Spark Plasma Sintering Process Parameters Research Articles

Utilizing response surface methodology for the microstructural examination of CeO2/GNP composite coating applied via air plasma spraying and post-treated with spark plasma sintering

CeO2/GNP coatings were fabricated using a three-step process: high-energy ball milling, spray-drying, and air plasma spray (APS) deposition. Spark plasma sintering (SPS) was employed for post-treatment to densify the coatings. Response surface methodology (RSM) was employed to optimize SPS processing parameters, including temperature, pressure, and holding time, for minimizing porosity. A quadratic model was developed and validated using analysis of variance (ANOVA) to determine the influence of the independent variables. A regression equation was derived to predict porosity based on the process parameters. Scanning elctron microscopy(SEM) measurements revealed a significant 16 % porosity reduction in the densified coating. Interlamellar cracks and microcracks were significantly reduced, improving coating integrity and interface bonding. Enhancement of SPS parameters indicated that higher temperature and pressure combined with shorter holding times yielded minimal porosity. The study demonstrated that higher pressures exhibited a stronger impact on porosity at higher temperatures, while the effect of temperature was more pronounced at a holding time of 4 min. The interaction between pressure and holding time highlighted the importance of considering both parameters for effective porosity control in SPS. The constraints for each parameter have been defined through the optimization process. The set temperature is 950 °C, the pressure is established at 30 MPA, and the duration of the holding time is 4 min.

Process parametric optimization of spark plasma sintered Ni–Cr–ZrO2 composites using response surface methodology (RSM)

Materials properties are highly dependent on the processing parameters and technique used during sintering. The effect of Spark Plasma sintering process parameters (pressure and temperature) on the hardness and relative density of Ni–20Cr–5ZrO2 composite was investigated. Response Surface Methodology (RSM) from the design of experiment (DOE) technique was successfully employed for the experimental design, and statistical analysis was conducted on the obtained experimental results. The microstructural analysis of the sintered composite showed the presence of solid solution phases of Ni and Cr, which were confirmed by the XRD results as (Cr,Ni) alongside unreacted ZrO2 particles at sintering temperatures of 950 °C and 1000 °C. The validity of the model developed with the impact of each variable and their corresponding interaction on the responses was performed using analysis of variance (ANOVA). The relative density and hardness were the two responses considered. The actual values (experiment data) and expected values (simulated data) were subjected to statistical analysis, to develop a predictive model that synchronizes density and hardness as distinct process parameters, with material hardness and relative density serving as the responses of the specified experiment. For the responses, quantitative models were created, and 10 experimental runs were processed to ascertain the desirability of the responses. The SPS processing parameters considered the most desirable were 1000 °C sintering temperature and 50 MPa pressure. The hardness property obtained under this condition is 433.23 HV with a relative density of 98.15%.

Spark plasma sintering and optical properties of Tm3+ and Tm3+ /Yb3+ doped NaLaF4 transparent glass-ceramics

Tm3+ doped oxyfluoride glass-ceramics (GCs) containing NaLaF4 nanocrystals (NCs) have been obtained by spark plasma sintering (SPS). First, the precursor glasses were melted and then milled and sieved to a suitable particle size. Glass powder pellets were sintered by spark plasma sintering under vacuum conditions. The SPS processing parameters (temperature, pressure, and holding time) were optimized to obtain transparent glass-ceramics. The times of SPS processing are considerably shorter compared with those for the preparation of these GCs by conventional thermal treatment. All glass-ceramics contain nanocrystals of the β- NaLaF4 phase with an average crystal size of 20 nm, but the more highly doped samples (2Tm3+ and 0.5Tm3+/2Yb3+) show evidence of the presence of another phase corresponding with α-NaLaF4. The luminescence properties of the near infrared (NIR) emissions of Tm3+ for different concentrations reveal the presence of concentration quenching of the 3H4 and 3F4 levels. The analysis of the decay from the 3H4 level with increasing concentration is consistent with a dipole-dipole quenching process assisted by energy migration, whereas the self-quenching of the 3F4→3H6 emission can be attributed to fast diffusion. Energy transfer between Yb3+ and Tm3+ ions is confirmed by the NIR and upconverted (UC) emissions after Yb3+ excitation at 975 nm. No UC emission is observed under 791 nm excitation of Tm3+ ions.

Dielectric Spectroscopy of Calcium Titanate Processed by Spark Plasma Sintering.

Calcium titanate (CaTiO3) powder was compacted by spark plasma sintering (SPS). The resulting products were subjected to the phase stability study and dielectric characterization. The change in temperature of SPS between 1100 °C and 1250 °C had a clear and straightforward effect on density, porosity, relative permittivity, loss tangent, and DC resistivity. Since the SPS itself introduces certain oxygen deficiency into Ti-perovskites, all samples were annealed after SPS. However, this post-processing did not mask the effects of the SPS regime. Optical reflectance measurements were completed to compare and quantify the sample coloration and support the dielectric results with corresponding optical band gap estimations. Subtle changes in the CaTiO3 crystal lattice arrangement, completed between 1150 °C and 1250 °C and documented in the literature for conventionally sintered samples, could not be confirmed for SPS-prepared calcium titanate. The novelty of this research work is in producing very stable dielectric ceramics and an indication of the SPS processing parameters suitable for this. The best sample showed at 1 MHz frequency the combination of relative permittivity 370, loss tangent 0.008, and DC resistivity 3 × 1012 Ωm.

Optimization of the spark plasma sintering processing parameters of ECR-glass/TiO2/PI nanocomposite using Taguchi design of experiment

This research evaluates the influence of process parameters of the spark plasma sintering (SPS) technique on the densification and hardness properties of ECR/TiO2/PI nanocomposite. Taguchi’s design of experiment was employed for designing the sintering process, while analysis of variance (ANOVA) was adopted to evaluate the contribution of the factor variables to the response variable of hardness and density. 10 wt% ECR-glass and 4 wt% TiO2 were used as reinforcements in the polyimide matrix at varying pressure and temperature for the physical experiment. The sintered samples were examined using a scanning electron microscope, nanoindentation tests, and an Archimedes-based density tester. The optimization was performed on total 9 numbers of runs of experiments. The most desirable SPS processing parameters were recorded at 320 °C and a pressure of 30 MPa. Under this processing condition, a density of 1.49 g/cm3 (relative density of 98.7%), Vickers hardness, and nanoindentation hardness value of 33.46 HV and 361.30 MPa, respectively, were obtained. This research work suggests a facile way to produce high-performance PI nanocomposite for various engineering applications, such as mechanical load-bearing and insulation applications.

Insights on Spark Plasma Sintering of Magnesium Composites: A Review.

This review paper gives an insight into the microstructural, mechanical, biological, and corrosion resistance of spark plasma sintered magnesium (Mg) composites. Mg has a mechanical property similar to natural human bones as well as biodegradable and biocompatible properties. Furthermore, Mg is considered a potential material for structural and biomedical applications. However, its high affinity toward oxygen leads to oxidation of the material. Various researchers optimize the material composition, processing techniques, and surface modifications to overcome this issue. In this review, effort has been made to explore the role of process techniques, especially applying a typical powder metallurgy process and the sintering technique called spark plasma sintering (SPS) in the processing of Mg composites. The effect of reinforcement material on Mg composites is illustrated well. The reinforcement’s homogeneity, size, and shape affect the mechanical properties of Mg composites. The evidence shows that Mg composites exhibit better corrosion resistance, as the reinforcement act as a cathode in a Mg matrix. However, in most cases, a localized corrosion phenomenon is observed. The Mg composite’s high corrosion rate has adversely affected cell viability and promotes cytotoxicity. The reinforcement of bioactive material to the Mg matrix is a potential method to enhance the corrosion resistance and biocompatibility of the materials. However, the impact of SPS process parameters on the final quality of the Mg composite needs to be explored.

Superfast preparation of Al-Sc alloys with high Sc content by spark plasma sintering

Aluminum-scandium alloys with high scandium content by mass were prepared by spark plasma sintering (SPS). The morphology, the phase composition, and the microstructures after sintering at different temperatures of Al-Sc alloy powders were investigated by scanning electron microscope (SEM), energy dispersive spectrometry (EDS), and X-ray diffractometry (XRD). The effect of sintering temperature on the microstructure of Al-Sc alloys was studied in the paper. The results show that, the Al-Sc alloy powders after ball milling are regular with the particle size of 25~45 μm, and the mechanical alloying of Al-Sc alloy powders is realized initially. In addition to the Al and Sc phases, a small amount of Al3Sc and AlSc2 are generated. The spark plasma sintering can realize the rapid densification of Al-Sc alloy with high scandium content, the Al-Sc alloy with 30% Sc by mass is successfully produced by SPS method. By adjusting the SPS process parameters, the relative density of sintered sample can be improved to 92.19%. The samples with the higher density and non-obvious grain boundary are achieved at the sintered temperature above 500℃. The second phases of Al3Sc and AlSc2 are formed by the combination of Sc with the increase of sintering temperature, and the peak intensity of Al3Sc increases gradually.

Porous Al2O3-CNT Nanocomposite Membrane Produced by Spark Plasma Sintering with Tailored Microstructure and Properties for Water Treatment.

Ceramic-based nanocomposite membranes are gaining great attention in various applications, such as water treatment; gas separation; oil and gas, amid their superior fouling resistance and remarkable chemical/thermal stability. Here, we report for the first time the use of spark plasma sintering (SPS) process to fabricate a porous alumina–carbon nanotubes (Al2O3–CNT) nanocomposite membrane for water treatment. The challenge is this work is to achieve a balance between the amount of porosity, desired for a high water flux, and the membrane strength level, required to resist the applied pressure during a water flow experiment. The effect of SPS process parameters (pressure, temperature, heating rate, and holding time) on the microstructure and properties of the developed membrane was investigated and correlated. A powder mixture composed of Al2O3 and 5 wt % CNT was prepared with the addition of starch as a pore former and gum Arabic and sodium dodecyl sulfate as dispersants. The powder mixture was then sintered using SPS to produce a solid but porous nanocomposite membrane. The structure and microstructure of the developed membrane were characterized using X-ray diffraction and field emission scanning electron microscopy. The performance of the membrane was assessed in terms of porosity, permeability, and mechanical properties. Moreover, the adsorption capability of the membrane was performed by evaluating its removal efficacy for cadmium (II) from water. The microstructural analysis revealed that CNT were distributed within the alumina matrix and located mainly along the grain boundaries. The permeability and strength were highly influenced by the sintering pressure and temperature, respectively. The results indicated that the membrane sintered at a pressure of 10 MPa, temperature of 1100 °C, holding time of 5 min, and heating rate of 200 °C/min exhibited the best combination of permeability and strength. This developed membrane showed a significant removal efficiency of 97% for cadmium (II) in an aqueous solution.

Microstructure-oxidation resistance relationship in Ti3AlC2 MAX phase

Spark Plasma Sintering and Hot Isostatic Pressing were used to synthesize coarse-grained and fine-grained Ti3AlC2 specimens. Moreover, Spark Plasma Sintering processing parameters were modified in order to vary the TiC, Al2O3 and TixAly impurity and the porosity contents in the fine-grained samples. The influence of the Ti3AlC2 microstructure on the oxidation resistance was assesed. It is demonstrated that the grain size can drastically modify the oxidation resistance. The higher density of grain boundaries, in fine-grained specimens, increases the number of Al diffusion paths and leads to the formation of a protective alumina scale. In coarse-grained sample, Al diffusion is the rate limiting step of the α−Al2O3 formation and TiO2 is formed simultaneously to alumina. TiC impurities and porosity are demonstrated to be detrimental to the oxidation resistance in the 800 °C–1000 °C temperature range by favouring TiO2 formation. Finally, it is also shown that, for fine-grained specimens, the oxide scale grows very slowly for oxidation times in the range 20–40 days.

Influence of sintering environment on the spark plasma sintering of Maxthal 312 (nominally-Ti3SiC2) and the role of powder particle size on densification

Herein, we report on the synthesis of Ti3SiC2 via the Maxthal 312 (nominally-Ti3SiC2) commercial powder route using spark plasma sintering (SPS). The SPSed bulk samples contained ancillary phases (TiCX and TiSi2) irrespective of the sintering environment as confirmed by XRD phase analysis. The optimum sintering temperature below which intrinsic decomposition starts appears to be ∼1350 °C in vacuum and ∼1450 °C in argon atmosphere, respectively. The role of powder particle size on densification during spark plasma sintering (SPS) was investigated. Analysis of the SPS processing parameters (piston movement and piston speed) indicated that the densification of Maxthal 312 powder (nominally-Ti3SiC2) can be improved by reduction in particle size, thus promoting the Joule effect, necking, mechanical movement of particles and plastic deformation. Further investigation on the role of graphite heating element as well as environment during the SPS synthesis showed that the graphite paper employed during SPS as well as possible silicon loss during vacuum sintering were responsible for the decomposition at temperature below the melting point of Si and/or shifting of the resultant bulk sample composition away from monolithic phase.

Optimization of SPS processing parameters on the density and hardness properties of graphene reinforced polylactic acid nanocomposite

This article examines the influence of process parameters of Spark plasma sintering (SPS) technique on the densification and hardness properties of graphene (GNP) reinforced polylactic acid (PLA) nanocomposite. The numerical experiment was designed in accordance with response surface methodology (RSM) using central composite design (CCD). Five percent GNP were used as reinforcement in the polylactic acid matrix at varying conditions of temperature and pressure for the physical experiment. The validation of the developed model, as well as the effect of each variable and their interaction, was analyzed using the analysis of variance (ANOVA). Taking the material hardness and density as the response of the designed experiment, the data obtained from both the numerical and physical experiment were statistically analyzed to obtain a predictive model which correlates the hardness and density as a function of the independent process parameters. The optimization produced 30 feasible solutions whose desirability equals to 1. The most desirable SPS processing parameters were the temperature of 158.2 °C and a pressure of 25.87 MPa. Under this condition, a density of 1.28 g/cm3 and Vickers hardness value of 260.

Powder metallurgy of stainless steels and composites: a review of mechanical alloying and spark plasma sintering

Although SPS has been studied for a rapidly growing number of materials, there is limited number of researches on the fabrication and microstructural characterization of stainless steels processed by SPS. This article reviewed and provided a critical discussion on the mechanical alloying (MA) and spark plasma sintering (SPS) of dispersion-strengthened stainless steel with emphasis on process parameters, reinforcement efficiencies, microstructural evolutions, and mechanical properties. The influence of spark plasma sintering process parameters on microstructure, phase evolution, and mechanical properties of reinforced stainless steels is reviewed in this work. The role of alloying elements and ceramic reinforcements, their dispersion into the stainless steel matrix, and the importance of matrix-reinforcement interface are highlighted. Current and potential areas of applications of PM stainless steel and suggestions for future research are discussed in this paper.

Optimisation of spark plasma sintering parameters of Al-CNTs-Nb nano-composite using Taguchi Design of Experiment

Optimisation of process parameters is usually undertaken to achieve more efficient and cost-effective process conditions. This work deals with the optimisation of spark plasma sintering process parameters which include sintering temperature, pressure, dwell time and heating rate for the development of Al-CNTs-Nb nano-composite. Taguchi Design of Experiment (DOE) was used to design the sintering operation, while analysis of variance (ANOVA) was used to investigate the contribution of the factor variables to the response variables of density and micro-hardness. The admixed powders were consolidated as designed with SPS machine, while the sintered compacts were characterised using optical microscope, Vickers hardness tester and Archimedes-based density tester. The results obtained were a maximum density of 2.68 g cm−3 (99.3% relative density) and maximum micro-hardness of 38.57 HV (0.37 GPa), while the optimal SPS parameters were sintering temperature of 630 °C, pressure of 30 MPa, dwell time of 10 min and heating rate of 200 °C/min. This work has achieved a 20% improvement in micro-hardness which is good for so many engineering applications.

Optimization of spark plasma sintering parameters for NiTiCu shape memory alloys

ABSTRACTNanostructured nickel titanium copper-shape memory alloys (NiTiCu-SMAs) were fabricated using spark plasma sintering (SPS) by varying the significant process parameters. The NiTiCu elements with different particle size were consolidated in a temperature range of 700–900°C and pressure from 20 to 40 MPa with 5 min of soaking time. The sintered products were subjected to mechanical analysis such as density and microhardness. Genetic algorithm (GA) and particle swarm optimization (PSO) techniques were used with integrated artificial neural network (ANN) to optimize the SPS process parameters to obtain better mechanical characteristics. The results indicate that the density and microhardness can be enhanced by the reduction of particle size and increase in pressure and temperature. A maximum density of 6.21 g/cc and Vickers hardness of 766 Hv were obtained the optimal for process parameters of temperature, pressure, and particle size of ~ 800°C, ~ 26 MPa and ~ 6 µm, respectively, in case of NiTiCu nanostructured SMAs.

Peltier effect during spark plasma sintering (SPS) of thermoelectric materials

Spark plasma sintering (SPS) is a versatile and effective rapid processing technique to sinter nanostructured thermoelectric (TE) materials. This paper presents a combined experimental and modelling investigation of the Peltier effect during SPS processing of TE materials. The Peltier effect is related to the transport of heat by an electric current and produces a temperature gradient. This heat flow manifests itself at the junction between two dissimilar materials at which heat is evolved or absorbed. During SPS processing, the Peltier effect could manifest itself as a significant temperature gradient across the sample. The Peltier effect was found to produce a temperature gradient of 55 °C during the SPS processing of MgSi2 (ZT = 1.4, 3 mm sample thickness) and 60 °C for MnSi1.4 (ZT = 0.4, 3 mm sample thickness). The overall developed experimental and numerical methodology allowed us to confirm the existence of the Peltier effect and to quantify its magnitude. This enabled us to determine a correlation between the SPS process parameters and temperature gradient across the processed TE materials.

Consolidation by spark plasma sintering (SPS) of polyetheretherketone

ABSTRACTThe present study deals with the consolidation of an ultra‐high performance polymer, the poly(ether ether ketone) (PEEK), for structural applications, using the powder metallurgy (PM) way, and more precisely the Spark Plasma Sintering (SPS) processing. The effects of SPS parameters such as temperature, pressure, and dwell time on density and mechanical properties of PEEK were investigated via a Design of Experiments (DoE). A temperature of 250 °C, a pressure of 40 MPa, and a dwell time of 20 min have been identified as the optimal SPS process parameters. In these conditions, a density of 1.31 g/cm3 was reached and homogeneous mechanical properties in the volume determined by means of compression tests were found with a compressive modulus of 2.75 GPa, a yield strength of 134 MPa, and a maximum compressive strain of 43%. These results are better than those of commercial products obtained by injection molding. The pressure appears to be a significant parameter on PEEK properties and plays positive or negative roles according to the responses of DoE studied. To our knowledge, it is one of the first studies based on the application of the PM techniques for PEEK consolidation showing the possibility to process below its melting point. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44911.

Barium titanate nanometric polycrystalline ceramics fired by spark plasma sintering

A series of samples was sintered from nanometric BaTiO3 powder by spark plasma sintering (SPS). Porosity on ultra-fine size scales, hardly accessible for quantification by conventional techniques, was measured by small angle neutron scattering (SANS). Band gap was estimated from diffuse reflectance measurements. Sintered tablets were polished, sputtered by aluminum to create electrode system and tested in DC and AC electric fields. The results were correlated with the SPS processing parameters and are discussed in connection with other BaTiO3 samples produced by SPS with or without additional heat treatment. Majority of our SPS fired samples had, even without subsequent thermal treatment, advantageous combination of high permittivity, DC resistivity and low loss factor, seldom reported for SPS technology.

Effect of the spark plasma sintering parameters, LiF additive, and Nd dopant on the microwave dielectric and optical properties of transparent YAG ceramics

Not only the optical properties, but the microwave dielectric properties of Yttrium aluminium garnet (Y3Al5O12, YAG) ceramics prepared by co-precipitation method combined with spark-plasma sintering (SPS) were investigated by means of adjusting the factors of LiF additive, Nd dopant, and SPS process parameters. Results showed that the in-line transmittance of YAG ceramic with LiF sintered at 1360°C was 81.8% in the infrared range. With increased sintering temperature, the quality factor (Q×f) and dielectric constant (εr) values of the pure YAG ceramics increased to the maximum and then decreased. The optimal microwave dielectric properties (Q×f=89,810GHz, εr=10.63 and τf=−51.4ppm/°C) are achieved for transparent YAG ceramics sintered at 1360°C. The Q×f values of Nd:YAG ceramics were lower than those of the pure YAG ceramics. The optimal microwave dielectric properties of 2at.%Nd:YAG ceramic cylinder can be obtained with the Q×f of 64,026GHz, εr of 10.2 and τf of −64.8ppm/°C.

Optimization of the spark plasma sintering processing parameters affecting the properties of polyimide

ABSTRACTThe present study deals with the optimization of polyimide (PI) mechanical properties, obtained by Spark Plasma Sintering (SPS), by using a method combining Design of Experiments (DOE) with physical, structural, and mechanical characterizations. The effects of SPS parameters such as temperature, pressure, dwell time, and cooling rate on the density, mechanical properties, and structure of PI were investigated. The experimental results revealed that the mechanical properties of the material were optimized by raising the sintering temperature up to 350°C. The optimized SPS processing parameters were a temperature of 350°C, a pressure of 40 MPa, and a dwell time of 5 min. Under these conditions, a relative density of 99.6% was reached within only a few minutes. The corresponding mechanical properties consisted of Young's modulus of 3.43 GPa, a Shore D hardness of 87.3, and a compressive strength of 738 MPa for a maximum compressive strain of 61.8%. Moreover, when working at 320°C and at 100 MPa, an increase in the dwell time was necessary to enhance the properties. Contrary to the other parameters, the cooling rate appeared to be a non‐significant parameter. Finally, correlations between the PI structure and the mechanical properties were made to demonstrate the densification mechanisms. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41542.

A tough graphene nanosheet/hydroxyapatite composite with improved in vitro biocompatibility

Mechanical properties and in vitro biocompatibility of graphene/hydroxyapatite (HA) composite synthesized using spark plasma sintering (SPS) are reported in this study. Raman spectroscopy corroborated that graphene nanosheets (GNSs) survived the harsh processing conditions of the selected SPS processing parameters. A 1.0wt.% GNS/HA composite exhibits ∼80% improvement in fracture toughness as compared to pure HA. GNS pull-out, grain bridging by GNS, crack bridging and crack deflection are the major toughening mechanisms that resist crack propagation. In vitro osteoblast growth tests illustrate that the added GNSs contribute to the improvement of both osteoblast adhesion and apatite mineralization. Therefore, the GNS/HA composite is expected to be a promising material for load-bearing orthopedic implants.