Spark Plasma Sintering Equipment Research Articles

Investigation of the Mechanical and Biological Properties of Ti6Al4V-Cenosphere Porous Composite Made by Spark Plasma Sintering Equipment

Investigation of the Mechanical and Biological Properties of Ti6Al4V-Cenosphere Porous Composite Made by Spark Plasma Sintering Equipment

In situ X-ray diffraction study of a TiO2 nanopowder Spark Plasma Sintering under very high pressure

We investigated the effect of very high pressure on the sintering temperature, phase transition and the grain growth during Spark Plasma Sintering (SPS) of a 15 nm TiO 2 nanopowder. Using in situ synchrotron X-ray diffraction during sintering at 1.5 and 3.5 GPa, we followed the evolution of the crystalline phases and the crystallite size as a function of temperature. In comparison, in the laboratory, SPS experiments were performed on two original facilities: A Paris-Edinburgh press and a high-pressure module adapted to standard SPS equipment. We studied the effect of the pressure on the sintering in the range 76 MPa to 3.5 GPa. We have shown that highly dense nanostructured ceramics can be prepared under very high pressure at low sintering temperatures. At 1 GPa, we limited the grain growth to an average size of 233 nm by heating at only 560 °C, and achieved a relative density of 98%.

Water-Assisted Cold Sintering of Alumina Ceramics in SPS Conditions

A developing energy-saving approach of cold sintering in a pure aqueous medium was applied to the preparation of α-Al2O3 ceramics and performed on spark plasma sintering equipment. The initial γ-Al(OH)3 and γ-AlOOH powders and the cold-sintered ceramics were studied by X-ray diffraction analysis, infrared spectroscopy, thermal analysis, and scanning electron microscopy to reveal the chemical and structural transformations they experienced during the cold sintering. At 450 °C and 70 MPa, initially γ-AlOOH transformed into a fragile α-Al2O3 material. Porous α-Al2O3 ceramics with about 60% porosity were obtained after cold sintering of γ-Al(OH)3 in the same conditions combined with subsequent annealing at 1250 °C for 3 h. The role of water molecules in the studied processes was considered as the enhancement of structural mobility in the cold-sintered material due to its reversible hydroxylation similar to earlier investigated supercritical water actions on the precursors during α-Al2O3 formation. Further improvement of the cold sintering setup and regimens would open prospects in α-Al2O3 ceramics manufacturing by an ecologically benign route.

Research and improvement of SPS spark plasma sintering equipment

Through the functional disassembly study of the pressurization system, vacuum and atmosphere control system, water cooling system and control system of the SPS spark plasma equipment, the problems in the actual production process and the corresponding improvements of the spark plasma sintering (SPS) equipment are also discussed. The shortcomings and its development directions are also proposed to provide sufficient data support for the subsequent research.

Alumina/molybdenum nanocomposites obtained by colloidal synthesis and spark plasma sintering

Alumina/molybdenum nanocomposites were prepared by colloidal synthesis from alumina powder and molybdenum (V) chloride using ethanol as dispersion medium. Modified alumina was calcined at 450 °C in air atmosphere to remove chlorides, and then treated in a tubular furnace at 850 °C under Ar/H2 to reduce the MoO3 formed in the previous stage and obtain Al2O3 with molybdenum nanoparticles on the surface. Three different molybdenum contents were proposed (1, 5 and 10 wt % Mo), and pure alumina was used as reference, that were sintered by spark plasma sintering (SPS) under vacuum atmosphere at 1400 °C for 3 min with an applied pressure of 80 MPa. Composites were characterized by microstructure, hardness, toughness, and three-point bending test. The presence of molybdenum nanoparticles resulted in a fine-grained structure promoted by the presence of molybdenum at grain boundaries and triple points, as well as by the utilization of the SPS equipment. Hardness is at least a 20% greater and fracture toughness 30% larger in the composites than in the monolithic alumina.

Deformation Treatment in Spark Plasma Sintering Equipment and Properties of AlON-based Ceramic

Deformation Treatment in Spark Plasma Sintering Equipment and Properties of AlON-based Ceramic

Overview of Spark Plasma Texturing of Functional Ceramics

This work reports the progress in the preparation of superconducting and thermoelectric lamellar compounds processed by the unconventional Spark Plasma Sintering (SPS). The SPS equipment was modified with the aim of obtaining the textured and dense superconductor Bi2Sr2Ca2Cu3O10,p-type oxide thermoelectric bulk as Ca3Co4O9 and Ca3-xAgxCo4O9/Ag composites respectively. The new process is referred to as Spark Plasma Texturing (SPT). During SPT, the bulk material can freely deform. As a result, inter-grain preferential crystallographic orientation is created. The series of sintered and textured samples using the same Ag content were processed respectively. From the results, we can evidence: (i) the magnetic and/or structural transition around 350 °C, for both series of samples. (ii) The electrical resistivity (ρ) decreases with increasing Ag-substituted or Ag-added. (iii) The Seebeck coefficient (S) of the textured series is higher than that of the sintered series. In the case of the Ag-substituted, S, decreases with Ag content. The optimized composite is found to be Ca2.6Ag0.4Co4O9/8wt% Ag. We can note the remarkable reduction of ρ, and the improvement of power factor values up to 360 μW.m−1.K−2.The superconducting properties of single phased Bi2Sr2Ca2Cu3O10 (Bi2223) consolidated using SPS and SPT will also be discussed.

Phase transformation of alumina induced by high pressure spark plasma sintering (HP-SPS)

Spark plasma sintering of nanocrystalline γ-Al2O3 at very high pressure was investigated up to 5 GPa. A SPS pressure/temperature diagram of α-Al2O3 and γ-Al2O3 phase was plotted. An in-house high pressure spark plasma sintering equipment (HP-SPS) was used. The capabilities and parameters control of this equipment greatly reduced the phase transition and sintering temperatures to obtain ceramics in contrast to conventional high pressure and high temperature sintering (HP-HT). The transition temperature could be lowered to ~500 °C from 1 GPa. The grain growth in ceramic was retained by the HP-SPS sintering. The density was also demonstrated to be optimized with HP-SPS.

Comparison of hot pressing and spark plasma sintering in the densification behavior of indium tin oxide‐borosilicate glass composites

AbstractThe goal of this study was to fabricate borosilicate glass matrix composites with high optical transmittance and high conductivity by forming percolated segregated networks of indium tin oxide (ITO) in the microstructure. ITO nanoparticles and borosilicate glass microspheres were mechanically mixed with ITO concentrations varying from 0 to 2.99 vol%. The mixes were then consolidated using either hot pressing (HP) or spark plasma sintering (SPS). The effects of changing sintering methods, along with varying other processing parameters such as heating rate, maximum temperature, and applied pressure, had surprising and unanticipated effects. Ac impedance spectroscopy (IS), SEM, and EDS results indicated the successful formation of a grain‐like microstructure of the sintered glass using both HP and SPS processing, with the ITO particles segregated to the boundary regions in all samples. IS results indicated percolation threshold values between 0.154 and 0.307 vol% ITO in the HP samples and between 0.307 and 0.764 vol% ITO in the SPS samples, with resistivities as low as 29 (Ω·cm) at 2.99 vol% ITO. Optical properties were dominated by impurities and light scattering at defects such as pores. Contrary to conventional belief, it was found that samples made using SPS required far higher temperatures to fully densify, with all other processing conditions being the same, compared with HP. This behavior was confirmed through repeat tests using different SPS equipment and a wide range of processing conditions.

A SYSTEMATIC PROCEDURE TO STUDY HOT PRESSING AND SPARK PLASMA SINTERING KINETICS

A procedure for data collection and processing was developed to conduct accurate kinetic analysis in pressure assisted sintering techniques, such as hot pressing (HP) and spark plasma sintering (SPS). Densification of MgAl 2 O 4 by SPS was chosen as a model system, where the kinetics were analyzed by utilizing the modified creep equation. Displacement data used in the equation was gathered by path measurement system (PMS) of the SPS equipment. Effects of temperature control accuracy, load cell accuracy and resolution of the PMS on the reliability of collected displacement data were evaluated. Dilution of the data in order to reduce the noise in strain rate values caused by the low resolution of the PMS system, which is only 10 μm, was observed to affect calculated stress exponents (n), significantly. Different n values in the range of 1.7-2.8 in a narrow interval of 83-86 % relative densities were found as a function of dilution degree. On the other hand, differentiating the strain with respect to the time interval of every single 10 μm displacement was shown to provide more consistent results. n values of ≈2.2 with a standard deviation of 0.15 were calculated for the same density intervals.

Morphological characteristics in polycrystalline tungsten diselenide regulating transport properties lead to predominant thermoelectric performance

We studied a polycrystalline p-type WSe2 semiconductor for thermoelectric applications. The polycrystalline WSe2 nanocompound was prepared via a thermal reaction process of tungsten and selenium elements and it was sintered to produce a bulk structure using spark plasma sintering equipment. The resulting bulk specimen showed different morphological aspects, in which we observed irregularly-shaped grains along the direction perpendicular to the sintering pressing direction (i.e., along transversal direction) while finding thin layers along the parallel direction (i.e., along longitudinal direction). The specimen recorded a significantly low longitudinal thermal conductivity possibly because longitudinal phonon transport should be hindered due to the thin layers. Electron transport along the longitudinal direction might not be greatly interrupted by the morphological characteristics because the specimen recorded high carrier mobility along the direction resulting in lower electrical resistivity than that of a single crystalline equivalent. The specimen also showed moderate carrier concentration, which led to a plausible Seebeck coefficient. Since the specimen exhibited the significantly low thermal conductivity with the electrical properties, it recorded a higher figure of merit than the equivalent, which is the highest thermoelectric performance for p-type WSe2 in bulk phase ever developed.

(Ta,Nb)C composites formed with graphene nanoplatelets by spark plasma sintering

TaC-NbC with the addition of sintering additive (5 vol.% B4C or 5 vol.% Si) and 3 vol.% Graphene Nanoplatelets (GNP) are consolidated by spark plasma sintering (SPS). GNP are aligned in a uniformly oriented direction perpendicular to the processing axis of the SPS equipment during consolidation. High load instrumented indentation is performed and the projected area of residual damage is compared to estimate relative fracture toughness. The projected residual damaged area after indentation in the surface direction (out-of-plane GNP orientation) was 89% greater in the TaC-NbC-5B4C-3GNP sample, and 96% greater in the TaC-NbC-5Si-3GNP sample when compared to indentation in the orthogonal (in-plane GNP orientation) direction. The toughening mechanisms prevalent in the orthogonal indentation direction (crack bridging and crack deflection) result in greater energy dissipation than the prevalent mechanisms in the surface indentation orientation (sheet sliding, crack bridging, and crack arrest).

Thermoelectric Properties of Mg2Si1-x-yGexSby Prepared by Spark Plasma Sintering

ABSTRACTThe magnesium compound Mg2Si and its solid solutions are expected asn-type thermoelectric (TE) material because they are non-toxic, have a large Clarke number, and are light weight. In this study, we improved TE performance by doping Ge into Sb-doped Mg2Si to cause phonon scattering and increase carrier concentration. A bulk of Sb-doped Si-Ge alloy as the raw material was fabricated using an arc-melting method. A high-purity Mg2Si was synthesized from metal Mg and Sb-doped Si-Ge alloy using spark plasma sintering equipment. For the samples with the same Sb concentration, the electrical conductivity was equivalent. On the other hand, the Seebeck coefficient was dependent on Ge concentration. Due to phonon scattering, thermal conductivity decreased by a small amount of Ge doping andκphdominated for thermal conduction. The minimum thermal conductivity of Mg2Si0.90Ge0.10was 2.25 W/mK (κph: 2.06 W/mK,κel: 0.19 W/mK). The dimensionless figure of merit (ZT) for the Mg2Si0.945Ge0.05Sb0.005sample was higher than that of the others due to reducing thermal conductivity and increasing carrier concentration. The maximumZTwas 0.47 at 713 K.

Microstructure and Mechanical Properties of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 Bulk Metallic Glass Compacts

In the present study, we report the relative density, microstructure and deformation behaviour of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 bulk metallic glass (BMG) compacts. The compacts were prepared by melt spinning of alloy to get amorphous ribbons followed by mechanical milling to obtain powder and then sintering using spark plasma sintering equipment at different processing temperatures and pressures. Higher sintering pressures and higher sintering temperatures within the supercooled liquid region were found to be beneficial for obtaining high relative densities in Fe-BMG. However, increasing the sintering temperature was found to result in crystallization. Amorphous compacts of 99.5 % relative density were successfully obtained through SPS of amorphous powders, using a pressure of 650 MPa, temperature of 520 °C and holding time of 5 min. The compaction in SPS was attributed to the deformation of the individual particles because of the high temperature and pressure. The fracture strength and strain of the compact with 99.5 % relative density during quasi static compression test was found to be 2.7 GPa and 0.1, respectively. An interrupted compression experiment revealed the formation of numerous shear bands.

Spark Plasma Welding of Austenitic Stainless Steel AISI 304L to Commercially Pure Titanium

In modern fast-breeder nuclear power plants, on-site fusion welding of austenitic stainless steel AISI 304L and commercially pure titanium pipes is called for. The application imposes stringent requirements on these joints in terms of tensile strength, bend ductility, and corrosion resistance in boiling nitric acid. However, fusion welding of stainless steel to titanium directly is a near impossibility because of inevitable brittle intermetallic formation between iron and titanium and, consequently, serious weld cracking problem. All things considered, the best way to realize these joints is to make use of solid-state welded stainless steel/titanium (SS/Ti) dissimilar pipe joining inserts or adaptors. Towards this end, many solid-state welding techniques such as diffusion bonding, friction welding, and explosive welding have been tried in past, but without much success. In the current study, solid-state welding of SS rods to Ti rods was attempted in spark plasma sintering equipment. The potential of this new process, termed spark plasma welding, for dissimilar metal welding are discussed.

Thermoelectric properties of synthesized Mg2Si0.95-xGe0.05Sbx by spark plasma sintering

AbstractMagnesium silicide (Mg2Si) has attracted much interest as an n-type thermoelectric material because it is eco-friendly, non-toxic, light, and relatively abundant compared with other thermoelectric materials. In this study, we tried to improve the thermoelectric performance by doping Sb and Ge in the Mg2Si, as well as further optimizing x in the carrier concentration to cause phonon scattering. A high purity Mg2Si was synthesized from metal Mg and Sb doped Si-Ge alloy by using spark plasma sintering (SPS) equipment. The sintered samples were cut and polished. They were evaluated by using X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses. The carrier concentration of the samples was measured by using Hall measurement equipment. The electrical conductivity and Seebeck coefficient were measured by using a standard four-probe method in a He atmosphere. The thermal conductivity was measured by using a laser-flash system. We succeeded in obtaining a Sb doped Mg2Si0.95Ge0.05 sintered body easily without any impurities with the SPS equipment. The electrical conductivity of the sample was increased, and thermal conductivity was decreased by increasing the amount of doped Sb. The dimensionless figure of merit ZT became 0.74 at 733 K in the Mg2Si0.95-xGe0.05Sbx sample with x = 0.0022.

Joining of 316L stainless steel by using spark plasma sintering method

Spark plasma sintering equipment was used to join 316L stainless steel rods with or without a powder interlayer. The powder layer with high electrical resistance was assumed to act as an effective local heat source. Resistance measurements of powders at room temperature showed that the resistance increased by orders of magnitude compared to the bulk material. The parameters influencing the joining process including current (heating power), heating time, pressure, pulse sequence, particle size and powder amount have been investigated. Results showed that especially by rightly adjusting current and heating time, high strength joint can be obtained. By applying only small pressure, deformation of the joint could be avoided. With a thicker powder interlayer, the distortion of the sample could be reduced, and powders with small particle size can produce higher strength samples. By adjusting all these parameters, samples with high strength can be obtained within seconds, so that the heat-affected zone can be markedly reduced.

Improvement of Electrical Contact Between TE Material and Ni Electrode Interfaces by Application of a Buffer Layer

A single π-structure thermoelectric (TE) module based on p-type NaCo2O4, n-type Mg2Si, and Ni electrode was fabricated by the spark plasma sintering (SPS) method. The NaCo2O4 powder was synthesized by using a metal–citric acid complex decomposition method. Bulk Mg2Si prepared by melt quenching was ground into a powder and sieved to particle size of 75 μm or less. To obtain a sintered body of NaCo2O4 or Mg2Si, the powder was sintered using SPS. Pressed Ni powder or mixed powder consisting of Ni and SrRuO3 powder was inserted between these materials and the Ni electrode in order to connect them, and electrical power was passed through the electrodes from the SPS equipment. The open-circuit voltage (VOC) values of a single module in which TE materials were connected to the Ni electrodes by using pressed Ni powder was 82.7 mV, and the maximum output current (Imax) and maximum output power (Pmax) were 212.4 mA and 6.65 mW at ΔT = 470 K, respectively. On the other hand, VOC of a single module in which TE materials and an Ni electrode were connected with a mixed powder (Ni:SrRuO3 = 6:4 volume fraction) was 109 mV, and Imax and Pmax were 4034 mA and 109 mW at ΔT = 500 K, respectively. These results indicate that the resistance at the interface between the TE materials and the Ni electrode can be decreased and the output power can be increased by application of a buffer layer consisting of Ni and SrRuO3.

Spark Plasma Sintering of Al6061 and Al2124 Alloys

Recently spark plasma sintering has been proven to be effective non-traditional powder metallurgy technique to sinter fully dense materials in short sintering times at relatively low sintering temperatures and without a binder or pre-compaction step. Despite the importance of aluminum based alloys as candidate materials for applications in aerospace and automotive industries because of their light weight, very little work was dedicated to spark plasma processing of these materials. In this work we explored the possibility to process Al2124 and Al6061 alloys using spark plasma sintering technique. The sample were sintered for 20 minutes at 400, 450 and 500°C using fully automated FCT system spark plasma sintering equipment. A scanning electron microscope was used to analyze the microstructure of sintered samples. The density and Vickers microhardness of the sintered samples were measured using an electronic densimeter and a digital microhardness tester respectively. The hardness and density of the spark plasma sintered samples were reported as a function of sintering temperature. It was found that full density (100 % of the theoretical density) was achieved with sintering for 20 minutes at 450°C for Al6061 alloy and at 500°C for Al2124 alloy. The density and microhardness of the sintered samples increased with the increase of sintering temperature.

High-Temperature Mechanical Spectroscopy of Nitrogen-Rich Ca-α-SiAlON Ceramics

Nitrogen-rich Ca–α-SiAlON ceramics made with different starting powder compositions have been studied by high-temperature mechanical spectroscopy in parallel with compressive deformation in a spark plasma sintering equipment. The mechanical loss spectra measured upon heating show a relaxation peak at about 1150 K and a high-temperature exponential background at higher temperatures (>1400 K), which are attributed to the α-relaxation in the glassy phase and to grain-boundary sliding, respectively. A theoretical interpretation of the results shows that the peak position is mainly a function of glass viscosity. The amplitude of the peak is not only affected by the glassy phase quantity but also depends on the restoring force due to grain elasticity. Therefore, despite a higher amount of glassy phase specimens containing elongated grains may show a lower peak. The amplitude of the internal friction peak corresponding to α-relaxation can be used to predict the compression creep of silicon-nitride-based ceramics.