Effect Of Spark Plasma Sintering Research Articles

Effects of spark plasma sintering and the nanodiamond amount on titanium-nanodiamond composite properties

Titanium/nanodiamond (ND) mixtures were sintered using spark plasma sintering (SPS). Densification was studied for Ti + x wt% ND mixtures (where x = 2, 5, 10 and 15) to determine the optimized cycles. Ti/ND mixtures were then sintered under these optimized conditions achieving relative densities higher than 96 %. The SPS temperatures for the Ti + 2 wt% ND, Ti + 5 wt% ND, Ti + 10 wt% ND and Ti + 15 wt% ND mixtures were 1000 °C, 1050 °C, 1150 °C and 1150 °C, respectively. Numerical simulation by finite elements were used to check the thermal homogeneity in the sample and to determine the maximal temperature in the sample to ensure avoiding graphitization. The effects of ND on the Ti/ND mixtures were investigated. Microstructural characterizations reveal the presence of three different phases including a Ti phase, a non-stoichiometric TiCx solid phase and NDs located inside the TiCx grains. Indeed, NDs react with Ti to form the TiCx solid phase. However, a fast sintering with temperature below graphitization of diamond allows to keep nanodiamond structure into the Ti/ND mixtures. Hardness and electrical conductivity of the Ti/ND mixtures were measured. The results show that the higher the ND content, the more the hardness of the composite increases and the more the electrical conductivity decreases. Hardness increased from 340 HV to 1346 HV for Ti and the Ti + 15 wt% ND mixture, respectively. Electrical conductivity is reduced by a factor of three for the Ti + 15 wt% ND mixture relative to Ti which can be explained by the microstructure exhibiting fewer Ti grains in favor of the TiCx solid phase when ND content was increased in the composite.

Effect of spark plasma sintering on the dielectric response of Sm and La co-doped barium titanate

Samarium and Lanthanum co – doped barium titanate ceramic (Ba0.96Sm0.02La0.02TiO3) was synthesized by an ethylene glycol polymerization route followed by both conventional and spark plasma sintering. A small amount of grain growth was observed after the spark plasma sintering, which could be due to the high heating rate during the process which causes agglomeration. The spark plasma sintered ceramic showed a significant increase in room temperature relative permittivity value from 247.76 to 4129.355 respectively at 1 kHz respectively. Temperature dependent permittivity showed a shift in curie temperature to 393 K for the SPS ceramic.

Enhanced Energy Storage Properties of La-Doped Sr0.6Ba0.4Nb2O6 Relaxor Ferroelectric Ceramics Prepared by Spark Plasma Sintering.

In this work, La-doped Sr0.6Ba0.4Nb2O6 ferroelectric ceramics were fabricated by the conventional solid state reaction method (CS) and spark plasma sintering (SPS), respectively. The microstructure, phase structure, dielectric properties, relaxor behavior, ferroelectric and energy storage properties were investigated and compared to indicate the effects of spark plasma sintering on their performances. The results show that the grain shape changes from columnar to isometric crystal and the grain size decreases obviously after spark plasma sintering. The dielectric constant of the CS sample and the SPS sample both show a typical relaxor behavior with obvious frequency dispersion. The diffusion parameters (γ) of both CS sample and SPS sample are close to 2 and all the samples present slim polarization–electric (P-E) loops, which verify the relaxor behavior. Moreover, the breakdown strength, Eb, and discharge energy storage density, Wrec, of La-doped Sr0.6Ba0.4Nb2O6 ferroelectric ceramics prepared by SPS are improved significantly. This work provides guidance for improving the energy storage performance of ferroelectric ceramics with tungsten bronze structures by decreasing the grain size through adopting a different sintering method.

Effect of spark plasma sintering on microstructure and mechanical properties of AA7075/B4C/ZrC hybrid nanocomposite fabricated by powder metallurgy techniques

In the present work, AA7075/B4C/ZrC hybrid nanocomposite has been fabricated by spark plasma sintering (SPS) process at a temperature of 500 °C with a heating rate of 50 °C/min for a period of 5 min. Microstructures and crystal phase structures have been investigated by scanning electron microscopy and X-ray diffraction techniques, respectively. It is observed from the results that the strong and clean interfaces along with uniform distribution of reinforcement particles are present in the SPS-synthesized composites, while the conventionally sintered composites possessed microporous structures. Mechanical properties of the SPS composite are found to be superior as compared to the conventional-sintered composites, where the high tensile and compression strengths of 605 and 712 MPa, respectively, are noted for SPS composite, while it is 502 and 598 MPa, respectively for the conventional-sintered composites. These observed enhanced properties could be attributed to the unique features of the SPS process, such as limited grain growth, clean interface bond formed via the breakage of oxide layers on particle surfaces due to spark discharges, and enhanced diffusion phenomenon that made the interfaces of the composite to be stronger.

Effect of spark plasma sintering and reinforcements on the formation of ultra-fine and nanograins in AA2024-TiB2-Y hybrid composites

This study reports the influence of sintering mechanism and reinforcement materials on the formation of ultra-fine and nanograins in Al-TiB2-Y nanohybrid composites. The mechanical properties of the composites and their corresponding micro and nanostructures are correlated. The experimental and characterization results revealed that despite the addition of TiB2, the hard and brittle Al3Ti phase formation in the composites was suppressed and hence, their ductility was retained. It was found that yttrium content of 0.3 ​wt% was the optimum amount which created advantageous spark plasma sintering conditions, and the addition of 0.3 ​wt% promoted the formation of bi-modal size grains (ultra-fine and nano) along with micro grains, Ω and other nano precipitates, resulting in a significant enhancement in the composite properties. The formation of ultra-fine and nanograins may be attributed to the combined effect of melting and rapid solidification at necking zones due to Joule's heating and thermo-mechanical fatigue. Among all the sintered composites, the highest hardness (137 HV), ultimate tensile strength (UTS) (496 ​MPa), yield strength (YS) (438 ​MPa) with 15.7% elongation were obtained in the sintered sample reinforced with 1.0 ​wt% TiB2 and 0.3 ​wt% yttrium.

Issues and opportunities from Peltier effect in functionally-graded colusites: From SPS temperature modeling to enhanced thermoelectric performances

The quaternary sulphide V-Sn colusite, Cu26V2Sn6S32, is one of the most promising cost-efficient thermoelectric materials to date because of the low toxicity, wide availability and low cost of the composing elements. Recent studies have demonstrated the potential of this environmentally-friendly material and its transport properties are now well understood. In the present work, we take the next step of producing large quantities of optimised V-Sn colusite using industrial-grade precursors and investigating the effect of Spark Plasma Sintering (SPS) in the production of large cylindrical pucks of up to 30 mm in diameter and 10 mm in thickness. In the process, we identified and solved several key issues including the generation of temperature gradients during SPS, porosity and defect formation. The generation of radial and axial temperature gradients within the sample during SPS has been modeled using modified Fourier and Ohm laws and confirmed experimentally thanks to the TSPS-dependent transport properties of V-Sn colusite and EDS analysis. We demonstrate that large pucks of colusite with enhanced thermoelectric properties can be produced using a combination of SPS and High-temperature Isostatic Press (HIP). Overall, our work experimentally and theoretically demonstrates that the production of both homogeneous and functionally-graded bulk materials can be easily up-scaled through a careful control of the SPS conditions.

Effects of spark plasma sintering on enhancing the thermoelectric performance of Hf–Ti doped VFeSb half-Heusler alloys

This work presents a study on the thermoelectric properties of ultrafine grained Hf–Ti dual-doped VFeSb half-Heusler (HH) alloys treated by spark plasma sintering (SPS) at different temperatures. The concerned alloys were successfully synthesized by arc/induction melting and mechanical alloying (MA). Thermoelectric (TE) properties of Fe(V0.8Hf0.2)1-xTixSb (x = 0.0, 0.2, 0.4) HH samples were studied over the temperature range from 100 to 900 K. Hf and Ti as heavy elements were used as dopants to create point defects aiming to reduce the material's thermal conductivity by enhancing the phonon scattering. Since the transport properties of HH alloys are sensitive to heat treatment, the effect of sintering temperature is studied as well. It was found that the power factor is significantly improved by increasing the sintering temperature. As a result, the figure of merit was enhanced by ~10% for the Fe(V0.8Hf0.2)0.8Ti0.2Sb sample and by ~30% for the Fe(V0.8Hf0.2)0.6Ti0.4Sb sample which were sintered at 1123 K, compared to those sintered at 1023 K. The maximum value was recorded at 0.33 for the sample Fe(V0.8Hf0.2)Sb. This value is higher than that of the singly doped FeV0.9Hf0.1Sb sample with a maximum zT value of 0.08. Also, it is higher than the reported value of the FeVSb doped with Ti which shows maximum ZT of 0.174 calculated for FeV0.7Ti0.3Sb at 658 K.

Effect of Spark Plasma Sintering (SPS) at Temperatures of 900 and 950oc for 5 Minutes on Microstructural Formation of Fe-25Ni-17Cr Austenitic Stainless Steel

Effect of Spark Plasma Sintering (SPS) at Temperatures of 900 and 950oc for 5 Minutes on Microstructural Formation of Fe-25Ni-17Cr Austenitic Stainless Steel

Study of the potential effect of spark plasma sintering on the preparation of complex FGM/laminated WC-based cermet

In the present work, the capability of SPS process for the production of a complex composite possessing different forms of materials based on WC-Ni-Ti-CNT FGM/laminated composite is investigated. With regard to the unique properties of SPS in producing and densifying a large number of materials, a complex material was prepared as a sandwich structure based on the reaction among Ti, CNT, Ni and WC in various forms consisting of powders, sheets and nano-tubes. The starting materials were initially placed in the graphite mold in the order of Ni powders, WC-10Ni, CNTs coated Ti sheet, WC-15Ni and Ti sheet from bottom to top. The microstructure study showed that the layer of Ni powders was adequately densified as an integrated layer, the second layer, WC-Ni, was attached to the Ni layer from the bottom and, at the top, it was connected to the highly concentrated WC layer formed as a consequence of Ni consumed by Ti to form NiTi and Ni3Ti compounds. Moreover, the Ti sheets were changed into TiC particles as a result of reaction with WC and CNTs, and the WC-15Ni was placed at the top of this layer by bonding the structure properly; and eventually, the Ti sheet remained at the top of the specimen. The micro-hardness examination of the sample revealed the highest hardness related to the position of Ti-based layer due to the formation of intermetallic compounds and carbides.

Thermal–Mechanical Working of Spark Plasma Sintered Preforms Fabricated from Aluminum 2219 Powder

The effects of spark plasma sintering (SPS) coupled with hot upset forging of aluminum 2219 powder were studied. SPS was found to be an effective means of consolidating the powder as select specimens achieved full theoretical density. Although these as-sintered products also demonstrated a reasonable combination of tensile properties, they were greatly improved after forging. The most acute gains were observed in tensile ductility wherein three to four times improvements transpired. TEM analyses confirmed that forging manifested an appreciable disruption of the residual oxide networks present in the as-sintered product which was believed to be the primary driver of tensile property enhancements. SPS + forge products were also responsive to T87 heat treatment. Typical T87 values for tensile yield strength, UTS, and elongation to fracture were 350 MPa, 465 MPa, and 10 pct, respectively. Interestingly, these values were attainable over a wide range of sintering and forging temperatures. TEM analyses confirmed that θ′ was the dominant precipitate present in the SPS + forge-T87 products.

Effect of Zn and Co doping on antibacterial efficacy and cytocompatibility of spark plasma sintered hydroxyapatite

AbstractHydroxyapatite [Hap, Ca10(PO4)6(OH)2] is one of the most preferred bioceramic material for orthopedic implants and coatings due to its stoichiometric similarities with human hard tissues. However, foreign body implantation inside human body sometimes leads to bacterial film formation over the implant surface causing the implant failure, thereby needing a revision surgery. This study attempts to select the better dopant between zinc (Zn) and cobalt (Co) as per the antibacterial efficacy when doped in Hap. To prepare antibacterial transition‐metal‐doped Hap, Zn and Co are doped in Hap as per the chemical formula Ca10−x Mx(PO4)6(OH)2, (M = Zn or Co and x = 0.24) to improve antibacterial efficacy. Phase and microstructural characterization by Rietveld refinement, scanning electron microscopy (SEM), and Fourier transformation infrared spectroscopy (FT‐IR) confirms the doping. Evaluation of antibacterial activity against E coli reveals that both Zn‐ and Co‐doped Hap shows antibacterial property with the latter being more effective (zone of inhibition ~3 mm more) for the same level of doping. Inductively coupled plasma‐mass spectrometry confirms the presence of ~676 ppb Co+2 and ~303 ppb Zn+2 after leaching. In addition, cytotoxicity assay with NIH3T3 cell line reveals cytocompatibility of both the compositions with either dopant. The effect of spark plasma sintering on densification and mechanical properties of Co‐doped Hap is investigated for the first time and compared with Hap with the same level of Zn doping. It appears that Co‐doped Hap attains higher densification (~7% more) and fracture toughness (~2 times better) as compared to that of Zn‐doped counterpart (densification: 86% and fracture toughness: 0.75 ± 0.12 MPa √m). Thus, this study suggests that Co‐ and Zn‐doped Hap are promising candidates for bone tissue engineering with improved antibacterial properties and in addition, Co‐doped Hap can attain higher density and offer better fracture toughness than that of Hap doped with Zn.

Effect of Spark Plasma Sintering Current and Voltage on the Microstructure and Electrical Properties of Borosilicate Glass–Indium Tin Oxide Composites

Borosilicate glass–indium tin oxide (ITO) composites made from glass microspheres and ITO nanoparticles provide a unique model system to monitor the effect of spark plasma sintering (SPS) parameters on the resultant electrical properties of the composites. Composite sets containing different ITO content (up to 10 phr), fabricated under the same SPS conditions, are used as the starting point for the equivalent circuit analysis. The effect of changing the various SPS parameters such as heating rate, hold temperature, and applied pressure on the current and voltage profiles experienced by samples containing 2.5 phr (2.44 wt%) ITO, and their resultant electrical response are reported. Experiments are carried out varying a single SPS parameter at a time while keeping others constant. The applied pressures used range from 5 to 40 MPa; the hold temperature is varied from 610 to 680 °C; and the heating rate is tested between 2 and 200 °C min−1. It is demonstrated that not only do the current and voltage profiles change in all of these instances but also the microstructure and resultant electrical properties of the composite samples being fabricated. Results indicate that all of these parameters are interdependent and can affect the electrical properties of the fabricated samples by many orders of magnitude in some cases.

Effect of Spark Plasma Sintering on the Composition, Structure, and Conductivity of Nitrogen-Doped Carbon Nanotubes Modified by Cobalt Nanoparticles

New composites based on nitrogen-doped carbon nanoparticles (N-CNT), the surfaces of which are coated with metallic cobalt nanoparticles, are obtained via spark plasma sintering (SPS). Their morphology, microstructure, phase composition, and electric conductivity are examined thoroughly. The compacting of Co-modified nanotubes under specified SPS conditions is shown to help retain nitrogen atoms in the carbon structure and substantially raise the conductivity of the initial material, from 450 S/m for N-CNT to ∼4000 S/m in the sintered samples.

Effect of spark plasma sintering and high-pressure torsion on the microstructural and mechanical properties of a Cu–SiC composite

This investigation examines the problem of homogenization in metal matrix composites (MMCs) and the methods of increasing their strength using severe plastic deformation (SPD). In this research MMCs of pure copper and silicon carbide were synthesized by spark plasma sintering (SPS) and then further processed via high-pressure torsion (HPT). The microstructures in the sintered and in the deformed materials were investigated using Scanning Electron Microscopy (SEM) and Scanning Transmission Electron Microscopy (STEM). The mechanical properties were evaluated in microhardness tests and in tensile testing. The thermal conductivity of the composites was measured with the use of a laser pulse technique. Microstructural analysis revealed that HPT processing leads to an improved densification of the SPS-produced composites with significant grain refinement in the copper matrix and with fragmentation of the SiC particles and their homogeneous distribution in the copper matrix. The HPT processing of Cu and the Cu–SiC samples enhanced their mechanical properties at the expense of limiting their plasticity. Processing by HPT also had a major influence on the thermal conductivity of materials. It is demonstrated that the deformed samples exhibit higher thermal conductivity than the initial coarse-grained samples.

Multiferroic properties of nanostructured BiFeO3 tailored by milling and sintering by SPS

We report the magnetic and dielectric behavior of multiferroic bismuth ferrites synthesized using milling-annealing processes and tailored through the crystallite size reduction and the microstrain generated by mechanical milling. For synthesis, stoichiometric mixtures of Bi2O3 and Fe2O3 were mixed and milled for 5 h using a ball to powder weight ratio of 10:1 by high-energy ball milling and annealed at 650 °C. Subsequently, was carried out the Crystallite Size Reduction by Milling-Process at different milling times, in a range of 0–60 min, using a ball to powder weight ratio of 50:1 adding 5% wt. of methanol. X-ray diffraction and Rietveld analysis were used to evaluate the crystallite size and microstrain of the crystal structure. Morphology was studied by scanning electron microscopy, and magnetic behavior was evaluated using vibrating sample magnetometry. The powders obtained from Crystal Size Reduction by Milling-Process were sintered using spark plasma sintering in a 10 mm diameter graphite die at 750 °C. The effect of spark plasma sintering was evaluated by X-ray diffraction, Rietveld analysis, vibrating sample magnetometry and broadband dielectric spectroscopy. The results show a transformation from BiFeO3 phase to Bi2Fe4O9 phase for longest Crystallite Size Reduction by Milling Process time. Relationships between microstructural transformation and oxidation-reduction reactions, as well as antiferromagnetic-ferromagnetic changes, are discussed. Dielectric properties were found to decrease with high Crystallite Size Reduction by Milling-Process. Also, an unusual ratio was observed in magnetodielectric coupling which increases with Crystallite Size Reduction by Milling-Process time.

An investigation into the microstructure and mechanical properties of V4AlC3 MAX phase prepared by spark plasma sintering

The present work investigated the effect of spark plasma sintering of V4AlC3 MAX Phase on the microstructure and mechanical properties. Accordingly, Vanadium, Aluminum and carbon-black powders were mixed through a high energy mixer mill for 10 min in an ethanol medium. The direct inserted mixture of Al-V-C systems in a graphite mold was spark plasma sintered at 1350 °C with the initial and final applied pressure of 10 and 30 MPa at the vacuum condition of 20 Pa. The XRD investigations demonstrated the V4AlC3 crystalline phase along VC and Al2O3 as the side-effect reaction products. The microstructure analyses further indicated a perfect lath-like MAX phase with an almost proper growth. The FESEM micrographs of the prepared sample also indicated the formation of the V4AlC3 MAX phase with the lath-like shape. The fracture surface of the specimen also displayed deformed and separate lath-like phases as a result of the bending test. The different loads used for the hardness test demonstrated a deformation zone around the mark indentation. By increasing the applied load in the hardness test, the deformed area was enhanced. The prepared FESEM images from the deformed area showed different crack propagation mechanisms such as separation and branching, deflection, bridging, particles pulling out and breaking. 389 ± 19 MPa of bending strength and 6.74 ± 0.12 GPa of Vickers hardness were obtained for the prepared sample along the almost full densification as 99% of theoretical density.

Effect of spark plasma sintering on microstructure and electrical properties of ZnO-based varistors

Conditions for the elaboration of varistors by spark plasma sintering (SPS) are investigated, using 70 nm zinc oxide nano-particles. For this purpose, the system constituted of zinc oxide, bismuth oxide and other metal oxide is used. Material sintering has been performed by SPS at various temperatures and dwell times. Determination of the microstructure and chemical composition of the as-prepared ceramics are characterized by scanning electron microscopy and X-ray diffraction analysis. Micro-structural analysis revealed the presence of ZnO, spinel and bismuth rich phases. ZnO based Varistor samples sintered within climb speeds 100 and 400 °C/min are compared. The nonlinear electrical characteristics, current–voltage, are measured. The breakdown voltage of the varistors strongly depends on grain sizes. The results show that the best varistors are obtained by SPS at sintering temperatures ranging from 900 to 1200 °C.

Effect of Spark Plasma Sintering on the Structure and Compressive Strength of Porous Nickel

The effect of the temperature and time of spark plasma sintering (SPS) of a nickel powder on the structure of obtained samples of porous nickel was studied, and their mechanical strength under compression was evaluated. Based on the results of the experiments, it was found that spark plasma sintering the nickel powder at a temperature of 480°C with a holding time of 4 minutes enables to obtain samples with a porosity of 78.8%, having a structural performance and a compressive strength exceeding 1 MPa.

Improved Conductivity of Spark Plasma Sintered Ho-Substituted BaZrO3 Electrolyte Ceramics for IT-SOFCs

The effect of spark plasma sintering (SPS) on Ho-substituted BaZrO3 electrolyte ceramics was investigated to enhance the electrical conductivity for intermediate temperature solid oxide fuel cells (IT-SOFCs). The cubic crystal system with Pm3m space group symmetry, unit cell parameters, and bond length were revealed through the Rietveld refined X-ray diffraction (XRD) pattern. The microstructure of BaZr0.9Ho0.1O3−δ (BZH10) and BaZr0.8Ho0.2O3−δ (BZH20) SPS samples was found to be highly dense and exhibits the mixed inter/trans granular fracture mode through FESEM analysis. The average grain size and relative density of SPS at 1600 °C for 20 min of Ho-substituted BaZrO3 ceramics were found to decrease with the increase of Ho-substitution in BaZrO3 ceramics. The electrical impedance spectroscopic (EIS) analysis was performed under air and 3% humidified O2 atmosphere as a function of probing temperature from 250 to 800 °C. Thus, the total electrical conductivity of SPS BZH20 sample was estimated to be 4.91 ×...

Effects of spark plasma sintering temperature on densification, hardness and thermal conductivity of titanium carbide

The effects of spark plasma sintering (SPS) temperature on densification, microstructure, hardness and thermal conductivity of monolithic TiC ceramics were studied. Three samples were spark plasma sintered at temperatures of 1800, 1900 and 2000 °C for holding time of 7 min under pressure of 40 MPa. The relative density, hardness and thermal conductivity increased with sintering temperature from 1800° to 1900°C, but the mentioned properties decreased by spark plasma sintering at 2000 °C. The microstructural analyses showed that a fully-sintered TiC ceramic can be achieved at the SPS temperature of 1900 °C, with no significant growth of grains. The relative density, Vickers hardness and thermal conductivity of the TiC ceramic, sintered at the optimal temperature of 1900 °C, reached 99.4%, 25.7 GPa and 17.9 W/mK, respectively.