Papers by Keyword: Spark Plasma Sintering (SPS)

Abstract: The high critical current density of YBCO-coated conductors prepared by rolling assisted biaxially textured substrate technic is mostly based on the high quality cube-textured substrates. In this paper, the effect of initial grain size of ingot on the microstructure and texture evolutions during cold rolling has been investigated in high alloyed Ni8W ingots, which can affect the cube texture formation in Ni8W alloy substrates subsequently. Finally, high quality cube texture had been obtained in Ni8W alloy substrate with fine initial grain size prepared by advanced SPS technology.

Abstract: Various solid state or ‘meltless’ recycling techniques have recently been developed for light metal scrap in form of chips. Main objective of all approaches is to bypass the need for remelting in order to reduce the overall required energy, and to avoid the material losses that occur during this step. Within this paper, the use of Spark Plasma Sintering (SPS) is proposed as a novel solid state recycling/welding technique for sheet metal scrap. Aluminium 5182 alloy scrap, derived from sheet metal, was successfully consolidated into a fully dense billet via SPS. The use of pulsed electric current heating, in temperatures well below the alloy melting point, combined with mechanical pressure, enchased the densification process resulting into a void-less material. The recycled SPS sample was fully densified and microstructural investigation has been performed in order to confirm effective oxide film breakage. The results illustrate the effectiveness of SPS in aluminium scrap consolidation, also in form of sheet scrap, providing additional means in solid state recycling. The involved mechanisms that contribute to oxide film fracture and scrap consolidation in SPS are being discussed.Keywords: Aluminium, recycling, spark plasma sintering (SPS)

Abstract: Use of spark plasma sintering (SPS) allows improving thermoelectric figure of merit Z of bulk nanothermoelectrics but required parameters of SPS process for achievement of best Z can be defined only empirically. In the present study the finite elements method for investigation of electric and thermal processes which occur in volume and on boundaries of sintering particles is applied. As a geometrical model a structural cell of a sintered sample, containing contact “a truncated cone - a plate” has been chosen. Temperature distributions in the volume of a sample depending on amplitude, on-off time ratio and duration of impact of the electric current has been obtained for solid solution based on bismuth telluride using the energy balance equation and the equation of electric current continuity. Under certain conditions nonlinear and nonlocal processes start to arise. The calculated temperature distributions at different sintering conditions were comparing with empirically defined experimental parameters that lead to improved value of Z. The comparison allows formulating recommendations to achieve best conditions of SPS process for increase of Z. The present method can be used for management of SPS fabrication process for different application, not only for thermoelectrics.

Abstract: K_0.5Na_0.5NbO₃ (KNN) was manufactured by spark plasma sintering (SPS), which is a fast sintering method allowing to control the grain growth. Different samples of KNN are sintered with SPS at 920°C under 50 MPa for 5 minutes. High densities over than 97% are achieved. In order to make domain engineering, KNN crystals are grown by floating zone method. Stable molten zone is reached when oxygen or nitrogen gas flux is used, leading up to 50 mm length of crystals. High electromechanical coupling factor kt about 46 %, kp around 45 % and ε33S/ε0 of 253 are achieved for KNN ceramics poled at optimum electric field about 3 kV / mm. KNN crystal boule exhibits kt about 40 % against 34 % for KNN ceramic, both poled at 1 kV / mm. These results are promising to replace PZT for transducers applications.

Abstract: The development of SiAlON-based ceramics has shown great impact in the field of cutting/drilling tool industry and other engineering applications. It is highly desirable to cut-down the cost of the cutting tools by increasing their service lifetime. Potential ways to improve tool life is by preparing these SiAlON-based ceramics adopting non-conventional synthesis routes and by using different precursors. The present study reports the results of synthesis of SiAlON-based nano-ceramics via spark plasma sintering (SPS) technique. Generally, metal nitride and metal oxide precursors are used for synthesizing self-reinforced SiAlON ceramics. In this work, nano-sized metallic precursors including amorphous-Si₃N₄ and crystalline β-Si₃N₄, SiO₂, AlN and Al₂O₃ were used, which could be a novel way to synthesize SiAlONs at low temperatures with enhanced performance. The properties of these SiAlONs are tailored by optimizing the synthesis parameters. The synthesized samples were characterized by X-ray diffraction and field emission scanning electron microscopy to study the effect of processing parameters on microstructure, density and hardness.

Abstract: Since FAST/SPS technology ensures an adequate and fast consolidation of different materials the demand for suitable pressing tool materials is growing. Graphite based materials are widely used and well known as FAST/SPS tool materials but they also have some unwanted or weak properties, for example, a possible reaction or reduction of sample material as well as low mechanical values compared to other tool materials. In this paper, an approach for the FAST/SPS consolidation of ZTA-Ti (C,N) and TiN-TiB₂ based cutting tool inserts in newly developed FAST/SPS tool materials which can be used for fully automated FAST2 devices is presented. Furthermore, a general strategy for the further development of FAST/SPS tool materials is focused.

Abstract: The consolidation of refractory ceramic powders at relatively milder conditions with respect to conventional methods represents an important target to achieve. Based on results recently reported in the literature, it is possible to state that the combination of the Self-propagating High-temperature Synthesis (SHS) with the Spark Plasma Sintering (SPS) technologies provides a useful contribution in this direction. Specifically, the two-steps processing route consisting in the synthesis of the ceramic powders by SHS and their subsequent densification by SPS is successfully utilized to obtain various dense MB₂-based materials (M= Zr, Hf, Ta). In this regard, an important role is played by the SHS process, particularly for the synthesis of composite powders. Indeed, stronger interfaces are established among the different phases formed in-situ, so that diffusion phenomena are promoted during SPS. Additional benefits are produced by the use of the latter technology, due to the direct passage of the electric current through the powders undergoing sintering and the die containing them.

Abstract: TiC interfacial layer is formed during titanium alloy to carbon steel diffusion bonding and prevents the formation of FeTi and Fe₂Ti intermetallic compounds, which have detrimental effect on the properties of joints. The TiC layer is extremely thermodynamically stable in contact with austenite and is formed at the steel/titanium interface even in the case when carbon content is about 0.1wt.%. The evolution of an initially formed interfacial titanium carbide layer includes its growth and simultaneously changing the composition of austenite (towards lower carbon content) and titanium (towards higher carbon content). The kinetics parameters of the interfacial layer growth (carbon diffusion coefficient and the activation energy) reflect the grain boundary mechanism of carbon diffusion through the interfacial layer with submicron grains microstructure.

Abstract: Tantalum diboride was synthesized and sintered from metallic tantalum powder and amorphous boron powder in one technological process using Spark Plasma Sintering method. The precursors were: tantalum with grain size below 5μm and boron with particle size in the range of 1-2μm. Tantalum powder, before mixing with boron, was subjected to high-energy milling under argon atmosphere in order to reduce specific surface area. The process should be carried out without air, due to protection against the influence of oxygen. During reactive sintering SPS process oxidation participation should be limited because of high exothermic reactions. Morphologies of the powders before and after milling were studied using SEM. Reactive sintering processes were carried out at temperatures from 1800°C up to 2200°C at 48MPa. Sintering duration was in the range of 1-30min. Volume changes of samples and temperature increase during the synthesis were observed and determined. The result of X-Ray phase composition analysis and microstructure observations using SEM are presented. Relative density, Young's modulus, Vickers hardness and fracture toughness of the materials were determined. During the reactive sintering the material of only one phase TaB₂, with high level of densification, was obtained.

Abstract: The characteristics and sinterability of the Al₂O₃-ZrO₂(Y₂O₃) nanoparticles produced by simple and effective microwave and molten salts methods and processed by using spark plasma sintering were studied and compared. The crystalline powders with the specific surface area in the range of 72–108 m²/g and crystallite size of 5–13 nm were obtained by calcination of samples prepared by both methods at 800 °C. The content of t-ZrO₂ phase depends on concentration of Al₂O₃, Y₂O₃ and on calcination temperature but the impact of the preparation method is insignificant. The phase transition of tetragonal ZrO₂ to monoclinic for the samples without Y₂O₃ started at 1000 °C though it was incomplete in the case of high content of Al₂O₃. The bulk materials with relative density of 86.1–98.7% were fabricated by the spark plasma sintering method at 1500–1600 °C depending on the content of Al₂O₃ and Y₂O₃.