Spark Plasma Sintering Temperature Research Articles

Phase formation at the Ti<sub>2</sub>AlN under the spark-plasma sintering in the Ti/AlN system

The synthesis of the Ti2AlN-based material by means of the mechanical activation (MA) of the Ti‒AlN powder mixture in the planetary mill followed by the vacuum spark-plasma sintering (SPS). It was shown that the phase ratio AlN/Ti gradually decreases under mechanical activation. The data are given on the sample's phase composition, density and hardness after the SPS. The maximum Ti2AlN content value of 90 mass percent was achieved at the SPS temperature 1300 °C. The samples had the lowest porosity value of 1,9 % at the SPS temperature 1200‒1300 °C, the HV0,5hardness being close to 7 GPa.

Highly-porous hierarchical SiC structures obtained by filament printing and partial sintering

Three-dimensional (3D) porous silicon carbide (SiC) structures with total porosity in the range of 64–85% are achieved from nanosized SiC powders by filament printing and partial sintering in a spark plasma sintering (SPS) furnace. The effects of the SPS temperature (1500 and 1700 °C) and the addition of oxide sintering aids (7 wt. % Y2O3+Al2O3) on the porosity of the scaffolds are quantitatively compared. More specifically, hierarchical porosity consisting of meso-pores (< 50 nm) in the struts and open macro-pores (in the range of 500–700 μm) defined by the patterned structure is verified for the 1500 °C SPS treatment. The strength of the structures as a function of the density as well as their cooling profiles, once subjected to rapid heating under a direct flame, are analyzed. By following this easy route, an adaptable family of robust light 3D SiC structures with hierarchical porosity is accomplished.

Evaluation of Thermal, Fracture, and High Temperature Behavior of Mechanically Alloyed and Spark Plasma Sintered Nano-Y2O3 Dispersed W-Ni-Mo and W-Ni-Ti-Nb Alloys

Abstract Tungsten (W), Nickel (Ni), Molybdenum (Mo), Niobium (Nb), Titanium (Ti) based W-Ni-Mo and W-Ni-Ti-Nb alloys with nano-yttrium oxide (Y2O3) dispersion and nominal compositions of W79Ni10Mo10(Y2O3)1 (Alloy A) and W74Ni10Ti5Nb10(Y2O3)1 (Alloy B) (all in weight percent) were fabricated by mechanical alloying and spark plasma sintering (SPS) at 1,000°C, 1,200°C, and 1,400°C for 5 min with 75 MPa pressure. The thermal behavior of milled powders and microstructure evolution of milled and consolidated products were examined by scanning electron microscopy, energy-dispersive spectroscopy, and high-resolution transmission electron microscopy. The activation energy of recrystallization for Alloy B is higher as compared to the recently investigated oxide dispersion-strengthened tungsten alloys. The mode of fracture is predominantly intergranular with a titanium addition. Alloy A SPS at 1,400°C shows superior oxidation resistance at 1,000°C as compared to Alloy B at the identical SPS temperature (1,400°C), owing to a higher intensity of the protective nickel tungsten tetroxide, yttrium tungstate oxide scale formation, and less variation in the molar volume of formed oxides.

Advanced synthesis of highly crystallized hexagonal boron nitride by coupling polymer-derived ceramics and spark plasma sintering processes—influence of the crystallization promoter and sintering temperature

Hexagonal boron nitride nanosheets (BNNSs) are promising 2D materials due to their exceptional chemical and thermal stabilities together with their electrical insulation properties. A combined synthesis method involving the polymer-derived ceramics (PDCs) route and the spark plasma sintering (SPS) process is proposed, leading to well-crystallized and pure layered h-BN crystals, prone to be exfoliated into large BNNSs. Here we focus more specifically on the influence of two key parameters of the process to be optimized: the Li3N concentration (0–10 wt%) and the SPS temperature (1200 °C–1950 °C). The presence of Li3N, added as crystal promoter in the pre-ceramic powder, significantly improves the crystallinity level of the product, as evidenced by XRD, SEM and Raman spectrometry. SPS temperature strongly modifies the size of the resulting h-BN flakes. The influence of SPS temperature on both purity and crystallinity is studied using cathodoluminescence. h-BN flakes larger than 200 μm2 (average flake area) are obtained. Few-layered BNNSs are successfully isolated, through exfoliation process.

Impact of mechanical activation on sintering kinetics and mechanical properties of ultrafine-grained 95W-Ni-Fe tungsten heavy alloys

This paper is a study of sintering mechanisms, structure, and mechanical properties of ultrafine-grained 95W-Ni-Fe tungsten heavy alloys. Powder particle sizes were controlled by mechanical activation (MA) of original coarse-grained components and by addition of ultrafine particles. W-Ni-Fe alloys were obtained by sintering in hydrogen and Spark Plasma Sintering (SPS) in a vacuum. The dependence of ultrafine-grained (UFG) alloy density on sintering temperatures has been found to be non-monotonic with a maximum corresponding to the optimal sintering temperature. It has been demonstrated that the sintering activation energy of UFG alloys is significantly lower than that of coarse-grained alloys. It has been shown that the optimal SPS temperature for mechanically activated nanopowders goes down by 350–400 °C in comparison with the optimal sintering temperature in hydrogen for coarse-grained 95W-Ni-Fe powder composition. The reason for a lower optimal sintering temperature lies in a decreased activation energy of grain-boundary diffusion and formation of a non-equilibrium solid solution of nickel and iron in the surface layer of tungsten α-W particles during high-energy MA. High-energy MA and SPS were used to obtain samples of UFG tungsten alloys with high mechanical properties: macro-elastic limit – up to 2250 MPa, yield stress – up to 2500 MPa.

Influence of sintering temperature and pressure on the 3C-6H transition of silicon carbide

The influence of Spark Plasma Sintering pressure and temperature on the evolution of the phase composition of two sources of β-SiC ceramic were studied based on X-ray diffraction and Raman scattering measurements. A commercial powder and a powder derived from a preceramic polymer precursor were chosen, and the investigation was undertaken in the [1850-2200 °C] temperature range and in the [17–127 MPa] pressure range. Analyses revealed that the 3C-6H phase transition depends on sintering pressure, which is shown to stabilize the cubic phase. The stability domains of the cubic phase as a function of sintering P and T were determined for both powdery precursors and revealed that the cubic phase stability is also linked to the nature of powdery precursor and in particular to its crystallinity state. The improvement of cubic phase stability at higher temperature by applying pressure allows sintering β-SiC ceramic with high density.

Effects of sintering temperature on the microstructure and thermoelectric properties of mesostructured Co4Sb11.5Te0.5 skutterudites dispersed nano-TiN

The mesostructured skutterudites Co4Sb11.5Te0.5 + nano-TiN composites are prepared through ball milling and spark plasma sintering (SPS). The influence of the various SPS temperatures within the range of 813–933 K on the microstructure and thermoelectric properties are focus in this work. The average grain sizes of the skutterudites increase from ~ 110 to ~ 500 nm with the increasing SPS temperature, while the densities of composites decrease from 7.02 to 6.26 g cm−3. Additionally, the phase of CoTe2 is detected in the samples sintered at 903–933 K. With the SPS temperature increasing from 813 to 903 K, the electrical conductivity and thermal conductivity increase simultaneously, and then decrease when SPS temperature rises to 933 K. The absolute value of Seebeck coefficient shows no clear changes when SPS temperature is not higher than 873 K but then slightly decreases with the increasing of SPS temperature. At last, the optimum SPS temperature is determined as 873 K, the ZT value of 1.07 at 800 K for the sample SPSed at 873 K is obtained, which is 11.5% higher than that of the sample SPSed at 903 K.

Densification kinetics of boron carbide with medium entropy alloy as a sintering aid during spark plasma sintering

AbstractThe high sintering temperature of pure B4C considerably limits its widespread application, thus searching an effective sintering aid is critical. In this work, B4C‐based ceramic with 1 vol.% nonequiatomic Fe50Mn30Co10Cr10 medium entropy alloy as a sintering aid were fabricated at 1900‐2000°C by spark plasma sintering (SPS) under applied pressure, and their mechanical properties were examined and compared with pure B4C ceramic sintered at same condition. The maximal flexural strength of 255.59 MPa, microhardness of 2297.6 Hv0.2 and fracture toughness of 3.62 MPa m1/2 could be obtained at optimized SPS pressure of 50 MPa, which were all higher than those of pure B4C ceramic. To better understand the densification kinetics mechanisms, the densification ratio as a function of SPS temperature and pressure was theoretically analyzed using steady creep model. It was found that densification controlled by grain‐boundary sliding at lower pressure transferred to power law creep regime at higher pressure, which were proved by the dislocation net shown in transmission electron microscopy image.

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.

Synthesis and 3D Interconnected Nanostructured h-BN-Based Biocomposites by Low-Temperature Plasma Sintering: Bone Regeneration Applications

Recent advances and demands in biomedical applications drive a large amount of research to synthesize easily scalable low-density, high-strength, and wear-resistant biomaterials. The chemical inertness with low density combined with high strength makes h-BN one of the promising materials for such application. In this work, three-dimensional hexagonal boron nitride (h-BN) interconnected with boron trioxide (B2O3) was prepared by easily scalable and energy efficient spark plasma sintering (SPS) process. The composite structure shows significant densification (1.6–1.9 g/cm3) and high surface area (0.97–14.5 m2/g) at an extremely low SPS temperature of 250 °C. A high compressive strength of 291 MPa with a reasonably good wear resistance was obtained for the composite structure. The formation of strong covalent bonds between h-BN and B2O3 was formulated and established by molecular dynamics simulation. The composite showed significant effect on cell viability/proliferation. It shows a high mineralized nodule formation over the control, which suggests its use as a possible osteogenic agent in bone formation.

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.

3D-Printed Fe-doped silicon carbide monolithic catalysts for wet peroxide oxidation processes

The catalyst stability has become a key issue for wet peroxide oxidation (CWPO) processes. Herein, an alternative method for the manufacturing of iron (Fe) catalysts by using three-dimensional (3D) printing techniques is proposed to enhance the Fe immobilization, where these metallic nanoparticles are part of a printable aqueous silicon carbide (SiC)-based ink. Cylindrical Fe/SiC monoliths (D ∼ 13 mm, H ∼ 4.5 mm, 74 squared cells cm−2) are manufactured by direct ink writing (Robocasting) and further treatment up to 1500 °C into a spark plasma sintering (SPS) furnace to assure a certain mechanical integrity. It was found that the increasing SPS temperature progressively decreases the porosity -or increases the apparent density- of the printed struts, lowering the accessibility of reactants to the Fe sites but improving the catalyst mechanical strength and leaching resistance. 3D Fe/SiC monoliths treated at 1200 °C arise as robust catalysts for CWPO processes due to the combination of good catalytic activity, highly- efficient H2O2 decomposition, long-term stability and excellent mechanical strength. A simple potential kinetic model is proposed, capable of describing the phenol disappearance, TOC removal and H2O2 consumption. The results of this study point out a new approach for the conformation by Robocasting of metal-based catalysts in suitable morphological 3D-structures for scaling-up reactions.

Spark Plasma Sintering of fine-grain ceramic-metal composites based on garnet-structure oxide Y2.5Nd0.5Al5O12 for inert matrix fuel

Using wet chemistry techniques, ultrafine powders of complex oxides Y2.5Nd0.5Al5O12 (YAG) have been obtained with the garnet structure and coated with layers of nickel by means of precipitation from salt solutions. Spark Plasma Sintering (SPS) was used to obtain fine-grain ceramic composites YAG – Ni with 92–99% density. Sintering activation energies were determined and it was demonstrated that the intensity of high-rate sintering of the investigated ceramic composites is determined by the intensity of the nickel creep at lower heating temperatures, the intensity of oxygen diffusion in the garnet crystal lattice at average SPS temperatures, and the intensity of grain boundary diffusion at high SPS temperatures.

Mechanical Properties of Bulk MgB2 Superconductors Processed by Spark Plasma Sintering at Various Temperatures

In order to improve the mechanical properties of bulk MgB2 superconductor, high packing ratio bulk samples were processed by spark plasma sintering (SPS) at various temperatures. Effects of the SPS temperature on the mechanical properties of the bulk MgB2 superconductor are investigated through bending tests of specimens cut from the bulk samples. Both Young's modulus and bending strength were improved by the increase in the SPS temperature. The improvements of the mechanical properties are mainly due to the improvement in the packing ratio. The relationships between the bending strength and packing ratio of the spark plasma sintered bulk samples are similar to those of other bulk MgB2 pieces processed by capsule method and hot isostatic pressing.

Densification improvement of spark plasma sintered TiB2-based composites with micron-, submicron- and nano-sized SiC particulates

Taguchi design of experiments methodology was used to determine the most influential spark plasma sintering (SPS) parameters on densification of TiB2–SiC ceramic composites. In this case, four processing factors (SPS temperature, soaking time, applied external pressure and SiC particle size) at three levels were examined in order to acquire the optimum conditions. The statistical analysis identified the sintering temperature as the most effective factor influencing the relative density of TiB2–SiC ceramics. A relative density of 99.5% was achieved at the optimal SPS conditions; i.e. temperature of 1800 °C, soaking time of 15 min and pressure of 30 MPa by adding 200-nm SiC particulates to the TiB2 matrix. The experimental measurements and predicted values for the relative density of composite fabricated at the optimum SPS conditions and reinforced with the proper SiC particle size were almost similar. The mechanisms of sintering and densification of spark plasma sintered TiB2–SiC composites were discussed in details.

A statistical approach towards processing optimization of ZrB2–SiC–graphite nanocomposites. Part I: Relative density

The influence of sintering variables and nano-graphite addition on the densification behavior of ZrB2–SiC based ceramics has been investigated. The ZrB2 matrices, reinforced with 25 vol% submicron SiC particles and 0–10 wt% graphite nano-flakes, were fabricated by spark plasma sintering (SPS). The Taguchi design of experiment approach was employed to study the effects of SPS variables (temperature, dwell time, and pressure) and nano-graphite content. Statistical analysis of variance identified the SPS temperature and graphite content as the most influential parameters affecting the relative density of as-sintered ceramics, whereas the SPS pressure did not have an obvious impact on the densification process. The thermodynamical and microstructural analyses showed that the addition of graphite nano-flakes led to the removal of the thin oxide layers from the surfaces of the non-oxide starting materials. The elimination of such harmful oxides and the in-situ formation of nano-sized ZrC and B4C phases resulted in the enhancement of sinterability of ZrB2–SiC–graphite nanocomposites. A fully dense sample was achieved at optimal processing conditions; i.e. by sintering at 1900 °C for 7 min under 40 MPa and adding 5 wt% graphite nano-flakes.

Preparation and Characterization of Mechanical Properties of Hydroxyapatite/Carbon Nanotube Laminated Ceramic Composites Consolidated by Spark Plasma Sintering

Laminated xCNTs-HAP/yCNTs-HAP ceramic composites were consolidated using a spark plasma sintering(SPS) technique at SPS temperature 900°C, pressure 40MPa and holding time 5min. The effect of carbon nanotubes content and thickness of each layer on mechanical properties of the composites was investigated. It was demonstrated that the stratified structure improvedthe flexural strength obviously. All the flexural strength of laminar compositewashigher than that of single CNTs-HAP ceramic, up to 112.4MPa. Since the matrix of each layer wereHAP, the difference liesonly in the content of carbon nanotubes, thus avoiding the common problem of the interlayer bonding in other layered composites with different materials. In order to characterize the toughness of the layered composite, the stress-strain curve was compared showingthat the existence of the stratified structure improved the stress-strain obviously.

Fabrication of Titanium-Niobium-Zirconium-Tantalium Alloy (TNZT) Bioimplant Components with Controllable Porosity by Spark Plasma Sintering.

Spark Plasma Sintering (SPS) is used to fabricate Titanium-Niobium-Zirconium-Tantalum alloy (TNZT) powder—based bioimplant components with controllable porosity. The developed densification maps show the effects of final SPS temperature, pressure, holding time, and initial particle size on final sample relative density. Correlations between the final sample density and mechanical properties of the fabricated TNZT components are also investigated and microstructural analysis of the processed material is conducted. A densification model is proposed and used to calculate the TNZT alloy creep activation energy. The obtained experimental data can be utilized for the optimized fabrication of TNZT components with specific microstructural and mechanical properties suitable for biomedical applications.

Synthesis and Characterization of Aluminium Base in situ Metal Matrix Composites by Spark Plasma Sintering

Fe-aluminide and alumina reinforced in-situ aluminium based metal matrix composite was prepared by spark plasma sintering (SPS) of aluminium and nanosized Fe2O3 powder mixture. In-situ reinforcements were formed during SPS by exothermal reaction between aluminium and nano-size Fe2O3 particle. The thermal characteristics of the in-situ reaction were studied by differential scanning calorimetry (DSC). Field Emission Scanning Electron Microscopy (FESEM) along with the Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD) techniques were used to study the microstructural architecture of the composites as a function of SPS temperature and the volume fraction of reinforcement. Microhardness measurement of the composite shows significant increase in hardness with increase in SPS temperature and volume fraction of secondary phase.

Distribution of carbon contamination in oxide ceramics occurring during spark-plasma-sintering (SPS) processing: II - Effect of SPS and loading temperatures

Carbon contamination during the SPS processing was investigated in the spinel, alumina and zirconia. The carbon contamination changes with the SPS conditions and the target materials. At the high heating rate of 100 °C/min, the contamination occurred over the entire area in the spinel, but only around the surface areas in the alumina and zirconia. For the spinel, the contamination is sensitive to the SPS parameters, such as the heating rate and loading conditions, but less sensitive to the sintering temperature. This suggests that the carbon contamination was caused by evaporation of CO gas from the carbon paper/dies. At the high heating rates, the carbon evaporation is enhanced due to the rapid heating, and then, the evaporated CO gases are encapsulated into the closed pores during the heating process and remain in the matrix. The carbon contamination can be suppressed by a high temperature loading even at the high heating rate.