Spark Plasma Sintering Temperature Research Articles

Understanding the Individual Role of Composition and Spark Plasma Sintering Temperature on the Microstructure and Hardness of Alumina–Zirconia Composites

Understanding the Individual Role of Composition and Spark Plasma Sintering Temperature on the Microstructure and Hardness of Alumina–Zirconia Composites

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.

The effects of sintering temperature on the microstructural evolution and mechanical properties of yttrium hydride monoliths via spark plasma sintering

In recent years, yttrium hydride has garnered significant attention due to its remarkable thermal stability and potential for high hydrogen density. It is regarded as one of the most promising metal hydrides for use as a neutron moderator in microreactors. In this study, yttrium hydride monoliths were synthesized using yttrium hydride powder obtained through direct hydrogenation, facilitated by Spark Plasma Sintering (SPS) at temperatures ranging from 800 to 1200 ℃. The effects of SPS temperatures on the phase composition, microstructure, density, and mechanical properties of yttrium hydride monoliths were studied. The results show that the sintering temperature markedly impacts the hardness, pore evolution, grain size and precipitation of α-Y and Y2O3 phase. Notably, the hardness of the samples escalates significantly with an increase in sintering temperature below 1000 ℃, influenced by a reduction in both the number and size of pores. The occurrence of twin crystals, distribution of grain size and the phase-transformed particles of α-Y within the sintered sample may contribute to an increase in hardness. The procedures described herein affect developing important microstructure-property relationships, as well as correlations in the sintering parameters and mechanical properties.

Carbon contamination of elemental beta-boron promoted a stable boron carbide by spark plasma sintering

The effect of carbon contamination on the elemental beta boron (β-B) from the graphite components of spark plasma sintering (SPS) was investigated. The X-ray diffraction, analytical electron microscopy (AEM) and Raman spectroscopy witnessed boron carbide (B13+xC2-x where x=0.05–0.35), when SPS temperature was above 1750 °C. The degree of carbon contamination became severe with increasing SPS temperature to 1800 °C and 1850 °C and formed a single-phase rhombohedral boron carbide with about 12 wt% of carbon. Our observations indicate that the carbon gets kinetically trapped into β-B to form boron carbide with a primitive unit cell consisting mainly of icosahedral B11C and three-atom chain of CBB configurations. After 6 months of natural aging, it has been revealed that boron carbide formed at and below sintering temperatures of 1800 °C is not a thermodynamically stable phase, and transformed reversibly to β-B structure. X-ray photoelectron spectroscopy ascertained that there are no longer B-C bonds and the existence of more CC bonds in a 6 months aged specimen, suggesting carbon is no longer strongly bonded to boron, but precipitates as graphitic structure. Further examination using atom probe tomography and AEM confirmed the existence of carbon nanoclusters within grains and high concentration of carbon segregating onto grain boundaries. The phase transformation of boron carbide to mostly boron resulted in a significant loss of hardness and modulus in a bulk SPS specimen. This study underscores the importance of solid solution and local bonding environment in icosahedral boron-rich solids for phase stability and sustained properties.

Effect of Spark Plasma Sintering Temperature on the Microstructure and Thermophysical Properties of High-Silicon–Aluminum Composites

Spark plasma sintering is a process of rapid, low-temperature, and high-density sintering. Moreover, traditional sintering methods can solve the problems of large grain sizes and low densities. The sintering temperature plays a crucial role in influencing the physical properties of high-silicon–aluminum (Si-Al) composites. This work investigated the impact of temperature on the microstructure, interface, and physical properties of high-Si-Al composites by spark plasma sintering. The results demonstrate that when the powder was processed by ball milling at a sintering temperature of 565 °C, the material exhibited the densest microstructure with minimal pore formation. The average size of the silicon phase is the smallest. The material’s thermal conductivity is 134.6 W/m·K, the thermal expansion coefficient is 8.55 × 10−6 K−1, the Brinell hardness is 219 HBW, the density is 2.415 g/cm3, and the density reaches 97.75%. An appropriate sintering temperature facilitates particle rearrangement and dissolution–precipitation processes, enhancing the material structure and performance.

Fabricating ultrahard boron carbide–silicon carbide–zirconium diboride composites by spark plasma sintering from B4C with ZrSi2 aids

Triplex-particulate ceramic composites with varying proportions of boron carbide plus SiC and ZrB2 second phases were fabricated by transient liquid-phase assisted spark plasma sintering (SPS) from B4C with 5–30 vol% ZrSi2 aids, optimising the SPS temperatures and identifying the so far elusive carbon source for the in situ formation of most of the SiC in these composites and in their boron carbide–SiC–metal diboride counterparts. Firstly, it is shown that ZrSi2 is a suitable sintering additive that significantly reduces the SPS temperatures of B4C, making densification possible at temperatures in the range 1500–1750 °C (the more ZrSi2 aid, the lower the SPS temperature) at which pure B4C is unsinterable. Secondly, it is shown that ZrSi2 is a reactive sintering additive that reacts with part of the starting B4C to form SiC, ZrB2, and Si, the latter being a transient phase that first contributes to densification by liquid phase sintering and then disappears upon reaction with the remaining B4C to form more SiC and a Si-doped B-rich boron carbide. Carbon exsolution from B4C is thus the carbon source for the formation of most of the SiC. Thirdly, it is shown that the thus-fabricated triplex-particulate composites are ultrahard (>30 GPa) when B4C is SPS-ed with 20 vol% ZrSi2 or less, and that the one SPS-ed from B4C with 20 vol% ZrSi2 has the best trade-off between sinterability (SPS at 1600 °C) and super-hardness (∼32.4 GPa). Finally, a comparison is made between these and other existing triplex-particulate boron carbide–SiC–metal diboride composites.

Synthesis and analysis of the magnetic properties of YIG by means of sol–gel and spark plasma sintering

We presented a study on the structure and magnetic properties of yttrium iron garnet (YIG), Y3Fe5O12, which was synthesized by means of sol–gel method and spark plasma sintering (SPS). The YIG nanoparticles were prepared by sol–gel method followed by 800 °C annealing for 3 h. SPS procedures with different temperatures (700 °C∼900 °C) and holding times (30 min ∼ 90 min) were performed to study the influence of SPS conditions on the structure and magnetic properties of YIG. The X-ray diffraction pattern and Raman spectrum confirmed the presence of YIG at all studied conditions. All samples were pure garnet phase except for the samples with too high temperatures (900 °C) and too long holding time (90 min). The impurities were inferred to be due to the hypoxic environment caused by the vacuum sintering condition of SPS. The magnetic properties of YIG samples were significantly affected by SPS conditions. The YIG sample became multi-domain at the temperature as low as 750 °C and grew to 89.1 nm at 850 °C for 30 min holding time benefiting from to the special sintering effect of SPS. Large particles with loose texture were formed by the formation of sintering neck between the adjacent particles when the SPS temperature was higher than 800 °C. It are confirmed that the sample with extended holding time at a moderate temperature (800℃/60 min) show the best soft-magnetic properties, whose Ms, Mr and Hc are 27.5 emu/g, 2.4 emu/g and 19.2 Oe respectively. The results show that this method has good potential in preparing YIG with good magnetic properties.

Oxygen vacancy-activated thermoelectric properties of ZnO ceramics

Understanding the structural and thermoelectric (TE) properties of a pure material is essential for developing a practical approach to improve its TE performance. This study focuses on the high-temperature TE properties of ZnO ceramics synthesized by the spark plasma sintering (SPS) technique. The analyses of crystallinity and microstructure along with photoluminescence and Raman spectroscopy indicated an increase in oxygen vacancy in the ZnO ceramics with SPS temperature, which resulted in unit-cell shrinkage, lattice modification, grain densification, and TE modification. Specifically, oxygen vacancies were found to be a crucial factor affecting the TE performance of the spark-plasma-sintered ZnO ceramics at temperatures exceeding 773 K. Oxygen vacancies can act as carrier donors when they are ionized, contributing to an increase in electrical conductivity and a decrease in thermal conductivity. Additionally, this study proposes a potential way to engineer native defects in ZnO ceramics by controlling the SPS process.

Fabricating exotic boron carbide ceramics by shaker milling and reactive spark plasma sintering of B and C: Application to the elusive B6C

A route based on the shaker milling of B and C powders followed by reactive spark plasma sintering (SPS) of the resulting B+C powder mixture is presented for the fabrication of exotic boron carbide monolithic ceramics with controlled stoichiometry, and applied to the elusive B6C ceramics. Firstly, it is shown that shaker milling for only 1 h refines down to the nanoscale, mechanically activates, and intimately mixes the B and C powders, making the resulting B+C powder mixture far more sinterable. Secondly, it is shown that B and C react during the heating ramp of the SPS cycles, resulting in a fully dense superhard (∼30 GPa) boron carbide monolith with the desired stoichiometry (B6C in this case) and fine twinned-grain microstructure at an SPS temperature (1550 °C in this case) at which typical commercial B4C powders barely densify. This low-temperature densification is possible mainly due to the enhanced solid-state sinterability promoted by both shaker milling and structural ordering, with the exothermic heat released during the formation of the boron carbide contributing little. And thirdly, it is shown that there is an optimal SPS temperature above which the hardness of these exotic boron carbide monoliths decreases because there is less twinning hardening.

Investigation of Spark Plasma Sintering on Microstructure-Properties of Zirconia Reinforced Fluormica Glass for Dental Restorations.

Conventional sintering methods of dental ceramics have limitations of high temperature and slow cooling rates with requirements of additional heat treatment for crystallization. Spark plasma sintering (SPS) is an emerging technique that has the potential to process dental restorations with dense microstructures and tailor-made clinically relevant properties with optimized processing parameters. This study explored the potential of the SPS of zirconia-reinforced fluormica glass (FM) for dental restorative materials. FM glass frit was obtained through the melt-quench technique (44.5 SiO2-16.7 Al2O3-9.5 K2O-14.5 MgO-8.5 B2O3-6.3 F (wt.%)). The glass frit was ball-milled with 20 wt.% of 3 mol% yttria-stabilized zirconia (FMZ) for enhanced fracture toughness. The mixtures were SPS sintered at a pressure of 50 MPa and a heating rate of 100 °C/min for 5 min with an increase in temperature from 650-750 °C-850 °C-950 °C. Phase analysis was carried out using XRD and microstructural characterization with SEM. Micro-hardness, nano-indentation, porosity, density, indentation fracture toughness, and genotoxicity were assessed. The increase in the SPS temperature of FMZ influenced its microstructure and resulted in reduced porosity, improved density, and optimal mechanical properties with the absence of genotoxicity on human gingival fibroblast cells.

The Influence of Ball Milling Time and Sintering Temperature on the Structural and Capabilities of FeCoCrNiMn High-Entropy Alloy

This study reports the fabrication of FeCoCrNiMn high-entropy alloy using high-purity powders of Fe, Co, Cr, Ni, and Mn through the processes of mechanical alloying (MA) and spark plasma sintering (SPS). We systematically investigated the effects of different ball milling times (10 h, 20 h, 30 h, 40 h, 50 h) and sintering temperatures (700°C, 800°C, 900°C, 1000°C, 1100°C) on the structure and capabilities of the alloy. The findings indicate that the atomic proportion of Fe:Co:Cr:Ni:Mn approach 1:1:1:1:1. The distribution of all elements is basically uniform, but the Cr element is slightly biased in the structure after 40 h ball milling. The voids in the structure are gradually decreasing as temperatures rise. The matrix structure is mainly composed of a white FCC matrix phase and a gray Cr-rich σ phase. The alloy structure is the densest. It has the highest density of 7.060 g/cm3, the highest compressive strength of 1480 MPa, and a plastic deformation of 13% when the SPS temperature reaches 1000°C. The FeCoCrNiMn high-entropy alloy is prepared by a ball milling time of 40 h, and spark plasma sintering of 1000°C has the best comprehensive properties.

Spark plasma sintering of graphite-chromium carbide composites: Influence of the sintering temperature and powder synthesis method

Carbon-metal carbide composites are a novel family of materials with potential application in heat dissipation due to the lightness and thermal-mechanical properties. Within these composites, those of graphite-chromium carbide have been still few studied. Therefore, this research focuses on both the influence of the powder preparation method (mechanical mixing (MM) and colloidal synthesis (CS)) and the spark plasma sintering (SPS) temperature (1600, 1700, 1800, 1900 and 2000 °C) in the properties of the composite graphite-7 vol. Cr. Results indicate that the composites sintered from powders processed by CS exhibit better properties, which can be explained by the better dispersion of the chromium carbide, formed during the sintering process, in the matrix of composite. Apart from the powder preparation method, sintering temperature has influence on the properties of the composite: 1900 °C is the best in the case of the route CS + SPS, while 2000 °C is the best option in the route MM + SPS. The thermal conductivity in-plane is 1.75 times greater in the CS than in the MM route, which suggests a better performance in the composite processed by colloidal route in heat dissipation applications.

Micro-/nano-scale WC particle-reinforced Cu-based composite preparation and property study

In this paper, Cu-based composites were prepared by the powder metallurgy method with the spark plasma sintering (SPS) sintering technique using WC (tungsten carbide) particles as the reinforcing phase and Cu as the matrix. The effect of sintering temperature on the electrical and mechanical properties of the composites was investigated, and the effect of the variation in the reinforcing phase content on the electrical and mechanical properties of the composites was investigated at the optimum sintering temperature. The microstructure and properties of 5 wt. % WC/Cu composites at different sintering temperatures were investigated, and 850 °C was determined as the optimum sintering temperature. When the SPS temperature was 850 °C, the yield strength, compressive strength, compressive strain, and hardness of 10 wt. % WC/Cu composites were 321 MPa, 743 MPa, 40.42%, and 143.2 HV, respectively, which increased the yield strength and compressive strength by 697.82% and 246.84%, respectively, compared with pure Cu material.

Synthesis of Tungsten Carbides in a Copper Matrix by Spark Plasma Sintering: Microstructure Formation Mechanisms and Properties of the Consolidated Materials.

In this study, the synthesis of tungsten carbides in a copper matrix by spark plasma sintering (SPS) is conducted and the microstructure formation mechanisms of the composite materials are investigated. The reaction mixtures were prepared by the high-energy mechanical milling (MM) of W, C and Cu powders. The influence of the MM time and SPS temperature on the tungsten carbide synthesis in an inert copper matrix was analyzed. It was demonstrated that the milling duration is a critical factor for creating the direct contacts between the W and C reactants and increasing the reactive transformation degree. A WC-W2C-Cu composite was fabricated from the W-C-3Cu powder mixture milled for 10 min and subjected to SPS at a temperature of 980 °C for 5 min. The formation of unconventional microstructures with Cu-rich regions is related to inter-particle melting during SPS. The WC-W2C-Cu composite showed a promising combination of mechanical and functional properties: a hardness of 300 HV, an electrical conductivity of 24% of the International Annealed Copper Standard, a residual porosity of less than 5%, a coefficient of friction in pair with a WC-6Co counterpart of 0.46, and a specific wear rate of the material of 0.52 × 10-5 mm3 N-1 m-1.

Effect of Sintering Temperature on the Thermoelectric Properties of Ag2Se Fabricated by Spark Plasma Sintering with High Compression

Silver selenide (Ag2Se) is a high‐performance thermoelectric (TE) material near room temperature. This research improves its TE figure‐of‐merit (ZT) by varying the sintering temperatures (423–723 K) in the spark plasma sintering (SPS) process with high compression pressure (300 MPa). The SPS compaction of Ag2Se powders synthesized by wet chemical reaction leads to the fast fusion of particles so that the grain boundaries are hardly visible. Furthermore, the fast fusion causes nanopores at the grain surface and some cracks, particularly at higher sintering temperatures. These featured microstructures decrease carrier concentrations and affect the TE properties significantly. The TE measurements show that increasing sintering temperatures results in decreased electrical conductivity and increased magnitude of the Seebeck coefficient due to microstructural defects. Increasing SPS temperatures also suppresses the thermal conductivity from enhancing phonon scattering by defects. The bulk Ag2Se sample sintered at 723 K shows the best TE performance with the maximum ZT of 0.90 with a slight variation from 300 to 400 K. Thus, the high‐temperature SPS with high‐compression pressure is likely to be the key for fabricating bulk Ag2Se with high TE performance.

Preparing and Wear-Resisting Property of Al2O3/Cu Composite Material Enhanced Using Novel In Situ Generated Al2O3 Nanoparticles.

Al2O3/Cu composite material (ACCM) are highly suitable for various advanced applications owing to its excellent properties. In the present work, a combination of the solution combustion synthesis and hydrogen reduction method was first employed to prepare Al2O3/Cu composite powder (ACCP), and subsequently ACCM was prepared by employing spark plasma sintering (SPS) technique. The effect of Al2O3 contents and SPS temperatures on the properties (relative density, hardness, friction coefficient, and electrical conductivity, et al.) of ACCM were investigated in detail. The results indicated that ACCM was very dense, and microstructure was consisted of fine Al2O3 particles evenly distributed in the Cu matrix. With the increase of SPS temperature, the relative density and hardness of ACCM had first increased and then decreased. At 775 °C, the relative density and hardness had attained the maximum values of 98.19% and 121.4 HV, respectively. With the increase of Al2O3 content, although the relative density of ACCM had gradually decreased, nevertheless, its friction coefficient had increased. Moreover, with the increase of Al2O3 contents, the hardness of ACCM first increased and then decreased, and reached the maximum value (121.4 HV) with 3 wt.% addition. On the contrary, the wear rate of ACCM had first decreased and then increased with the increase of Al2O3 contents, and attained the minimum (2.32 × 10-5 mm3/(N.m)) with 3 wt.% addition.

Effect of spark plasma sintering temperature on the multi-scale microstructure evolution and mechanical properties of Ti2AlC/TiAl composites with network architecture

In the present work, Ti2AlC/TiAl composites with network architecture were fabricated by the method of spark plasma sintering (SPS) at different temperature using Ti–48Al–2Cr–2Nb pre-alloyed powders and graphene nanosheets (GNSs) as raw materials. The effect of sintering temperature on the multi-scale microstructure evolution and mechanical properties of Ti2AlC/TiAl composites with network architecture was investigated. The results showed that equiaxed γ-TiAl matrix composite reinforced with the continuous network structured micro-Ti2AlC phases could be in-situ fabricated at the sintering temperature of 1200 °C. With the increase of sintering temperature from 1200 °C to 1320 °C, the micro-Ti2AlC continuous network structure gradually transforms into the nearly continuous, quasi-continuous and semi-continuous network. While the equiaxed γ-TiAl matrix gradually transforms into duplex, nearly lamellar, fully lamellar TiAl. Meanwhile, the micro-nano Ti2AlC precipitates would be formed in the TiAl matrix when the sintering temperature exceeds 1200 °C. When the sintering temperature is 1310 °C, the near lamellar TiAl matrix composite reinforced with the quasi-continuous network structured micro-Ti2AlC phases and micro-nano Ti2AlC precipitates is obtained, and the as-prepared composite possesses the best mechanical properties at both room and high temperature due to the synthetic effect of quasi-continuous network structure, intrinsic properties of Ti2AlC and lamellar TiAl.

A relationship of porosity and mechanical properties of spark plasma sintered scandia stabilized zirconia thermal barrier coating

Porous ceramic materials are popularly accepted as thermal barrier coatings (TBCs) in insulating gas turbine parts working at high temperatures. In this research, three different types of Scandia stabilized zirconia (ScSZ) systems, a nanometric 10 mol% ScSZ (10-ScSZ), a micrometric 8 mol% ScSZ (8-ScSZ) and a combination of these two powders (10-8-ScSZ) have been developed by Spark Plasma Sintering (SPS) process. Varying SPS parameters, for instance, temperature, pressure and dwell time were applied to develop the different volumes of porosity in the materials. Subsequently, the microstructure of the materials has been studied and mechanical properties have been evaluated. All three materials demonstrate a reduced porosity level at high sintering temperature and pressure. However, the nanometric 10-ScSZ material shows a higher reduction of porosity from 51.8% to 11.1% at 30 MPa pressure and 40.2%–8.5% at 60 MPa pressure within the temperature range of 1000–1200 °C. Besides, the 10-8-ScSZ composite exhibits substantially increased porosity in comparison to its constituent parts. The results also show that the nanometric 10-ScSZ material exhibits a greater mechanical strength including Vickers microhardness of 81 HV, flexural strength of 361 MPa and elastic modulus of 187 GPa at 5% porosity level, as compared to the other two materials. Additionally, it is observed that all the mechanical properties for all three materials consistently decrease with the increase in porosity levels. While compared with the traditional atmospheric plasma spray (APS) processed ceramic coating, the porous ScSZ coating materials exhibit a larger elastic modulus. Therefore, the porous ScSZ developed by the SPS process could be a prospective alternative thermal barrier coating (TBC).

Densification of the eggshell powder by spark plasma sintering

Chicken eggshells (eggshells) are the bio-waste produced during day-to-day egg consumption by humans. The eggshell contains calcium carbonate (CaCO3) along with several other elements such as Si, Mg, K, P, Na, etc., which enables its application for human bio-implants. Our research work aims to practically implement the eggshell powder as the bio-implant, for which, the study of the densification behavior of the eggshell powder is required. Hence, the present paper represents the densification behavior of the crystalline eggshell powder by spark plasma sintering. The eggshell powders were irregular in shape with a wide particle size distribution. The eggshell powder was sintered at six varying temperatures, i.e., 250 °C, 500 °C, 750 °C, 850 °C, 900 °C, and 1000 °C. The consolidated samples were characterized through SEM, FTIR, and XRD analysis, and the optimum spark plasma sintering temperature was determined. The consolidation of eggshells at 850 °C not only avoids the calcination process (due to the application of pressure) but gives optimum density and hardness making it an optimum condition for consolidating eggshells into compacts.

Patterns of the Effect of the Temperature of Spark Plasma Sintering on the Microstructure of Thermoelectric Composites Based on the Matrix of Bi2Te2.1Se0.9Bi2 with Cobalt Inclusions

Patterns of the Effect of the Temperature of Spark Plasma Sintering on the Microstructure of Thermoelectric Composites Based on the Matrix of Bi2Te2.1Se0.9Bi2 with Cobalt Inclusions