Electrical Resistance Sintering Research Articles

Properties and prospects for biomedical application of new Ti-Nb-Sn alloys obtained by electrical resistance sintering

Active research of new β titanium alloy compositions is underway. At the same time, new ways of alloy preparation by powder metallurgy methods are being investigated. In this work Ti-35Nb-XSn alloy (X = 0, 4, 6 wt%) were obtained via electrical resistance sintering (ERS) at current intensities of 11 and 12 kA respectively. The influence of alloying element content and process conditions on the alloys structure and properties in the context of biomedical application were investigated.

Machine learning enabled prediction of tribological properties of Cu-TiC-GNP nanocomposites synthesized by electric resistance sintering: A comparison with RSM

In the present study, copper matrix composites were successfully produced through the powder metallurgy route by applying the electrical resistance sintering technique. Copper composites were reinforced with 5 wt. % TiC and different concentrations of GNP (0.1, 0.2, and 0.3 wt. %). Microstructural investigations confirmed uniform dispersion of TiC and GNP micro and nanoparticles in the copper matrix. A sintering temperature of 900 °C resulted in better densification and hardness of the prepared composites. Moreover, ML models were developed to predict the sintered density, hardness, and wear loss of the composites. Further, it was found that Multi-Layer Perceptron outperforms all other ML models with R2 values of 0.975, 0.934, and 0.948 in the prediction of density, hardness, and wear loss of the composites. On the other hand, RSM shows predicted R2 values of 0.8012, 0.8507, and 0.8756.

Electric Resistance Sintering of Al-TiO2-Gr Hybrid Composites and Its Characterization

In the present work, Al-TiO2-Gr hybrid composites were fabricated through a sustainable manufacturing approach, i.e., ERS (Electric Resistance Sintering) technique. In this experimental work, sintering is performed in a high-density graphite die, which also works as a heating element. The green compacts kept in the graphite die are sintered in two ways simultaneously (conduction and resistance heating). This facilitated the accomplishment of the sintering at a lower current (300–500 A). The aluminum (Al) was reinforced with 9 wt. % TiO2 (rutile) nanoparticles and 3 wt. % graphite microparticles to synthesize a self-lubricated high wear resistance material. Mechanical properties such as density, hardness, and wear loss of the Al-TiO2-Gr hybrid composite were investigated. Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were performed for microstructural investigation. The experiments were performed according to the Taguchi design of the experiment, where three input process parameters (temperature, holding time, and sintering load) were taken to fabricate the Al-TiO2-Gr composite. The sintering temperature of 550 °C resulted in the maximum value of mean sintered density (approx. 2.45 gm/cm3). The holding time of 10 min for the sintering resulted in the maximum value of mean sintered density and mean hardness (HRB 53.5). The mean value of wear loss was found to be minimum for the composites sintered at 600 °C for 10 min. The maximum value of the sintering load (800 N) revealed better density and hardness. Worn surfaces and wear debris were also analyzed with the help of SEM images. The sintering temperature of 600 °C resulted in imparting more wear resistance which was proved by smooth surfaces, micro-cutting, and fewer crates, grooves, and smaller pits.

Mechanical alloying and amorphization of Ti75Cu25 alloy

Ti-Cu alloys are used in dental and medical applications, due to their good mechanical properties, corrosion resistance and antibacterial properties. These properties are sensitive to microstructure and can be improved by formation of intermetallic compounds or amorphization of crystalline Ti-Cu powder. This study focuses on the amorphization of Ti75Cu25 powders prepared by mechanical alloying (MA). Ball milling, up to 60 h, of Ti and Cu powders leads to an amorphous structure. Laser granulometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were carried out for different milling times. Future research on consolidation of amorphous powder via electrical resistance sintering will be performed to obtain bulk samples with amorphous phase and/or nanocrystalline phase with Ti3Cu and/or Ti2Cu intermetallic compounds.

Magnetic properties of iron powder sintered by medium-frequency electrical resistance sintering

Medium-frequency electrical resistance sintering (MF-ERS) is a technique that uses the application of pressure and heat, heat coming from the Joule effect, simultaneously to metallic powders. In this study, this technique consolidates commercial iron powders, and the porosity distribution and hysteresis curves of the compacts were analysed. Compact consolidated by conventional powder metallurgy (PM) was compared with the results obtained.

Ultrahigh Temperature Flash Sintering of Binder-Less Tungsten Carbide within 6 s.

We report on an ultrarapid (6 s) consolidation of binder-less WC using a novel Ultrahigh temperature Flash Sintering (UFS) approach. The UFS technique bridges the gap between electric resistance sintering (≪1 s) and flash spark plasma sintering (20–60 s). Compared to the well-established spark plasma sintering, the proposed approach results in improved energy efficiency with massive energy and time savings while maintaining a comparable relative density (94.6%) and Vickers hardness of 2124 HV. The novelty of this work relies on (i) multiple steps current discharge profile to suit the rapid change of electrical conductivity experienced by the sintering powder, (ii) upgraded low thermal inertia CFC dies and (iii) ultra-high consolidation temperature approaching 2750 °C. Compared to SPS process, the UFS process is highly energy efficient (≈200 times faster and it consumes ≈95% less energy) and it holds the promise of energy efficient and ultrafast consolidation of several conductive refractory compounds.

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

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.

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.

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.

Nickel Porous Compacts Obtained by Medium-Frequency Electrical Resistance Sintering.

A commercially pure (c.p.) nickel powder was consolidated by Medium-Frequency Electrical Resistance Sintering (MF-ERS). In this consolidation technique, a pressure and the heat released by a high-intensity and low-voltage electrical current are concurrently applied to a metal powder mass. A nickel powder with a high tap porosity (86%) and a low applied pressure (only 100 MPa) is chosen in order to be able to obtain compacts with different levels of porosity, to facilitate the study of the porosity influence on the compact properties. The influence of current intensity and heating time on the global porosity values, the porosity and microhardness distribution, and the electrical conductivity of the sintered compacts is studied. The properties of the compacts consolidated by MF-ERS are compared with the results obtained by the conventional powder metallurgy route, consisting of cold pressing and furnace sintering. A universal equation to describe the porosity influence on all the analyzed properties of powder aggregates and sintered compacts is proposed and validated.

Influence of Processing Parameters on the Conduct of Electrical Resistance Sintering of Iron Powders

The influence of the applied pressure and electrical parameters on the macrostructure of specimens consolidated by the medium-frequency electrical resistance sintering technique (MF-ERS) is analysed in this work. This technique is based on the application of pressure to a mass of conductive powder that, simultaneously, is being crossed by a high intensity and low voltage electric current. The simultaneous action of the pressure and the heat released by the Joule effect causes the densification and consolidation of the powder mass in a very short time. The effect of the current intensity and heating time on the global porosity, the porosity distribution, and the microhardness of sintered compacts is studied for two applied pressures (100 and 150 MPa). For the different experiments of electrical consolidation, a commercially available pure iron powder was chosen. For comparison purposes, the properties of the compacts consolidated by MF-ERS are compared with the results obtained by the conventional powder metallurgy route (cold pressing and furnace sintering). Results show that, as expected, higher current intensities and dwelling times, as well as higher pressures and the consolidation of compacts with lower aspects ratios, produce denser materials.

Amorphous Al-Ti Powders Prepared by Mechanical Alloying and Consolidated by Electrical Resistance Sintering

A novel processing method for amorphous Al50Ti50 alloy, obtained by mechanical alloying and subsequently consolidated by electrical resistance sintering, has been investigated. The characterisation of the powders and the confirmation of the presence of amorphous phase have been carried out by laser diffraction, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The amorphous Al50Ti50 powders, milled for 75 h, have a high hardness and small plastic deformation capacity, not being possible to achieve green compacts for conventional sintering. Moreover, conventional sintering takes a long time, being not possible to avoid crystallisation. Amorphous powders have been consolidated by electrical resistance sintering. Electrically sintered compacts with different current intensities (7–8 kA) and processing times (0.8–1.6 s) show a porosity between 16.5 and 20%. The highest Vickers hardness of 662 HV is reached in the centre of an electrically sintered compact with 8 kA and 1.2 s from amorphous Al50Ti50 powder. The hardness results are compared with the values found in the literature.

Simulation of the Electrical Resistance Sintering of Hardmetal Powders

The simulation of the electrical resistance sintering (ERS) of hardmetal powders has been studied. The ERS process can produce a quick consolidation of electrical conductive powders by the simultaneous application of pressure and electrical current. A model of the process has been developed, integrating three actions, namely, thermal, mechanical and electrical, and taking into account the nature of both the powders and the die where powders are placed. The model has been implemented in COMSOL Multiphysics, a finite element commercial program. This paper deals with the model fundamentals and hardmetal particular aspects, such as modelling properties of mixed powders and its thermal behaviour. Other parameters in the model have been tuned to optimally fit the initial experimental data. To check simulation results, measurable parameters have been monitored during experimental tests with WC–6 wt% Co. Once the model was completed and put to work, results are discussed.

Modelling and Simulation of the Electrical Resistance Sintering Process of Iron Powders

In this paper, the process known as Electrical Resistance Sintering under Pressure is modelled, simulated and validated. This consolidation technique consists of applying a high-intensity electrical current to a metallic powder mass under compression. The Joule effect acts heating and softening the powders at the time that pressure deforms and makes the powder mass to densify. The proposed model is numerically solved by the finite elements method, taking into account the electrical–thermal–mechanical coupling present in the process. The theoretical predictions are validated with data recorded by sensors installed in the electrical resistance sintering equipment during experiments with iron powders. The reasonable agreement between the theoretical and experimental curves regarding the overall porosity and electrical resistance suggests that the model reproduces the main characteristics of the process. Also, metallographic studies on porosity distribution confirm the model theoretical predictions. Once confirmed the model and simulator efficiency, the evolution of the temperature and the porosity fields in the powder mass and in the rest of elements of the system can be predicted. The influences of the processing parameters (intensity, time and pressure) as well as the die material are also analyzed and discussed.

Micro and Nano Silicon Carbide Reinforced Aluminium Matrix Composite Prepared by Conventional and Electric Resistance Sintering Process

Micro and Nano Silicon Carbide Reinforced Aluminium Matrix Composite Prepared by Conventional and Electric Resistance Sintering Process

Ceramic dies selection for electrical resistance sintering of metallic materials

Abstract Processing metallic powders by electrical resistance sintering requires the use of insulating ceramics dies. Selecting the appropriate ceramic material according to the electrical, thermal and mechanical properties is a need. Dies produced with several ceramic materials have been tested during the production of cemented carbide in order to check their behaviour in the process and final product properties. Tialite/mullite, zircon/mullite, zirconium phosphate based ceramic, yttria-stabilized zirconia and sialon, in most cases with modified compositions and shaping processes in order to achieve a high density, have been tested. Dry powder processing by cold isostatic pressing and furnace sintering resulted to be the better process for dies production. The effect of die properties on the produced cemented carbide, and the behaviour and life of the die during the production have been analysed. Very smooth die surface increases the number of cycles withstood during metallic parts production, because of lower extraction stresses, as checked for sialon dies. Zirconium phosphate based dies, with low thermal conductivity, show the most densified hard metal parts surface.

Consolidation by MF-ERS of mechanically alloyed Al powder

The aim of this work is to study the viability of producing, by medium-frequency electrical resistance sintering (MF-ERS), compacts from mechanically alloyed aluminium powders. The MF-ERS process was carried out using different values of current intensity (6, 8, 10 and 11 kA) and dwelling (heating) times (400, 700 and 1000 ms). Results were compared with compacts processed by the conventional cold pressing and sintering route (850 MPa and 650 °C-1h). Depending on the processing route different properties were obtained. The final porosity of the MF-ERS compacts (23.6–7%) can be as low, under the tougher tested sintering conditions, as that of the conventionally produced compacts (6%). The compacts obtained by MF-ERS are less ductile, with lower compression strength than that obtained by the conventional route. Furthermore, a similar electrical resistance and higher microhardness can be reached by the MF-ERS process, despite the duration of the consolidation process is only a fraction of that of the conventional process.

Fracture toughness of cemented carbides obtained by electrical resistance sintering

The unique combination of hardness, toughness and wear resistance exhibited by WC-Co cemented carbides (hardmetals) has made them a preeminent material choice for extremely demanding applications, such as metal cutting/forming tools or mining bits, in which improved and consistent performance together with high reliability are required. The high fracture toughness values exhibited by hardmetals are mainly due to ductile ligament bridging and crack deflection (intrinsic to carbides). In this work two WC-Co grades obtained by using the electric resistance sintering technique are studied. The relationships between the process parameters (cobalt volume fraction, sintering current and time, die materials, etc.), the microstructural characteristics (porosity, cobalt volume fraction, carbide grain size, binder thickness and carbide contiguity) and mechanical properties (Vickers hardness and fracture toughness) are established and discussed. Also the presence of microstructural anisotropy and residual stresses is studied. The sintering process at 7 kA, 600 ms and 100 MPa, in an alumina die, followed by a treatment of residual stress relief (800 °C, 2 h in high vacuum), allows to obtain WC-Co pellets with the best balance between an homogeneous microstructure and mechanical behaviour.