Spark Plasma Sintering Furnace Research Articles

Synthesis of Ti3SiC2 Phases and Consolidation of MAX/SiC Composites-Microstructure and Mechanical Properties.

The article describes the Ti3SiC2 powder synthesis process. The influence of the molar ratio and two forms of carbon on the phase composition of the obtained powders was investigated. The synthesis was carried out using a spark plasma sintering (SPS) furnace. In addition, using the obtained powders, composites reinforced with SiC particles were produced. The obtained results showed no effect of the carbon form and a significant impact of annealing on the purity of the powders after synthesis. The composites were also consolidated using an SPS furnace at two temperatures of 1300 and 1400 °C. The tests showed low density and hardness for sinters from 1300 °C (maximum 3.97 g/cm3 and 447 HV5, respectively, for composite reinforced with 10% SiC). These parameters significantly increase for composites sintered at 1400 °C (maximum density 4.43 g/cm3 and hardness 1153 HV5, for Ti3AlC2-10% SiC). In addition, the crack propagation analysis showed mechanisms typical for granular materials and laminates.

Rapidly synthesizing Hf2SB ceramics by thermal explosion

Transition metal sulfides and their corresponding derivatives, such as MAX phases, have been widely studied because of their unique physical properties. However, due to the low melting/boiling point and volatile characteristics of sulfur, it is difficult to control the element ratio in their in-situ synthesis, and some impurities are introduced. Based on this, we first studied the reaction mechanism of sulfur-containing MAX phase Hf2SB. Previous studies generally believed that the mechanism of MAX phase synthesis is that elements M and X first form compounds and then react with elements A. Interestingly, Hf reacts with sulfur to form Hf2S firstly, and then boron enters the octahedral gap between the two layers of hafnium to form Hf2SB. Based on the reaction mechanism, Hf2SB with a purity of 91.99 wt% and its corresponding sulfide Hf2S with a purity of 96.75 wt% were successfully and rapidly synthesized by thermal explosion synthesis using a spark plasma sintering furnace. The microstructure of the sample fractured surface was observed by scanning electron microscopy, which confirmed that the Hf2SB grains were in lath shape, that is, the typical grain shape of MAX phases. The crystal structure and atomic positions of Hf2SB and Hf2S were obtained accurately, and the similar structure between them confirms our conclusion on the reaction mechanism.

Magnetic performance of SrFe12O19–Zn0.2Fe2.8O4 hybrid magnets prepared by spark plasma sintering

In the last few years, significant effort has again been devoted to ferrite-based permanent magnet research due to the so-called rare-earth crisis. In particular, a quest to enhance ferrites maximum energy product, BH max, is underway. Here, the influence of composition and sintering conditions on the microstructure and consequently magnetic properties of strontium ferrite-based hybrid composites was investigated. The powder mixtures consisted of hydrothermally synthesised Sr-ferrite with hexagonally shaped platelets with a diameter of 1 μm and thickness up to 90 nm, and a soft magnetic phase in various ratios. Powders were sintered using a spark plasma sintering furnace. The crystal structure, composition and microstructure of the starting powders and hybrid magnets were examined. Their magnetic properties were evaluated by vibrating sample magnetometer, permeameter and by single-point-detection measurements.

Tribological Properties of Spark Plasma Sintered Al-SiC Composites.

The paper presents the results of research on the tribological properties of spark-plasma-sintered Al-SiC composites. Composites with contents of 50 and 70 wt.% SiC were prepared. The sintering process was carried out using an HP D 25/3 spark plasma sintering furnace under vacuum, at the sintering temperature of 600 °C and compaction pressures of 50 and 80 MPa, respectively. The heating rate was 100 °C/min and the holding time was 10 min. Composites with a density of 91–100% were obtained. The tribological properties of the composites were evaluated based on weight loss and the coefficient of friction using a block-on-ring tribotester. Along with the weight percentage of SiC and compaction pressure, the sliding distance, and load during the tribological test were considered. Both the weight percentage of SiC and compaction pressure affected the tribological behavior of Al-SiC composites. It was found that the wear resistance was higher when a lower compaction pressure and a smaller amount of reinforcing phase (50 wt.%) were used.

Machining of TiB<sub>2</sub>- SiC Ceramic Composites through WEDM Process

In the present study Spark Plasma Sintering (SPS) technique is used to synthesis of particulate Ceramic Matrix Composites (CMCs). SPS is a type of hot pressing method and in this method, the rate of heating is from 100C to 1000C per minute with high densification. TiB2 (average size of 14 μm) particles were chosen as matrix and SiC (average size of 1 μm) particles were used as reinforcement. In the first stage of the study, synthesis of CMCs with TiB2 matrix and SiC reinforcement with varying volume% (0, 5, 10 and 15 vol.%) was carried out using Spark Plasma Sintering furnace available at IIT Madras in 1100°C, 40MPa and 10 min hold of time. But machining of CMCs from conventional machining processes is difficult especially to make complex and precise parts from CMCs. Hence, in the second stage of the work, Wire Electric Discharge Machining (WEDM) studies were carried out on the processed four composites by varying current (2, 3 and 4 A), Pulse on (Ton-30, 60 and 90 μs) and Pulse off time (Toff-5, 10 and 15 μs) as per Taguchi L9 orthogonal array. WEDM studies revealed that at 4A current, 60μs Ton and 5μs Toff gave maximum material removal rate (MRR) of 2.93 mm3/s, 2.27 mm3/s, 2.71 mm3/s and 0.62 mm3/s for CMC with 0% SiC, 5% SiC, 10% SiC, 15% SiC vol.% reinforcement respectively. To reduce material wastage during machining, kerf width is considered and in which 3A current, 90μs Ton and 5μs Toff gave the least kerf of 0.35 mm, 0.32 mm, 0.33 mm and 0.28 mm for 0% SiC, 5% SiC, 10% SiC, 15% SiC vol.% reinforcement respectively.

Microstructures and mechanical properties of TiAl alloy fabricated by spark plasma sintering

This work deals with the consolidation of a TiAl alloy powder by spark plasma sintering (SPS). Pre-alloyed powder with a composition of Ti–48Al–2Cr–2Nb (at.%) was consolidated in a SPS furnace at temperatures between 1200[Formula: see text]C and 1325[Formula: see text]C and with a pressure of 50 MPa. The microstructures obtained after SPS depend on the sintering temperature. Tensile tests at room temperature were performed. The alloy SPSed at temperatures not less than 1250[Formula: see text]C exhibits good properties at room temperature.

Face dependent footprints of carpet-like graphene films grown on polycrystalline silicon carbide

Continuous epitaxial graphene (EG) films have been grown on polished surfaces of dense polycrystalline SiC ceramics by heating in a Spark Plasma Sintering furnace (SPS). The confining of the sample into a graphite die and the use of a high pulsed dc current that triggers the joule heating of the system play a key role in the graphene formation by Si sublimation. The polycrystalline nature of the sample has allowed the comparison, through different local probe microscopies and micro-Raman spectroscopy, between EG films simultaneously grown on different SiC faces at exactly the same conditions, providing valuable information on their thickness, quality and stresses. Notably, whereas a graphene bilayer grows over Si-face grains, multilayer graphene (∼10 layers) forms on C-faces. The observed nano-electronic and nano-mechanical heterogeneities of the surface, showing up as differences in charge state and strain release mechanisms, are found to arise from the dependence of the EG properties when developed on each grain orientation; the same applies in the case of the macro-mechanical scratch resistance. SPS demonstrates to be a reliable and flexible methodology to prepare continuous graphene films on SiC components with many possibilities for scaling-up at low cost.

Pulsed electrodischarged pressure sintering and flash sintering, a review

Abstract Electric current activated/assisted sintering (ECAS) is a growing class of versatile techniques for sintering particulate materials. Nowadays, most of the scientific attention is focused on pulsed electric current sintering known as spark plasma sintering (SPS). SPS has been successfully applied to electrically conductive and low-electrical-conductivity ceramics although the measured temperature is not directly related to the sintering temperature. Here, we summarize the present status and problems of SPS technology, and introduce our approach to develop SPS. Then, as a future direction, we will demonstrate flash sintering using SPS furnace and conductive powders.

The effects of particle size distribution and sintering conditions on bending strength of sintered Ni-30%Fe alloys

This work reports effect of the powder grain size distributions on the bending strength sintered Ni-30%Fe alloys obtained from mixed coarse-fine micron size metal powders. Two dissimilar particle sizes of Ni and Fe metal powders were mixed by subjecting them to translational and rotational agitations using the T2F Turbula Shaker Mixer. The mixed powders were moulded using graphite dies and sintered in vacuum and at constant pressure using Spark Plasma Sintering furnace (HHPD-25). The ratios of the two metals were varied as well as the sintering temperature and time. The morphology and microstructures of both powders and sinters were studied using field emission scanning electron microscopy (JSM-7600F) equipped with energy dispersive X-ray spectrometer (EDS) facilities. The phases in the sintered specimens were characterized by X-ray diffraction (XRD). The densities of the samples were determined, The Vickers microhardness at room temperature and bending strength of the sintered alloy specimens were measured. Comparatively, low heating rate (50 oC/min) produced enhanced microstructures hence higher bonding, bending strength and densification than samples at high heating rate (150 oC/min).

ANFIS based model to forecast the Wire-EDM parameters for machining an Ultra High Temperature Ceramic composite

In this work, a ZrB2 based ceramic composites with 25 wt. % B4C sintered in spark plasma sintering furnace at 2000°C for 10 min under 50 MPa pressure has been machined with Wire electrical discharge machine (WEDM) and can readily be cut to intricate shapes to meet the requirements of industry. The adaptive neuro fuzzy inference systems (ANFIS) has been used to generate mapping relation between input parameters and output responses. ANFIS is a neuro fuzzy technique where the fusion is made between the neural network and the fuzzy inference system. Also the ANFIS models have been tested by a confirmative test and the results shows minimum root mean square error (RMSE) as 0.0416 for kerf width and 0.9605 for machining speed. This verification indicates that ANFIS modeling can be used to forecast the responses.

Dispersion and densification of nano Si–(Al)–C powder with amorphous/nanocrystalline bimodal microstructure

AbstractThe dispersion behavior and densification of nano Si–(Al)–C powder with amorphous/nanocrystalline bimodal microstructure were investigated. The Si–C powders synthesized by a mechanical alloying (MA) process had a near‐spherical shape with an average particle size of 170 nm. A solid loading of 62 vol% was achieved using polyethyleneimine (PEI) as a dispersant. The optimum dispersant amount was 1 wt% based on zeta potential, sedimentation, and viscosity analysis data. The high zeta potential value (73 mV) compared with that of the commercially available SiC (65 mV) was caused by modified surface properties and consequent promotion of the cationic dispersant adsorption. A Si–Al–C slurry containing 6.5 wt% of sintering additives with a solid loading of 60 vol% was also prepared. The relative density of the dried Si–Al–C slurry was 63.3% without additional compaction, which could be densified at 1650°C at a pressure of 20 MPa using a spark plasma sintering furnace.

Exploitation of Field-Assisted Sintering Technology (FAST) to Produce Pre-Forged Billets from Metastable Beta Titanium Alloy Powder

Powder produced by gas atomisation of metastable beta alloy Ti-5Al-5Mo-5V-3Cr has been consolidated using field-assisted sintering technology (FAST) to examine the suitability of the process to produce pre-forged billets as opposed to the conventional multi-step Kroll-VAR-forging route. FAST testing was performed using an FCT Systeme GmbH spark plasma sintering furnace type HP D 25 at The University of Sheffield. The dwell temperature was varied between 800 and 1200°C and the dwell time between 3 and 60 minutes. The process was found to allow very precise control over the beta grain size in Ti-5Al-5Mo-5V-3Cr by variation of the dwell time and dwell temperature, producing grain sizes between ~40 and ~350 μm. However, it was found that the grain size was increased more by increasing the dwell temperature than increasing the dwell time. The porosity was found to be between 99.5 and 100 % for all dwell temperatures at dwell times of 30 minutes or above. FAST has the ability to produce almost fully consolidated Ti-5Al-5Mo-5V-3Cr pre-forged material from powder with a controlled beta grain size, which is not possible by other methods.

Influence of Carbon Nanotube Dispersion in UO2–Carbon Nanotube Ceramic Matrix Composites Utilizing Spark Plasma Sintering

A novel uranium dioxide (UO2)–carbon nanotube (CNT) ceramic matrix composite fuel concept has been proposed for a nuclear fuel with increased thermal conductivity. Investigations were performed to analyze the dispersion of CNTs in a UO2 matrix utilizing homogenization and sonication techniques. Ethanol and ortho-dichlorobenzene (ODCB) were utilized as solvents during the mixing process. Distributions of both multiwalled carbon nanotubes and single-walled carbon nanotubes (SWNTs) were analyzed. It has been determined that CNTs can be homogeneously distributed into a UO2 matrix using mechanical processes, sonication, and homogenization in the organic solvent ODCB. The powder mixture of UO2 and CNTs was sintered at 1300°C with a hold time of 5 min and 40-MPa pressure in a spark plasma sintering furnace, and the resulting grain size distribution was analyzed. It was observed that where the distribution of CNTs was not well controlled, significant grain growth of UO2 occurred. However, where the CNT distribution is well controlled, the grain growth is limited by the pinning effect of the CNTs along the grain boundaries. The resulting pellet thermal conductivity was improved by 29.7% with the addition of 5 vol % SWNT, relative to pure UO2 values. Raman spectroscopy in conjunction with scanning electron microscopy shows that most CNTs survive both the mixing and sintering processes.

Influence of coated SiC particulates on the mechanical and magnetic behaviour of Fe–Co alloy composites

Near-equiatomic Fe–Co alloy composites containing 0, 5 and 10 vol% of uncoated and coated SiC particles were prepared by applying a uniaxial pressure of 80 MPa at 900 °C for 5 min in a spark plasma sintering furnace. The SiC particles used in this study were coarse, with an average particle size of 20 μm and their surfaces were coated with four different types of coatings, namely Ni–P, Cu, Co and duplex Cu and Ni–P by an electroless plating method. Quasi D.C. magnetic, bending and hardness tests were performed on the composites. The influence of particulate coatings on the magnetic and mechanical behaviour of the composites was investigated by correlating their properties with their microstructures as observed using scanning electron microscopy and optical microscopy and crystallographic information as obtained using X-ray diffraction. The cobalt coated particles were found to exhibit the best wettability with the matrix without the formation of deleterious intermetallic compounds at the interface. Because of the better interfacial bonding in the composites with Co coated particles, there was an enhancement in flexural strength and permeability compared to the uncoated and other coated particulate composites studied. In addition, inclusion of cobalt coated SiC particulates produced an increase in hardness and a decrease in coercivity compared to the monolithic material.

Mechanical and magnetic characterisation of SiC whisker reinforced Fe–Co alloy composites

SiC whisker reinforced Fe–Co composites containing up to 3vol% of bare, copper, Ni–P and cobalt plated whiskers were prepared in a spark plasma sintering furnace at 900°C, applying a pressure of 80MPa for 5min. The influences of the bare and the coated whisker additions on the magnetic and mechanical properties of the brittle matrix were assessed and correlated using their microstructural and fractographic observations. The bare whiskers played dual and contradicting roles on the grain growth behaviour of Fe–Co. The insulating fibres, which promoted grain growth of Fe–Co by concentrating the sintering current in the regions away from them, reduced the grain growth kinetics by pinning the boundaries. The grain growth was more pronounced in all the materials with more than 2vol% of whiskers. Among the coatings investigated, the amorphous Ni–P coating aided to achieve maximum improvements in both strength and ductility by forming nanocrystalline intermetallic compounds with Fe–Co and by promoting dispersion of the whiskers in the matrix alloy. The copper and cobalt coatings were not beneficial in improving the mechanical properties of the composites because of their inability to promote homogeneous dispersion of the whiskers and to form new intermetallic compounds with the matrix alloy, respectively.

Phase stability and rapid consolidation of hydroxyapatite–zirconia nano-coprecipitates made using continuous hydrothermal flow synthesis

A rapid and continuous hydrothermal route for the synthesis of nano-sized hydroxyapatite rods co-precipitated with calcium-doped zirconia nanoparticles using a superheated water flow at 450°C and 24.1 MPa as a crystallizing medium is described. Hydroxyapatite and calcium-doped zirconia phases in the powder mixtures could be clearly identified based on particle size and morphology under transmission electron microscopy. Retention of a nanostructure after sintering is crucial to load-bearing applications of hydroxyapatite-based ceramics. Therefore, rapid consolidation of the co-precipitates was investigated using a spark plasma sintering furnace under a range of processing conditions. Samples nominally containing 5 and 10 wt% calcium-doped zirconia and hydroxyapatite made with Ca:P solution molar ratio 2.5 showed excellent thermal stability (investigated using in situ variable temperature X-ray diffraction) and were sintered via spark plasma sintering to >96% sintered densities at 1000°C resulting in hydroxyapatite and calcium-doped zirconia as the only two phases. Mechanical tests of spark plasma sintering sintered samples (containing 10 wt% calcium-doped zirconia) revealed a three-pt flexural strength of 107.7 MPa and Weibull modulus of 9.9. The complementary nature of the spark plasma sintering technique and continuous hydrothermal flow synthesis (which results in retention of a nanostructure even after sintering at elevated temperatures) was hence showcased.

Spark Plasma Joining of ZrB2–SiC Composites Using Zirconium–Boron Reactive Filler Layers

Spark plasma joining is used to join ZrB2–SiC composites with seamless microstructures at the joint that results in retention of high‐temperature mechanical and oxidation properties after joining. Our approach uses a spark plasma sintering furnace and Zr–B powder filler layers to join the parts together. The joining processing parameters used to optimize the joint microstructure were filler composition, target temperature, hold time, and volume of filler. A filler of 1 mm3 and spark plasma joining conditions at 1800°C for 300 s resulted in the formation of a joint region that was indistinguishable from the bulk substrates. Room and high‐temperature (1350°C) shear strengths of joined substrates measured equal to baseline substrates and oxidation behavior for joined and baseline substrates were equivalent after static air oxidation at 1700°C. X‐Ray diffraction measurements show the joint is composed of ZrB2 and ZrC. We found the joining mechanism to be solid‐state bonding of ZrB2 that formed from the Zr–B filler and reaction bonding by the formation of ZrC. Spark plasma joining rapidly joins ZrB2–SiC and probably other conductive ultra high‐temperature ceramic composites, and has the potential to impact the rapid assembly and joining of complex thermal protection material systems.

The Phase Evolution of the TiC Cermet Fabricated by Spark Plasma Sintering

The TiC cermet widly used for high hardness working dies and tool materials was fabricated by carbo-thermic reduction of thtania-precusor or self-propergating high temperature synthesis(SHS) reaction. In this paper, the titanium hydride, carbon and iron alloy(D'AE) powders which were mixed for uniform microstructure by spex mill was sintered directly in the spark plasma sintering(SPS) furnace. The nano TiC powders which were fabricated by mechanical alloying using TiH 2 powders mixed with carbon powder were sintered also in the SPS furnace. The effects of mechanical alloying time and sintering procedure on the phase changes of sintered microstructure were evaluated with X-ray diffraction, electron microscopy, EDS, and hardness tester. As-milled powders for 5 hours were successfully synthesized to the TiC phase of 300nm mean particle size. The microstructure of spark plasma sinterd TiC/Fe cermet using TiC powders fabricated by 5 hours milling shows lower density in compare with the spark plasma sintered cermet using mixed powders. The nano size TiC particles were formed homogeneously during spark plasma sintering by the selfpropergating synthesis reaction.

Enhanced densification of pure SnO2 by spark plasma sintering

Densification of pure SnO2 by conventional sintering is known [1, 2] to be very difficult due to the evaporative decomposition of SnO2 into SnO(g) and 1/2O2(g) occurring during sintering. The adsorbed impurities on the surface were also suggested to retard the densification process [3]. Therefore, it has been reported [4] that the fully-dense SnO2 specimens could be obtained only by hot isostatic pressing. In this investigation, we tried to achieve a full densification of SnO2 specimen by spark plasma sintering (SPS) which is known to be quite effective for the densification of various materials [5–10]. Although the exact mechanism of the enhanced densification by SPS has not been clarified yet, the surface cleaning by joule heating due to dielectric breakdown [5] would remove the surface impurities. Note also that the SPS is usually carried out at lowtemperatures compared with the conventional sintering, so that the evaporation of SnO2 can be minimized. In this study, therefore, the densification of SnO2 specimens using SPS process was investigated by varying the SPS conditions and starting powders. Commercial SnO2 powders (99.9% purity, Aldrich Chemicals, USA) as well as the powders prepared in the laboratory were used. To prepare the SnO2 powders, 200 ml of 0.2 M SnCl4·5H2O (99.9% purity, Aldrich Chemicals) butanol solution was dripped into 400 ml of 0.5 M (C2H5)2NH (diethylamine, 99.9%, J. T. Baker Co.) butanol solution. Ten milliliters of water was additionally dripped into solution for promoting hydrolysis reaction. The precipitate was washed using ethanol until no Cl− ion was detected. After pulverization, the powders were heat-treated at 250 ◦C for 1 hr to decompose residual (C2H5)2NH, and calcined at 500◦C for 1 hr. A key feature to be noted in the powder processing used in this study is the minimization of water consumption to enhance the dispersion of the powders [11]. Transmission electron microscope (TEM, JEM3000F, JEOL, Japan) was used to observe the agglomerates and particle sizes of each powder. For sintering, the powders were placed in a graphite die (10 mm in diameter) and heat-treated at various temperatures for 5 min under vacuum (∼2.7 Pa) in SPS furnace (Spark Plasma Sintering, ElTek Co., Korea). The pressure and electric current applied during sintering were 37.5 MPa and 1200 A, respectively. The densities