Spark Plasma Sintering Process Research Articles

The microstructure and deformation behavior of W-SiC composites via spark plasma sintering

In this paper, 0.5 wt% SiC nano particles and pure tungsten powders were thoroughly mixed using ball milling, followed by sintering the mixture using Spark Plasma Sintering (SPS) to obtain the W-0.5SiC composite material block. Then, the effect of sintering temperature on the microstructure and mechanical properties of W-0.5SiC composite was investigated. It was found that the tungsten carbide (W2C) and silicon oxide (SiO2) phases formed at the grain boundaris during the sintering process. Besides, the grain size of the composite increased with the increasing sintering temperature. To better understanding the mechanism of the grain growth, parameter fitting was proceeded based on the well-known grain growth power law. The grain growth parameters pointed out that the grain growth of the W-0.5SiC composite during the SPS process was mainly controlled by the surface diffusion. The hardness of 1800 °C sintered W-0.5SiC composite reached 342.2 ± 4.3 HV, and the compressive strength reaches 1417 ± 137 MPa. The digital image correlation technique was used during the compressive test of 1800 °C sintered W-0.5SiC composite to investigate the deformation behavior. The result indicated that the cracks tended to form at the edge of the sample or near the surface. The extension direction was almost parallel to the loading direction and went throughout the entire sample in at most 0.2 s.

An in-situ formed TiC/FeCoNi medium-entropy composite with excellent combination of mechanical and soft magnetic properties

The utilization of conventional Fe–Co soft magnetic materials (SMMs) as essential materials in electric motors and electromagnets is well-established, however, their mechanical properties cannot be further improved. In order to achieve an excellent balance between mechanical and soft magnetic properties, a novel FeCoNi-based medium entropy composite (MEC) reinforced with in-situ synthesized TiC was designed and prepared via mechanical alloying (MA) and spark plasma sintering (SPS). After the SPS process, the developed MEC exhibited a heterogeneous microstructure consisting of ultra-fine face-centered cubic (FCC) grains, micron-sized FCC grains and in-situ nanosized particles. This resulted in exceptional mechanical properties, with a high tensile yield strength of 910 MPa, combined with a total elongation of 10.9%. The superior mechanical properties of the MEC were attributed to dispersion strengthening, hetero-deformation induced (HDI) strengthening and solid solution strengthening. Additionally, the TiC/FeNiCo MEC also exhibited excellent soft magnetic properties, displaying a high saturation magnetization of 141 emu/g and low coercivity of 619 A/m. Therefore, these results demonstrate the potential of the developed MEC to serve as a promising soft magnetic material (SMM) for future applications.

Investigation of microstructural evolution and mechanical properties Al13Fe4 produced by casting and spark-plasma sintering

In this paper, the preparation and evolution of the polycrystalline Al13Fe4 microstructure were investigated during the casting and spark plasma sintering process (SPS). Experimental results showed that an increase in the cooling rate (90–100 °C/min) for both methods of synthesis led to the formation of cracks and chips in the bulk of the material. Cracks during casting are formed by the passage of a peritectic reaction. The high cooling rate does not allow contact melting products to fill the pores that coalesce into cracks. With SPS, the main driving force for the formation of cracks is the effect of the thermal expansion coefficient. The analysis of XRD and results of mechanical testing revealed the maximum tensile micro stresses (425–430 MPa) in samples obtained at a high cooling rate. A decrease in cooling rate promotes the formation of high-density polycrystalline Al13Fe4. It is noted that the material prepared by SPS has a fine-grained structure by using Al13Fe4 powder as the initial material. The highest indicators of flexural strength are 60 ± 10 MPa, Vickers hardness HV = 8.2 ± 0.8 GPa, fracture toughness K1c = 1.5 ± 0.1MPa × m−0.5, modulus of elasticity 180 ± 10 GPa. The fractography of the surfaces after the flexural test has common features of a quasi-brittle trans crystalline fracture with a “river” structure.

Investigation of the Microstructure of Sintered Ti-Al-C Composite Powder Materials under High-Voltage Electrical Discharge.

Dispersion-hardened materials based on TiC-AlnCn are alloys with high heat resistance, strength, and durability that can be used in aircraft and rocket technology as a hard lubricant. The titanium-rich composites of the Ti-Al-C system were synthesized via the spark plasma sintering process. Composite powder with 85% of Ti, 15% of Al, and MAX-phases was processed using high-voltage electrical discharge in kerosene at a specific energy of 25 MJ kg-1 to obtain nanosized particles. This method allows us to analyze the most efficient, energy saving, and less waste-generating technological processes producing materials with improved mechanical and physical properties. An Innova test indentation machine was used to determine the hardness of the synthesized composites. The microhardness of Ti-Al-C system samples was determined as approximately 500-600 HV. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were performed to identify the hard titanium matrix reinforced by intermetallic phases and the clusters of carbides. Three types of reinforcing phases were detected existing in the composites-TiC, Al4C3, and Al3Ti, as well as a matrix consisting of α- and β-titanium. The lattice parameters of all phases detected in the composites were calculated using Rietveld analysis. It was determined that by increasing the temperature of sintering, the amount of aluminum and carbon increases in the carbides and intermetallic phases, while the amount of titanium decreases.

Spark plasma sintering of Al–SiC composites with high SiC content: study of microstructure and tribological properties

The article presents the results of the microstructure and tribological properties of Al–xSiC composites (x = 70 and 90 wt% SiC) produced in spark plasma sintering (SPS). Due to their attractive thermal, physical, and mechanical properties, aluminum matrix composites with high-volume fractions of silicon carbide (> 50%) have become a major area of interest as a potential material for multifunctional electronic packaging and cryogenic applications. The SPS process was carried out in a vacuum atmosphere under various conditions. Composites with a density close to theoretical (96–98%) were obtained. X-ray diffraction and scanning electron microscopy with EDS analysis were used to characterize the microstructure. Mechanical properties were determined by hardness measurements and a three-point bending test. The tribological properties of the composites were determined utilizing a block-on-ring tribotester. As a criterion for wear resistance, weight loss measured under specific friction conditions, that is, depending on the type of material and the applied load, was adopted. The researched materials were characterized by an even distribution of the carbide phase in the matrix. Composites with the highest SiC phase content (90 wt%) had higher hardness (2537 HV1) and flexural strength (242 ± 15 MPa) with worse wear resistance at the same time. The weight loss of this composite was 0.43 and 0.76% for friction under loads of 100 and 200 N, respectively, and was 360 and 270% higher than that determined for the composites with the lower content of the SiC phase (70 wt%). The wear rate was three times higher for the Al-90wt%SiC composites.

Influence of on-off pulsed current pattern on processes during spark plasma sintering of MgB2 superconductor

High density samples (92–94.5 %) of MgB2 were prepared by Spark Plasma Sintering (SPS). The on-off pulsed current patterns of SPS processing were 8–4, 12–2, 24–2, 99–1. Patterns with more on pulses favor formation of a higher amount of the secondary MgB4 phase through the decomposition of MgB2. They also promote enhancement of larger MgO crystallites without a strong increase in the amount of this phase. Densification rate and pressure in the SPS chamber show a similar behavior, but their amplitude varies and the temperatures defining different stages present some shifts. As-revealed differences induced by pulsed patterns impact superconducting properties in a complex manner. An attempt to assess correlations between the pattern and different superconducting parameters is presented.

Effect of silver plating and sintering temperature on the microstructure and mechanical properties of carbon fiber reinforced Cu matrix composites

Recycled carbon fibers are primarily utilized as reinforcement in the production of composite materials, and they have steadily become a hot topic in the twenty-first century. However, the presence of large amount of residual resin, crack damage and graphitized surface layer on the surface of recycled carbon fibers leads to the reduction of their mechanical properties. In this study, Cu matrix composites reinforced with carbon fiber were created using the spark plasma sintering process at 700–850 °C sintering temperature. The surface coating treatment was done to recycled carbon fiber in order to enhance the interfacial bonding between the carbon fiber and Cu matrix, and the ideal surface Ag plating parameters were investigated and established. Results have shown that the Ag coating on the fiber surface diffuses at different sintering temperatures, forming a Ag–Cu solid solution, which has a solid solution-strengthening effect on the substrate. When the sintering temperature is below 800 °C, some Ag atoms will precipitate out of the matrix, forming a small amount of Ag precipitation phase. As the sintering temperature increases, the tensile strength of the composite increases and then decreases, the compressive strength gradually decreases and the flexural strength gradually increases.

Multiphysics Simulation and Experimental Investigation of the Densification of Metals by Spark Plasma Sintering

Multivariant experimental investigations and multiphysics microstructural modeling of the spark plasma sintering process of metallic powders have been performed up to a relative density of approximately 80%. In comparison, the effect of sintering temperature, pressure, and particle size on the interparticle contact area growth and axial shrinkage of cylindrical specimens of copper and nickel particles is measured in laboratory scaled tests. Herein, for the first time all relevant for sintering phenomena are considered simultaneously: the fully coupled thermo‐electro‐mechanical modeling of the spark plasma sintering processes, additionally taking into account for lattice, grain boundary, surface diffusion, electromigration, and thermomigration, has been carried out. The computational analysis of various physical phenomena allows to identify dominant and insignificant mechanisms. The two‐level numerical simulation includes the modeling of the sintering setup at the macroscopic level and the neck formation process in particle chain systems at the microscopic level. The results of the numerical simulations show a very good agreement with the experimental data. Therefore, the impact of electrical and mechanical loads as well as of particle size on microscopic distribution of temperature, inelastic strain, and on densification has been studied by the finite element simulations.

Surface modification of the Al0.1CoCrFeNi high-entropy alloy by solid carburization via isochronal spark plasma sintering

Carburization by spark plasma sintering process is successfully employed in surface modification of Al0.1CoCrFeNi high entropy alloy. The carburized coating has a double-layer structure and contains two types of carbide precipitates (M7C3 and M23C6). The surface Vickers hardness shows a gradient decreasing trend, and the highest hardness is about three times that of the matrix. Nanoindentation tests are performed to investigate the nanoscale mechanical properties of different phases at different distances from the coating surface. The wear resistance of carburized coating is also assessed based on the nanoindentation results. This research results indicate that the hardness and wear resistance of the carburized coating have been greatly improved.

Does flash sintering alter the deformation mechanisms of tungsten carbide?

The study aims at unravelling the effect of fast and ultrafast electric current-assisted sintering on the plasticity of ultrahard binderless tungsten carbide. The small-scale deformation of polycrystalline micropillars obtained from samples consolidated by Spark Plasma Sintering (SPS) and Electrical Resistance Flash Sintering (ERFS) processes was studied. Micropillars, 3 µm in diameter, were prepared by focused ion beam and compressed ex and in-situ at room and high temperatures (700 °C). Electron-transparent lamellas were milled out from the pillars plastically deformed at different strain levels to carry out Transmission Kikuchi diffraction (TKD) and HRTEM analyses. At room temperature, the micropillars show similar mechanical responses under compression, reaching outstanding yield strengths (8–11 GPa) with plastic strain not exceeding 3–5% because of a dislocation-assisted toughening mechanism. At 700 °C, the pillar's yield strength drops to around 1.5–2 GPa accompanied by the relevant temperature-activated plasticity. However, only the pillars prepared from flash-sintered material can be homogeneously deformed up to ≈50%; conversely, those derived from SPS ceramics fail macroscopically at strains of ≈20–25% strain upon the localisation of plastic strain at shear bands.

Thermoelectric Performance of Ca2Si Synthesized by High-Temperature Melting

Ca2Si was successfully synthesized via a high-temperature melting furnace and a spark plasma sintering process, allowing its thermoelectric properties to be studied. High-temperature melting furnaces were utilized to inhibit the volatilization of Ca elements during the preparation stage, ensuring the production of high-purity Ca2Si. The resistivity of Ca2Si increased gradually with rising temperature and reached 12 mΩ·cm at 873 K, demonstrating semi-metallic characteristics. In the temperature range of 323 K–873 K, Ca2Si displayed relatively low total thermal conductivity, from 1.1 to 1.7 W·m−1·K−1. Nevertheless, Ca2Si attained a maximum thermoelectric figure of merit (ZT) of 0.1 due to the atypical behavior and electrical properties of semiconductors. In contrast, Mg2Si achieved a ZT value of 0.32 at 873 K, owing to its exceptional Seebeck coefficient.

Design and experimental investigation of the high-entropy alloys AlCrFeNiCu and AlCrFeNbMo

To improve the service safety of accident-tolerant fuels in nuclear power plants, the high-entropy alloys (HEAs) AlCrFeNiCu and AlCrFeNbMo were designed and prepared through mechanical alloying (MA) and spark plasma sintering (SPS) processes in this work. The phase structures of AlCrFeNiCu and AlCrFeNbMo were predicted and verified. The microstructure, phase structure, and properties of alloy powders and sintered alloy were investigated under various ball-milling conditions. Results show that the phase formation rule of HEA is an empirical criterion that still needs experimental verification. The HEA powder was refined and had good fluidity after MA. Body-centered cubic (BCC) AlCrFeNbMo powder can be prepared at high milling speeds and long milling times, while the structure of AlCrFeNiCu powder was a BCC plus face-centered cubic (FCC) duplex phase structure. The spark plasma-sintered alloy had fine grains (＜1 μm) and a multiphase structure. AlCrFeNiCu was mainly composed of FCC, B2, and a trace of σ phase, while AlCrFeNbMo was composed of BCC, FCC, and σ phase. The density, hardness, compressive strength, yield strength and strain of AlCrFeNiCu and AlCrFeNbMo alloys were 6.54 g cm−3, 447.57 HV, 1727 MPa, 1642 MPa and 15% and 6.32 g cm−3,1188.82 HV, 2183 MPa, 1943 MPa, and 19%, respectively, which are higher than reported for most HEAs that were prepared by SPS. The fracture mechanism is the typical brittle fracture. Because of solution strengthening and precipitation strengthening, AlCrFeNiCu and AlCrFeNbMo have excellent mechanical properties.

Microstructure, mechanical and soft magnetic properties of in-situ TiC reinforced Fe27.5Ni27.5Co45-based medium entropy composites

The insufficient mechanical properties of conventional soft magnetic materials (SMMs) hinder their widespread applications, and unfortunately, traditional strengthening mechanisms could dramatically deteriorate their soft magnetic properties without adjusting the alloy composition. Here, we developed TiC/Fe27.5Ni27.5Co45 medium-entropy composites (MECs) possessing multi-scale microstructure consisting of ultrafine and micron-sized grains by introducing in-situ formed TiC nano particles during the spark plasma sintering (SPS) process. Compared with the precipitate-free Fe27.5Ni27.5Co45 medium-entropy alloy, TiC/Fe27.5Ni27.5Co45 MEC with ∼ 8.7 vol% TiC (noted as Ti5-MEC) demonstrated a significant improvement in compressive yield strength (from 459 MPa to 1114 MPa), attributing to the grain-boundary strengthening and dispersive precipitation strengthening, as well as hetero-deformation induced (HDI) strengthening. Meanwhile, the Ti5-MEC exhibits a high saturation magnetization (Ms) of 153.1 emu/g and a low coercivity (Hc) of ∼ 8.2 Oe, indicating excellent soft magnetic properties, primarily due to the multi-scale microstructure. Our work has demonstrated that engineering multi-scale microstructures in MECs is an effective strategy to achieve desirable combinations of soft magnetic and mechanical properties.

Optimization of Spark Plasma Sintering Technology by Taguchi Method in the Production of a Wide Range of Materials: Review.

This paper reviews the production of sinters using the spark plasma sintering method. SPS (spark plasma sintering) technology has been used for several decades, mainly in laboratories, to consolidate a huge number of both new and traditional materials. However, it is now more often introduced into practical industrial use, with equipment as early as the fifth generation capable of producing larger-size components at competitive costs. Although the mechanism of sintering with the use of this method is not yet understood, the effectiveness of the SPS process for the rapid and efficient consolidation of a wide range of materials with novel micro-structures remains indisputable. With a relatively wide variation in chemical composition, the structure allows the selection of appropriate consolidation parameters for these materials. The influence on the values of apparent density and mechanical properties depends on the parameters of the spark plasma sintering process. In order to achieve a density close to the theoretical density of sinters, optimization of the sintering parameters, i.e., sintering temperature, heating rate, sintering time, pressing pressure and protective atmosphere, should be carried out. In this paper, the optimization of spark plasma sintering of Si3N4-Al2O3-ZrO2 composite was carried out using the Taguchi method. The effects of four sintering factors, namely heating rate, sintering time, sintering temperature and sintering pressure, on the final density were investigated. Optimal sintering conditions were proposed and a confirmation experiment was conducted. The optimal combination of sintering conditions for spark plasma sintering (SPS) of Si3N4-Al2O3-ZrO2 composite for high apparent density was determined as A3-B3-C3-D2. Based on ANOVA analysis, it was found that the apparent density of sintering was significantly influenced by sintering temperature, followed by pressing pressure, sintering time and heating rate. Validation of the developed mathematical model predicting the apparent density of sinters showed close agreement between the predicted response results and experimental results.

Effect of the Europium during spark plasma sintering of yttrium silicate powder

Spark plasma sintering process was used to densify yttrium silicate powder doped with Europium, at temperature of 1673 K. Densification rate was evaluated during spark plasma sintering of yttrium silicate powder doped with 0, 1, 2.5 and 5 Eu weight percent. The activation energy for densification of the powder was determined at early stage of the sintering. After sintering the microstructure was analysed from sintered coupons doped with Europium+3, identifying an yttrium silicate second phase present.

Effect of Sintering Temperature on the Thermoelectric Properties of Ag2Se Fabricated by Spark Plasma Sintering with High Compression

Silver selenide (Ag2Se) is a high‐performance thermoelectric (TE) material near room temperature. This research improves its TE figure‐of‐merit (ZT) by varying the sintering temperatures (423–723 K) in the spark plasma sintering (SPS) process with high compression pressure (300 MPa). The SPS compaction of Ag2Se powders synthesized by wet chemical reaction leads to the fast fusion of particles so that the grain boundaries are hardly visible. Furthermore, the fast fusion causes nanopores at the grain surface and some cracks, particularly at higher sintering temperatures. These featured microstructures decrease carrier concentrations and affect the TE properties significantly. The TE measurements show that increasing sintering temperatures results in decreased electrical conductivity and increased magnitude of the Seebeck coefficient due to microstructural defects. Increasing SPS temperatures also suppresses the thermal conductivity from enhancing phonon scattering by defects. The bulk Ag2Se sample sintered at 723 K shows the best TE performance with the maximum ZT of 0.90 with a slight variation from 300 to 400 K. Thus, the high‐temperature SPS with high‐compression pressure is likely to be the key for fabricating bulk Ag2Se with high TE performance.

Microstructure and mechanical properties of Ti-Zr alloys fabricated by two-step spark plasma sintering from TiH2 and ZrH2 powders

ABSTRACT Ti is well-known for its high strength-to-weight ratio and biocompatibility. It can be alloyed with Zr to improve mechanical properties. Currently, Ti-Zr alloys can be fabricated by powder metallurgy using Ti and Zr powders, although high oxidation reactivity and cost could still be an issue. In this study, premixed TiH2 and ZrH2 powders were used to prepare Ti-Zr binary alloys with different Zr contents of 0–30 mass% ZrH2 via dehydrogenation and sintering by spark plasma sintering (SPS) process. α-Ti and δ-TiH2 phases coexisted in the sintered Ti-Zr alloys, and a characteristic lamellar microstructure was formed. The tensile strength of the Ti-Zr alloys increased with increasing Zr content due to the solid solution effect, grain refinement and the appearance of δ-TiH2 phases, although the elongation was reduced. This study shows that the fabricated Ti-Zr alloys possess controllable mechanical properties, which can be beneficial for biomedical and other engineering applications.

Effect of in-situ formed oxide and carbide phases on microstructure and corrosion behavior of Zr/Y doped CoCrFeNi high entropy alloys prepared by mechanical alloying and spark plasma sintering

The present work has examined the microstructural evolution, thermal stability, hardness, and corrosion behavior of Zr/Y doped CoCrFeNi HEAs prepared through high-energy mechanical alloying followed by spark plasma sintering (SPS) at 1100 °C. The achieved microstructures were investigated by XRD and TEM techniques. The results showed that investigated HEAs consist of an fcc solid solution of CoCrFeNi matrix with in-situ formed Cr–C carbides and Cr/Zr/Y based oxide phases. The SPS processing of CoCrFeNi yielded grain growth to 370 ± 60 nm, while 240 ± 160 nm grain size with bimodal grain size distribution and 165 ± 38 nm grain size were achieved with Zr and Y additions, respectively. The effects of microstructural changes on the hardness and corrosion behaviors of HEAs were also investigated. Compared with 372 ± 15 HV hardness of CoCrFeNi HEA, 445 ± 26 HV and 563 ± 58 HV hardness values were determined with Zr and Y doped HEAs, respectively. The increase in hardness is mainly ascribed to the precipitation strengthening of carbide and oxide phases as well as smaller grain sizes. The corrosion analysis showed that, although the achieved smaller grain sizes and the presence of different oxide types when dopped with Y and Zr impaired the corrosion resistance, the investigated HEAs have reasonable resistance to corrosion when compared to SS304 stainless steel.

Effect of milling time and sintering temperature on the microstructure and binder distribution of spark plasma sintered NbC-Ni cermets

Niobium carbide (NbC) based cermets are emerging as strong contenders to replace conventional tungsten carbide (WC) based cermets for applications involving abrasion and wear resistance due to their superior mechanical, physical, and chemical properties. NbC cermets with various binders have been explored in literature and nickel has emerged as a promising candidate binder material. Mechanical mixing (MM) followed by spark plasma sintering (SPS) has been shown to be one of the effective methods to synthesize NbC-Ni cermets. However, the effect of certain crucial process parameters during the MM + SPS process on the end product have not been established. To address this, the present study reports the effect of ball milling time and the effect of sintering temperature on the microstructure, binder distribution, hardness, and indentation fracture toughness of NbC – 16 vol% Ni cermets synthesized using MM + SPS. Insufficient milling time resulted in inhomogeneous binder distribution in the consolidated cermets and sintering above a certain temperature resulted in complete loss of binder. Therefore, the combination of sufficient milling time and an appropriate sintering temperature was essential to obtain a consolidated cermet with homogeneous microstructure and uniform mechanical properties.

Investigation of consolidation mechanisms induced by applied electric/electromagnetic fields during the early stages of spark plasma sintering

This work aims at investigating the role of the electric/electromagnetic fields generated by the pulsed current applied during Spark Plasma Sintering (SPS) process on the sintering mechanisms. The selected model material was a metallic granular medium composed of microsized particles of pre-oxidized copper. Its electrical behavior and correlated microstructural modifications were studied in two complementary enclosures. First, a demonstrator equipped with a modulable pulsed electric current generator has allowed analyzing, at low temperature and without mechanical loading, the effects related to the application of an electric wave, by controlling and modulating its characteristics (i.e. shape, frequency, amplitude). An abrupt electrical transition, named “Branly effect” from an insulating to a conductive state, is observed in the granular copper medium. The increase of pulses frequency is shown to strongly reduce the critical time to generate the electrical transition. Moreover, a commercial SPS device, with specific electrical and thermal instrumentation, was implemented by varying applied stress and using conductive and insulating dies. The analysis of the electrical behavior coupled with post-mortem microstructural observations allowed to highlight that the coupling between pulsed current and mechanical stress promotes specific mechanisms in SPS. Under high stress, interparticle contact area increase and the insulating oxide layer is damaged by microcracking. The coupling with the flow of the pulsed current involves local overheating and dielectric breakdown, favoring ignition of Branly effect. Micro-welds are formed between particles, creating privileged paths of the pulsed current and initiating densification at low temperature (250 °C).