Spark Plasma Sintering Process Research Articles

Modulation of dielectric properties of hexagonal/cubic boron nitride composites

In this work, we synthesized mixed-phase hexagonal-boron nitride (h-BN)/cubic-BN (c-BN) composites with varying ratios and investigated their frequency and temperature-dependent dielectric properties. As the ratio of c-BN increased, we observed a corresponding increase in the dielectric constant of the composites. Furthermore, we used spark-plasma sintering (SPS) to treat the mixed-phase composite, which resulted in a phase transformation from mixed phase to pure h-BN phase. Remarkably, the composite exhibited an increase in dielectric constant after the SPS process, which can be attributed to the densification of the composite and the enhancement in grain size. Our approach presents a promising strategy for effectively modulating the dielectric properties of BN, which is crucial for advanced electronics.

Enhancing Transparency in Non-Cubic Calcium Phosphate Ceramics: Effect of Starting Powder, LiF Doping, and Spark Plasma Sintering Parameters

Our objective is to achieve a new good-quality and mechanically durable high-transparency material that, when activated by rare earth ions, can be used as laser sources, scintillators, or phosphors. The best functional transparent ceramics are formed from high-symmetry systems, mainly cubic. Considering hexagonal hydroxyapatite, which shows anisotropy, the particle size of the initial powder is extremely important and should be of the order of several tens of nanometers. In this work, transparent micro-crystalline ceramics of non-cubic Ca10(PO4)6(OH)2 calcium phosphate were fabricated via Spark Plasma Sintering (SPS) from two types of nanopowders i.e., commercially available (COM. HA) and laboratory-made (LAB. HA) via the hydrothermal (HT) protocol. Our study centered on examining how the quality of sintered bodies is affected by the following parameters: the addition of LiF sintering agent, the temperature during the SPS process, and the quality of the starting nanopowders. The phase purity, microstructure, and optical transmittance of the ceramics were investigated to determine suitable sintering conditions. The best optical ceramics were obtained from LAB. HA nanopowder with the addition of 0.25 wt.% of LiF sintered at 1000 °C and 1050 °C.

Synergetic enhancement of ultimate strength and damping properties by pore structure in novel porous Cu-Al-Mn shape memory alloy

To meet the higher device vibration reduction requirements, novel porous Cu71Al18Mn11 shape memory alloys (SMAs) with controllable porosity were prepared using Cu, Al, and Mn elemental powders as raw materials. To further enhance the strength and damping performance of SMAs, a low-temperature reactive synthesis combined with spark plasma sintering (LTRS+SPS) process was used. In this paper, the effects of LTRS+SPS process on pore structure and texture, compressive strength, and damping properties of porous Cu71Al18Mn11 alloy were studied. The outcomes indicated that LTRS+SPS process can effectively improve both compressive strength and damping properties. The associated closed pore structure caused by this process and the second phase γ2 phase formed by element diffusion result in a variety in compressive strength from 324.6 MPa to 617.9 MPa, which were 3.9 times that of the comparable porosity alloy with alloy powder as raw material by vacuum sintering. Meanwhile, the damping value changed from 0.27 to 0.10, which was 4.5 times that of the homogeneous dense alloy. The increase in damping property is caused by the increase of motionable interfaces in the matrix for the introduction of pores, which leads to the increase of energy dissipation. Besides. the interaction between the second phase γ2 and dislocation contributes to the improvement of damping, as well as the compressive strength. These findings in this paper provide new insights and references for the structural design and microstructure design of high-performance Cu-based alloys.

Realization of high cryogenic thermoelectric performance for MgAgSb base alloy by regulation heat-treatment process

MgAgSb alloy has attracted wide attention due to its inherent low thermal conductivity, excellent thermoelectric (TE) properties, and environmental friendliness. Although the TE performance has been deeply investigated for the temperature range over 300–700 K, while cryogenic range has seldom report. In this study, a systematic investigation on cryogenic TE performance of α-MgAgSb has been performed. α-MgAgSb alloy has been synthesized by ordinary ball milling followed spark plasma sintering process and then further regulated by heat treatment. The power factor of MgAgSb alloy after 10 days of heat-treating increased by 230%, which is attributed to the reduction of the impurity phase and the improvement of the crystallinity achieved by the optimization of heat treatment. The total thermal conductivity decreased by 18% to 1.15 W m−1 K−1, and the maximum ZT reached 0.264 at 173 K, which is 300% enhancement to untreated one. The ZTavg reached to 0.45 over 173–298 K, located at the pinnacle among cryogenic TE materials. In addition, the ZTeng value of 0.23 related to the highest device conversion efficiency of 5.2% demonstrates good device potential. This work reveals that the purity and the cryogenic TE properties of α-MgAgSb alloy can be effectively improved by heat-treating, and demonstrates the greatly potential of MgAgSb materials in the field of liquefied natural gas's cold energy recovery.

Microstructural Evolution and Densification of Co-Based Alloy Powder by Spark Plasma Sintering for High-Hardness Applications

This work presents the densification of Co-based alloy powders by a spark plasma sintering process. The densification process was carried out at a temperature range of 800 °C to 1100 °C in order to obtain sintered coupons and study their microstructure and mechanical properties. The shrinkage behaviour of the sintered coupons was studied, and an optimal densification temperature was defined. The microstructural analysis showed a reduction in porosity with temperature increment along with the development of a fine microstructure comprised of cobalt-molybdenum-chromium-silicon-based intermetallic laves phases, which are dispersed in a softer cobalt-based alloy matrix. X-diffraction analysis showed that these crystalline phases were well-dispersed, with a lattice parameter corresponding to a hexagonal system. The obtained high Vickers hardness values were attributed to the preservation of a fine microstructure and to the precipitation of Co-Mo phases. Three-point bending tests were performed in order to identify the strain path concerning the densification of the sintered coupons.

Spark plasma sintering in the presence of a liquid phase

Spark plasma sintering (SPS) is a modern sintering technique based on the application of pulses of direct electric current and pressure to the powder sample. SPS is often regarded as a solid state sintering technique. At the same time, in many studies, the formation of a liquid phase during SPS was observed as an effect concurrent to the powder consolidation. Furthermore, in some cases, the formation of a liquid phase was intentionally stimulated. In this article, we aim to analyze the origin of the liquid phase formation during SPS and discuss its role in the microstructure development of different materials. Two situations are considered: melting occurring when the whole sample reaches a temperature required for the liquid to appear and melting of local character associated with overheating of the inter-particle contacts. The problems of the description of the SPS processes with liquid phases involved are discussed and possible future research directions in this area are proposed.

Tuning mechanical and electrical performances of B 4C–TiB 2 ceramics in a two-step spark plasma sintering process

Tuning mechanical and electrical performances of B ₄C–TiB ₂ ceramics in a two-step spark plasma sintering process

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.

Electrothermal Simulation of the Production of Alumina by Spark Plasma Sintering

Although the spark plasma sintering (SPS) method is a very advantageous technque in many aspects, the inability to clearly read the temperature formed on the material during sintering and heterogeneous temperature distributions are the biggest problems of this process. Therefore, it is a common situation that samples taken from different regions of the produced material have different densities and mechanical properties. In this study, the temperature distributions, current density and joule heating effect of the entire setup consisting of the alumina (Al2O3) sample to be sintered, inconel electrodes, graphite dies, punches and spacers, as well as the critical regions in this setup, are modeled by using finite element software. According to the results, the temperature is maximum at the centre of the Al2O3 sample and the temperature gradient along its radius is 22.4°C. The temperature difference between the inner wall of the hole which is opened in the graphite mold to measure the sintering temperature and the centre of the Al2O3 sample is around 40°C. In addition, during the SPS process, Al2O3 is not heated directly by the joule effect and the temperature gradient in the sample occurs due to mold surface radiation.

Effects of die geometry and insulation on the energy and electrical parameters analyses of spark plasma sintered TiC ceramics

This work conducts a numerical simulation to investigate the temperature and electric current distribution during the spark plasma sintering (SPS) process using the finite element method (FEM) carried out in COMSOL Multiphysics software. The main goal is to optimize the SPS process for titanium carbide (TiC) ceramics, with a particular focus on the effects of insulation and die geometry (height and thickness). For the TiC material, the ideal sintering temperature is set at 2000 °C. The study analyzes eight case studies, involving a base case, an insulating case, and six cases with various thicknesses and heights, in order to evaluate the effectiveness of the suggested optimization. The results show that using insulation on the die surface reduces heat transfer from the die surface significantly, which leads to a 63% decrease in input power consumption when compared to the basic scenario. Based on a correlation study between energy and electricity, increasing die thickness raises the cross-sectional area of the electric current, which raises the amount of electric power required to attain the 2000 °C sintering temperature. The results indicate the temperature distribution in the sample is more sensitive to changes in die height than to changes in die thickness.

Using the Spark Plasma Sintering System for Fabrication of Advanced Semiconductor Materials.

The interest in the Spark Plasma Sintering (SPS) technique has continuously increased over the last few years. This article shows the possibility of the development of an SPS device used for material processing and synthesis in both scientific and industrial applications and aims to present manufacturing methods and the versatility of an SPS device, presenting examples of processing Arc-Melted- (half-Heusler, cobalt triantimonide) and Self-propagating High-temperature Synthesis (SHS)-synthesized semiconductor (bismuth telluride) materials. The SPS system functionality development is presented, the purpose of which was to broaden the knowledge of the nature of SPS processes. This approach enabled the precise design of material sintering processes and also contributed to increasing the repeatability and accuracy of sintering conditions.

Feasibility of using Ni25Co20Cu10Fe25Mn20 high entropy alloy as a novel sintering aid in ZrB2 ceramics

For the first time, Ni25Co20Cu10Fe25Mn20 high entropy alloy (HEA) was employed as a sintering aid for fabrication of ZrB2-based ceramics using spark plasma sintering (SPS) process. The mechanical properties, phase evolution, microstructural changes, and the densification mechanisms of ZrB2-5 wt% HEA ceramics during the SPS step were scrutinized. The ZrB2-5 wt% HEA ceramic, manufactured at 1900 °C, yielded interesting combination of properties, counting a relative density of 96%, a fracture toughness of 6.4 MPa m1/2, and a hardness of 12.6 GPa. According to XRD patterns, there were ZrC and ZrO2 phases with ZrB2 matrix in the sintered samples. An unknown phase was also observed in the XRD patterns. Based on the history of the NiCoCuFeMn alloy and separation of Cu within the temperature range of 650–850 °C, that phase was related to CuB.

Process Optimization of Spark Plasma Sintered Parameters for Ti-Al-Cr-Nb-Ni-Cu-Co High Entropy Alloy by Response Surface Methodology

In this study, the influence of operating parameters on the relative density and microhardness property of a septenary equiatomic Ti-Al-Cr-Nb-Ni-Cu-Co high entropy alloy developed via spark plasma sintering (SPS) process was investigated at constant heating rate (100 °C/min), dwell time (5 min), pressure (50 MPa). Using response surface methodology (RSM) on the sintering temperature (ST) and milling time (MT) as the process variable parameters, a predictive model was established. The design of experiment approach was employed to minimize numbers of runs of experiment, which invariably eliminates trial by error associated with traditional experimental methods. MT and ST were taken as the variables towards the development of the design model. The optimum operating parameters were predicted using the user-defined design (UDD) under RSM and the result was validated through experiments. Observation from the results shows that MT and ST play a significant role in achieving high densification, which translates to high hardness. At 900 °C ST and MT of 10 hours, the highest hardness value of 580.1 HV, densification of 99.98%, and percentage porosity of 0.02% were recorded.

Tunable yellow and orange emission of Ce, Eu doped multilayered YSZ/YAG ceramics

Eu3+ and Ce3+ doped YSZ/YAG multilayered luminescent ceramics were consolidated by the Spark Plasma Sintering (SPS) method. The optimal modes were explored during the SPS process for functionally graded ceramics (FGCs) structure fabrication. The introduction of rare-earth (RE) oxides into FGCs with different concentration leads to a shift in the temperature range of intense shrinkage to lower temperatures from 1280 °C to 1100–1190 °C and a decrease in the relative shrinkage during the SPS process by 3–6%. Morphological, optical and luminescent properties have been investigated in detail for fabricated YSZ/YAG ceramics with different arrangement of the layers. The nature of luminescent centers in FGCs was studied using time-resolved cathodoluminescent and steady-state photoluminescent (PL) spectroscopy. The PL efficiency of YSZ/YAG ceramics were analyzed and optimal compositions of the FGCs layers were determined. The YSZ/YAG novel functional multilayered ceramics could be promising candidate for light-emitting devices application.

Ultra-high-performance graphene-based bulk materials strengthened by Y-type connection structure

The strategic design and assembly of bulk graphene materials represent a pivotal advancement for harnessing the inherent properties of graphene in practical applications. However, fabricating high-strength graphene-based bulk materials from graphene powders presents a significant challenge, primarily due to interlayer slippage between the graphene layers. Here, a unique Y-type connection structure was found in few-layer graphene synthesized by self-propagating high-temperature synthesis (SHS) and subsequently retained in graphene-based bulk materials prepared by spark plasma sintering (SPS) process. The Y-type connection structure and defect-induced linkages serve to cross-link the graphene-based bulk materials. Consequently, the bulk material exhibited an ultra-high compressive strength, reaching 2.14 GPa, supported by Molecular dynamics (MD) simulations which demonstrated that the Y-type connection structure increases the shear modulus and the load transfer rate. The Y-type connection structure plays a vital role in reinforcing the strength of graphene-based bulk materials, offering valuable insights for the microstructural design and property augmentation of other graphene-derived materials. Besides it’s ultra-high compressive strength, the graphene-based bulk material also performs a low thermal expansion coefficient (0.5 × 10−6 K−1), high electrical conductivity (1.47 × 105 S·m−1) and exceptional EMI shielding capability.

The investigation of synthesis and textured properties of in situ formed hBN with spark plasma sintering

Hexagonal boron nitride (hBN) exhibits high thermal conductivity within the in-plane direction and significantly lower thermal conductivity in the cross-plane direction because of its anisotropic nature. When the texture properties of bulk hBN are strong, it is a potentially promising application area for the insulating heat spreaders and heat sinks. In this study, hBN was synthesized in situ with the spark plasma sintering (SPS) technique and the effects of sintering temperature on the orientation of hBN grains were investigated. The precursor was prepared by chemically reacting urea and boric acid in heat treatment at 850 °C. The hBN was produced using the previous precursor in a SPS at 1500, 1700, and 1900 °C. The samples were characterized using XRD, FTIR, SEM and Raman spectroscopy. The properties of the samples were further determined through measurements of density, DSC and thermal diffusivity. The hBN samples obtained through the SPS process have nano and micron-size grains. The hBN was highly crystalline and homogeneous, as determined by the XRD pattern, Raman spectra and Raman maps. The orientation of hBN grains has been revealed in the c-axis of hBN crystallites and was preferably arranged within a plane parallel to the SPS pressing direction. The hBN orientation preference index (IOP) value of −19925.5 at 1700 °C indicates the highest quality texture orientation. Increasing the temperature to 1900 °C decreased the orientation in the direction parallel to the pressing direction. The highest thermal conductivity calculated according to the thermal diffusivity perpendicular to the sintering pressure direction was 8.86 W m−1K−1 at 1900 °C.

Fretting wear characteristics of Ti6Al4V/TiC nano composites using response surface method

This study explores the impact of titanium carbide (TiC) nanoparticles on the microstructure and fretting wear performance of Ti64-GV alloys. The Ti64 alloys, featuring varying TiC concentrations, were fabricated through spark plasma sintering (SPS) process. Fretting experiments followed a face-centered central composite design methodology, employing a second-order quadratic regression model to analyze wear volume loss and coefficient of friction (CoF). The findings revealed a notable reduction in wear volume loss and friction coefficient with increasing TiC content. The presence of TiC significantly enhanced the wear resistance of Nano-composites due to heightened hardness and oxidation wear resistance. Employing hybrid desirability-based response surface methodology (RSM) led to substantial improvements in wear characteristics (37% in CoF and 46% in wear volume loss). Microstructural analysis affirmed enhanced surface quality and textures using the RSM hybrid approach for predicting optimal process parameters.

Investigation of the mechanical, thermal and dielectric properties of electrical corrosion resistance glass reinforced polyimide-based composite produced by spark plasma sintering

Polyimide polymer matrix composites have gained numerous attentions in the design and fabrication of components for automobile, aerospace, and electronics applications as a result of their outstanding properties. Composites are currently replacing polymers as structural, insulation and dielectric materials, and the improvement of mechanical, thermal, and dielectric properties of polyimide (PI) becomes important. Thus, in this paper, the enhancement of the mechanical, thermal stability, and dielectric properties of PI composites with boron-free E-glass (electrical corrosion resistance (ECR) glass) reinforcements (0, 5, 10, and 15 wt%) using Spark Plasma Sintering (SPS) process is presented. X-ray diffractometer, scanning electron microscope (SEM), nanoindentation tests, thermogravimetric analyser, and LCR meter tester were used to investigate the morphology, mechanical, thermal, and dielectric properties of the developed composites, respectively. The SEM results revealed that the ECR-glass powder particles were well dispersed in the PI matrix. The introduction of the ECR into the PI matrix, improves its hardness, stiffness, and modulus. From the obtained results, a notable improvement in its hardness (9.36%), stiffness (30.77%), and modulus (43.58%) was revealed for ECR/PI loaded with 15 wt% ECR compared to pure PI. The thermal stability of the PI composites was observed to be improved with the incorporation of the ECR-glass particles. The heat resistance index of the PI was recorded to be improved by 3.8% at 15 wt% ECR incorporation. Furthermore, the composites depicted low dielectric constant and dissipation factor. In consideration, the obtained properties make the composites promising for mechanical load-bearing, thermal management and electronics applications.

Influence of TiCp ceramic reinforcement on Ti6Al4V alloy matrix via spark plasma sintering technique

ABSTRACT The present approach focuses to explore the effect of TiCp nano particulates reinforcement (with various percentages 0%, 0.5%, 1%, 1.5%, 2% & 2.5%) on the microstructure and mechanical behaviour of Ti6Al4V alloys. The spark plasma sintering (SPS) process has been implemented with an applied pressure of 80MPa, sintering temperatures range from 1050°C to 1160°C, with heating rate of 100°C/min, and a dwell time of 5 min at peak temperature to fabricate the nano composites. X-ray diffraction (XRD) and FE-SEM equipped with Energy Dispersive X-ray Analysis (EDAX) were used to examine the newly prepared TMC’s. The sintered Ti6Al4V/TiCp composites showed diverse distributions of TiCp nano-particle in the matrix alloys and were found to exhibit dense, pore-less microstructure. As new phases are developed, the properties of the composite materials’ underwent significant changes.

Regulated Phase Separation in Al-Ti-Cu-Co Alloys through Spark Plasma Sintering Process.

With the goal of developing lightweight Al-Ti-containing multicomponent alloys with excellent mechanical strength, an Al-Ti-Cu-Co alloy with a phase-separated microstructure was prepared. The granulometry of metal particles was reduced using planetary ball milling. The particle size of the metal powders decreased as the ball milling time increased from 5, 7, to 15 h (i.e., 6.6 ± 6.4, 5.1 ± 4.3, and 3.2 ± 2.1 μm, respectively). The reduction in particle size and the dispersion of metal powders promoted enhanced diffusion during the spark plasma sintering process. This led to the micro-phase separation of the (Cu, Co)2AlTi (L21) phase, and the formation of a Cu-rich phase with embedded nanoscale Ti-rich (B2) precipitates. The Al-Ti-Cu-Co alloys prepared using powder metallurgy through the spark plasma sintering exhibited different hardnesses of 684, 710, and 791 HV, respectively, while maintaining a relatively low density of 5.8-5.9 g/cm3 (<6 g/cm3). The mechanical properties were improved due to a decrease in particle size achieved through increased ball milling time, leading to a finer grain size. The L21 phase, consisting of (Cu, Co)2AlTi, is the site of basic hardness performance, and the Cu-rich phase is the mechanical buffer layer between the L21 and B2 phases. The finer network structure of the Cu-rich phase also suppresses brittle fracture.