering technology. A 300 nm Yb coating on SiC was used as the joining filler to form Yb3Si2C2 via an in-situ reaction with the SiC. A liquid phase was formed by an eutectic reaction between Yb3Si2C2 and SiC. Almost completely seamless joints were formed by the precipitated SiC grains, which were fully consolidated with the SiC matrix with the help of in-situ formed liquid phase, followed by its elimination under the uniaxial pressure. The bending strength of the seamless joint joined at 1500 °C for 15 min was as high as 257.2 ± 31.1 MPa, which was comparable to the strength of the SiC matrix. As a result, the failure occurred in the matrix indicated a sound joint was obtained. The proposed low temperature seamless joining could potentially be used for joining of SiC-based composite.

Master sintering curve of W-Mo-Cu alloy prepared by electric field sintering

Abstract The master sintering curve (MSC) was developed for the densification description and prediction of W-Mo-Cu alloy sintered by lager current electric field sintering. W-Mo-Cu compacts were sintered at the temperature of 975°C, pressure of 30MPa, and heating rate of 25,75,125°C/s, respectively. The MSC of W-Mo-Cu alloy was successfully constructed with the calculated value Q = 110kJ/mol and experimental data (such as shrinkage data and sintering time and temperature) of the compact. The shrinkage response and the densification process of the compact were studied with the MSC. What's more, the densification of the alloy was verified and predicted by the MSC. The results show that the MSC is a promising strategy for predicting the densification evolution of ternary alloy during sintering.

Medium-Frequency Electrical Resistance Sintering of Soft Magnetic Powder Metallurgy Iron Parts

The fabrication of soft magnetic Fe parts by the medium-frequency electrical resistance sintering (MF-ERS) technique is studied in this paper. This consolidation technique involves the simultaneous application to metallic powders of pressure and heat, the latter coming from the Joule effect of a low-voltage and high-intensity electric current. Commercially pure iron powder was used in the consolidation experiences. The porosity distribution, microhardness, electrical resistivity and hysteresis curves of the final compacts were determined and analysed. The results obtained were compared both with those of compacts consolidated by the conventional powder metallurgy (PM) route of cold pressing and vacuum furnace sintering, and with fully dense compacts obtained by double cycle of cold pressing and furnace sintering in hydrogen atmosphere.

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.

Effect of Pressure and Temperature on Densification in Electric Field-Assisted Sintering of Inconel 718 Superalloy.

Electric field-assisted sintering has ubiquitous merits over conventional sintering technology for the fabrication of difficult-to-deform materials. To investigate the effect of sintering pressure and temperature on the densification of Inconel 718 superalloy, a numerical simulation model was established based on the Fleck-Kuhn-McMeeking (FKM) and Gurson-Tvergaard-Needleman (GTN) models, which covers a wide range of porosity. At a sintering pressure below 50 MPa or a sintering temperature below 950 °C, the average porosity of the sintered superalloy is over 0.17 with low densification. Under a pressure above 110 MPa and a temperature above 1250 °C, the sintered superalloy quickly completes densification and enters the plastic yield stage, making it difficult to control the sintering process. When the pressure is above 70 MPa while the temperature exceeds 1150 °C, the average porosity is 0.11, with little fall when the pressure or temperature rises. The experimental results indicated that the relative density of the sintered superalloy under 70 MPa and 1150 °C is 94.46%, and the proportion of the grain size below 10 μm is 73%. In addition, the yield strength of the sintered sample is 512 MPa, the compressive strength comes to 1260 MPa when the strain is over 0.8, and the microhardness is 395 Hv, demonstrating a better mechanical property than the conventional superalloy.

Consolidation of Titanium Powder by Electrical Resistance Sintering: Practice and Simulation

In this work, a commercially pure titanium powder has been consolidated using the Electrical Resistance Sintering (ERS) process. This technique consists in the consolidation of a powder mass by the simultaneous application of pressure (80 MPa, in this work) and heating caused by the passage of a high intensity (3.5-6.0 kA, in this case) and low voltage current (lower than 10 V), during short dwelling times (0.8-1.6 s, in this work). The resulting compacts have been mechanically characterised by measuring their microhardness distribution. The results obtained are compared with the corresponding values of compacts prepared with the same powders following the conventional P/M route of cold pressing and furnace sintering. The results of some simulations are provided to give information about the temperatures reached inside the compacts during the electrical consolidation process.

Large-scale fabrication of all-inkjet-printed resistors and WORM memories on flexible polymer films with high yield and stability

We report on the development of inkjet-printed thin-film resistors using both organic and inorganic ink formulations. The passive devices were manufactured on flexible polymer substrates in ambient condition without the need for a cleanroom environment or inert atmosphere and at a maximum temperature of 150 °C. By using the same manufacturing process, the rapid electrical sintering (RES) method is demonstrated as effective for the fabrication of inkjet-printed, programmable Write-Once-Read-Many (WORM) memories. Several hundred fully inkjet-printed resistors with different parameters were fabricated and subsequently morphologically and electrically characterized with the aim of obtaining statistically significant data. From a manufacturing process viewpoint, the procedures based on inkjet printing herein described are highly attractive: they do not require high temperatures, low pressures, special atmospheric conditions, and any masks, therefore providing a versatile low-cost approach to fabricate passive electrical components and simple circuits useful for the electronic industry. Printing can be carried out at a sufficiently low temperature to avoid damage to the fabric substrate and these devices can be used in a range of applications requiring flexible and conformal devices from embedded passive filters in PCBs to wearable electronics.

Microstructure and magnetic properties of Ni0·75Zn0·25Fe2O4 ferrite prepared using an electric current-assisted sintering method

Using a Ni0·75Zn0·25Fe2O4 nanopowder synthesized by means of a hydrothermal method as a raw material, polycrystalline nickel zinc (NiZn) ferrite ceramics composed of sub-micron grains were successfully prepared via an electric current-assisted sintering method. Temperatures ranging from 800 °C to 950 °C and a dwell time of 20 min were employed. The phase composition and microstructure of the samples were characterized via X-ray diffraction and scanning electron microscopy, respectively. Moreover, the magnetic properties of the samples were investigated using a vibrating sample magnetometer and a ferromagnetic resonance system. The results revealed that each sintered sample was mainly composed of a spinel phase. With increasing sintering temperature, the specific saturation magnetization increased from 71.85 emu/g to 74.58 emu/g, owing mainly to the increase in the relative density and the average grain size of the NiZn ferrites. The coercivity and ferromagnetic resonance linewidth of the ferrite ceramics decreased monotonically with increasing sintering temperature, owing mainly to the magnetostriction coefficient, saturation magnetization, and porosity of the sintered ferrites.

Retracted] XRD Peak Profile Analysis of SiC Reinforced Al2O3 Ceramic Composite Synthesized by Electrical Resistance Heating and Microwave Sintering: A Comparison

Al2O3 with 10 wt.% of SiC ceramic composite is synthesized at 1500°C by electrical resistance heating sintering with a holding time of 5 hours and microwave sintering methods with a holding time of 15 minutes. The samples generated by the two methods are characterized using powder X‐ray diffraction and field emission scanning electron microscopy (FESEM). Experiments with both samples showed that the existence of the α‐Al2O3 and β‐SiC phases in both samples was verified by the findings of XRD pattern on both samples. Microstructure study illustrates that the Al2O3 matrix particles have spherical‐like shape and their average matrix particle size is 67 ± 5 nm for electrical resistance heating sintered sample and 38 ± 5 nm for microwave sintered sample. The lattice strain and crystallite size of Al2O3 matrix were measured using Williamson–Hall (W‐H) methods, which were achieved via the use of XRD peak broadening, based on a diffraction pattern. Three modified W‐H models were used to compute other parameters, including strain (ε) and stress (σ), as well as energy density (u). These models were the uniform deformation model (UDM), the uniform deformation energy density model (UDEDM), and the uniform deformation stress model (UDSM). The average crystallite sizes of α‐Al2O3 attained from these three models of Williamson–Hall (W–H) methods and FESEM analysis are correlated and found very close to each other. In all three models of the W‐H technique, X‐ray diffraction peak profile examination of electrical resistance heating‐sintered and microwave‐sintered Al2O3/10 wt. % SiC ceramic composite reveals that the microwave‐sintered sample has finer crystallite size with less strain.

Obtaining Ceramic and Composite Materials using a Combination of Methods of Self-Propagating High-Temperature Synthesis and Electric Spark Sintering (Review)

Obtaining Ceramic and Composite Materials using a Combination of Methods of Self-Propagating High-Temperature Synthesis and Electric Spark Sintering (Review)

Study of the method of electric pulse plasma sintering of ceramic materials of the Primorsky krai with mechanoactivated additives

Study of the method of electric pulse plasma sintering of ceramic materials of the Primorsky krai with mechanoactivated additives

Retracted] A Comparative Study on Crack‐Healing Ability of Al2O3/SiC Structural Ceramic Composites Synthesized by Microwave Sintering and Conventional Electrical Sintering

This study was conducted to assess and compare the crack‐healing ability of conventional electrical sintered and microwave sintered Al2O3/x wt. % SiC (x = 5, 10, 15, and 20) structural ceramic composites. The crack‐healing ability of both conventional electrical sintered and microwave sintered specimens was studied by introducing a crack of ∼100 µm length by Vickers’s indentation and conducting a heat treatment at 1200°C for dwell time of 1 h in air. The flexural or bending strength of sintered, cracked, and crack‐healed specimens was determined by three‐point bending test, and the phase variations by X‐ray diffraction and SEM micrographs before and after crack‐healing of both the sintering methods were studied and compared. The results show that almost all the specimens recovered their strength after crack‐healing, but the strength of microwave sintered Al2O3/SiC structural ceramic composites has been shown to be better than that of conventional electrical sintered Al2O3/SiC structural ceramic composites. The microwave sintered crack‐healed Al2O3/10 wt. % SiC specimen shows higher flexural strength of 794 MPa, which was 105% when compared with conventional electrical sintered Al2O3/10 wt. % SiC and crack‐healed Al2O3/10 wt. % SiC specimen. It was found by X‐ray diffractogram that before crack‐healing, all the conventional electrical sintered samples have SiO2 phase which reduce the crack‐healing ability and microwave sintered samples with 15 and 20 wt. % SiC show lesser SiO2 phase and 5 and 10 wt. % SiC samples have no SiO2 phase before crack‐healing. However, after crack‐healing treatment, all the samples have distinct SiO2 phase along with Al2O3 and SiC phases. Microwave sintered Al2O3/10 wt. % SiC specimen cracks were fully healed which was evident in SEM micrographs.

Magnetic Field Generated during Electric Current-Assisted Sintering: From Health and Safety Issues to Lorentz Force Effects

In the past decade, a renewed interest on electromagnetic processing of materials has motivated several investigations on the interaction between matter, electric and magnetic fields. These effects are primarily reconducted to the Joule heating and very little attention has been dedicated to the magnetic field contributions. The magnetic field generated during electric current-assisted sintering has not been widely investigated. Magnetism could have significant effects on sintering as it generates significant magnetic forces, resulting in inductive electrical loads and preferential heating induced by overlapping magnetic fields (i.e., proximity effect). This work summarizes the magnetic field effects in electric current-assisted processing; it focuses on health and safety issues associated with large currents (up to 0.4 MA); using FEM simulations, it computes the self-generated magnetic field during spark plasma sintering (SPS) to consolidate materials with variable magnetic permeability; and it quantifies the Lorentz force acting at interparticle contact points. The results encourage one to pay more attention to magnetic field-related effects in order to engineer and exploit their potentials.

Enhanced thermoelectric properties of screen-printed Bi–Sb–Te films on flexible substrate by electrical sintering process

Screen printing is a low-cost solution-based process for preparing thick-film thermoelements, which bridges the technology gap between bulk and thin-film thermoelectric devices. A screen-printed thermoelectric film on a polymer substrate may exhibit moderate flexibility but normally suffer low electrical conductivity due to the presence of porosity or organic residues. In this study, we present a current-assisted sintering process to consolidate screen-printed Bi–Sb–Te (BST) films on a polyimide substrate at the temperature below 350 °C with simultaneous passage of a pulse current of 2 × 103 A/cm2 in peak current density. The electrically sintered BST film shows greatly enhanced electrical conductivity, leading to a 45% higher thermoelectric power factor (20.2 μW/cm⋅K2) than the thermally sintered BST film (13.9 μW/cm⋅K2). The variations of crystal defect concentration, grain size and secondary precipitates in the BST films with increasing pulse current density and sintering temperature are investigated. The influences of grain boundaries and secondary precipitates on carrier scattering behavior and thermoelectric transport properties of the BST films are also discussed.

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.

Joining of Ti-coated monolithic SiC using a SiCw/Ti3SiC2 filler by electric field-assisted sintering

Monolithic SiC, for the first time, was successfully joined using a SiC whisker-reinforced Ti3SiC2 composite (SiCw/Ti3SiC2) filler via electric field-assisted sintering technique. A thin Ti coating layer was formed on the SiC surface to minimize the residual stress at the joint interface by transforming it into a TiC gradient layer. After optimizing process parameters, a joint strength higher than 250 MPa was obtained, which is higher than the other values reported in the literature. Failure occurred at the SiC base rather than the joining interface because of the improved joint strength by the incorporation of SiCw. The addition up to 15 wt. % SiCw in the filler layer improved the joint strength by various strengthening mechanisms. On the other hand, the joint strength was lower with 20 wt. % SiCw addition, indicating the importance of thermal expansion mismatch between SiCw and Ti3SiC2 to obtain a sound SiC joint.

Electron microscopy observation of electric field-assisted sintering of stainless steel nanoparticles

The intrinsic role of electrical current on the electric field-assisted sintering (EFAS) process of stainless steel 316L nanoparticles has been revealed by both ex situ and in situ experiments. A novel device on the Si chip has been designed and fabricated to fit into the sample holder of a transmission electron microscope for these experiments. The evolution of nanoparticle morphology and microstructures during the EFAS process has been studied using scanning electron microscopy and transmission electron microscopy, which has been combined with the simultaneous measurement of the electric voltage and current changes. A preliminary four-stage mechanism for the EFAS process of stainless steel 316L nanoparticles has been proposed based on these experimental investigations.