Papers by Keyword: Spark Plasma Sintering (SPS)

Abstract: Powder metallurgy (P/M) titanium matrix composite (TMC) reinforced with multi-wall carbon nanotube (MWCNT) was prepared by spark plasma sintering (SPS) and hot extrusion process, where the powder surface was coated by un-bundled CNTs via wet process. The microstructure and mechanical properties of P/M pure titanium and reinforced with CNTs were evaluated. The distribution of CNTs and in-situ formed titanium carbide (TiC) compounds during sintering was investigated by optical and scanning electron microscopy (SEM) equipped with EDS analyser. The mechanical properties of TMC were significantly improved by adding a small amount of CNTs. For example, when employing the pure titanium composite powder coated with CNTs of 0.35 mass%, the increase of tensile strength and yield stress of the extruded TMC was 157 MPa and 169 MPa, respectively, compared to those of extruded titanium materials with no CNT additive. Fractured surfaces of specimens were analysed by SEM, and the uniform distribution of CNTs and TiC particles, being effective for the dispersion strengthening, at the surface of the TMC were obviously observed.

Abstract: Different compositions of α- and α-/β- SiAlON materials have been prepared from separate nanopowders and their composites: Si3N4 – AlN, Si3N4, Al2O3 and Y2O3, produced by the method of plasma-chemical synthesis. Compositions have been sintered by spark plasma sintering (SPS) method in vacuum at 1700 °C with a heating rate of 100 °C/min and holding time of 5 min. The densification behaviour of the materials at these sintering conditions depends insignificantly on the powder composition. It is possible to obtain dense ceramic materials with relatively fine-grained structure (200-400 nm) and good mechanical properties from nanosized powders at relatively low temperatures (1400-1600 °C). The holding time at applied compacting conditions is still too short to ensure the formation of α- SiAlON phase corresponding to the phase diagram. All samples consist of β- SiAlON’s of differing composition and this is the reason for relatively low hardness of samples (HV5 = 15,6-16,9 GPa).

Abstract: Carbon nanotubes reinforced alumina was fabricated by spark plasma sintering method. When adding 0.2wt% nanotubes, the fracture toughness of the composites prepared increases 19% compared with the pure alumina ceramics. The effect of sintering schedule on microstructure and mechanical properties is investigated systematically. Microstructure studies reveal that at high sintering temperature, the nanotubes tend to gather in the gaps surrounded by three or more grains in a flocculent state, which leads to poor mechanical properties. Raman spectrum indicates that long sintering duration may cause serious nanotubes destruction and lower the mechanical properties.

Abstract: Powder metallurgy (PM) method to fabricate 6.5% silicon steel attracts much attention due to the lower energy consumption and cost. In this paper, Fe-6.5%Si alloy was prepared by spark plasma sintering (SPS) from the mixture of Fe and FeSi powders with different size. The sintering process was investigated through the shrinkage behavior, phase change and microstructure. The results show that the shrinkage starts from 500°C, lower than conventional sintering methods. The sintering temperature and FeSi powder size influence the reaction between Fe and FeSi.

Abstract: The purpose of this study was to investigate the oxidation of ZrB2/ZrO2 (ZZ) and ZrB2/ZrO2/SiC (ZZS) ceramics. The ceramics were fabricated by spark plasma sintering (SPS) at 1900°C and exposed to ten-minute oxidation cycles in stagnant air at 1200°C in a box furnace with molybdenum disilicide heating elements. Results of relative density, surface phase change and the rate of weight growth show that the addition of ZrO2 improved the sintering properties of ZrB2 ceramics. While the resistance to oxidation declined with the increase content of ZrO2. And the addition of SiC improved the resistance to oxidation of ZrB2/ZrO2 composites significantly.

Abstract: The single phase of Bi-doped Mg2Si0.5Sn0.5 compounds have been successfully fabricated by solid state reaction-spark plasma sintering (SPS). The effect of Bi doping concentration on the thermoelectric properties of Mg2Si0.5Sn0.5 is mainly investigated. The doping of Bi atom introduces impurity energy to Mg2Si0.5Sn0.5 compounds, which results in the increase of carrier concentration ( ), meanwhile it causes the increase of crystal distortion, enhancing the scatter of phonon. The results show that with the increasing of Bi doping content, the electrical conductivity (σ) increase, the absolute Seebeck coefficient ( ) and thermal conductivity ( ) decrease slightly in the measuring temperature range between 300 K and 800K. When the doping concentration of Bi is up to 2.5at% (nominal molar percent), the sample shows a maximum value of the figure of merit, ZT, is 0.78 at 800K.

Abstract: A group of boron-carbon ceramic material was in-situ synthesized and densified simultaneously via Spark Plasma Sintering (SPS) technique from carbon and boron element powders with different molar ratio. The phase structures of samples with different B/C molar ratio were characterized by X-ray Diffraction (XRD). The B/C atomic ratio of the sintered materials was calculated from X-ray photoelectron spectroscopy (XPS) measurement data. Meanwhile, the chemical analysis (CA) method had also been taken to verify the B/C atomic ratio. Finally, the experience equation had been obtained to control the B/C atomic ratio of sintered samples.

Abstract: Nanocomposites and heavy doping both are regarded as effective way to improve materials’ thermoelectric properties. 0.7at% Bi-doped Mg2Si nanocomposites were prepared by spark plasma sintering. Results of thermoelectric properties tests show that the doping of Bi atom effectively improves the electrical conductivity of Mg2Si，and the nanocomposite structures are helpful to reduce thermal conductivity and increase Seebeck coefficient, hence improving the thermoelectric performance. A maximum dimensionless figure of merit of 0.8 is obtained for the Bi-doped Mg2Si nanocomposite with 50 wt % nanopowder inclusions at 823K, about 63% higher than that of Bi-doped Mg2Si sample without nanopowder inclusions and 119% higher than that of microsized Mg2Si sample without Bi-doped, respectively.

Abstract: Ti-45Al-2Cr-2Nb-1B-0.5Ta (at.%) bulk alloys with dense and ultrafine grains were fabricated by Double Mechanical Milling (mechanical milling + heat treatment + mechanical milling) and spark plasma sintering method. The phase composition and microstructure of the milled powder and bulk alloy sintered by SPS at different temperature (900oC, 1000oC and 1100oC), and the relationship between microstructure and properties of bulk alloys were investigated. The results demonstrate that high-quality composite powders (low contaminant, size uniform distribution and elements homogeneous dispersion) can be obtained by double mechanical milling. The composite powders prepared by primary mechanical milling were uniform and partially solid solution. Ti3Al、Ti、Al3Ti and TiAl phases were found after heat treatment while Al phase disappeared. The fined grain size and particle size were achieved by subsequent mechanical milling. The whole mechanical milling leads to alloying and the refined grain and particle, which also cause lattice distortion and powders system energy increased. SPS results showed that the densified and ultrafine grained Ti-45Al-2Cr-2Nb-1B-0.5Ta alloy is mainly consisted of TiAl, Ti3Al phase and a small quantity of TiB2 phase. With the increasing of sintering temperature, grain size of TiAl based alloy increase. The mechanical properties depend on microstructure and grain size. The relationship between compression properties, bending properties and microstructure was discussed.

Abstract: SiGe alloy composite material including TiN nanoparticle were prepared. The TiN nanoparticles as the inert scattering center were fabricated by Nitrogen plasma-metal reaction. The sintered samples were characterized by electrical resistivity and seebeck coefficient measurement. Adding nanophase inclusion into the SiGe alloy matrix, the Seebeck coefficient increased, the electrical conductivity decreased and the electrical power factor only slightly reduced.