Additive-free hot-pressed silicon carbide ceramics-A material with exceptional mechanical properties

Additive-free hot-pressed silicon carbide ceramics-A material with exceptional mechanical properties

P. Šajgalík, J. Sedláček, Z. Lenčéš, J. Dusza, H.-T. Lin

Abstract

Densification of silicon carbide without any sintering aids by hot-pressing and rapid hot pressing was investigated. Full density (>99% t.d.) has been reached at 1850 °C, a temperature of at least 150–200 °C lower compared to the up to now known solid state sintered silicon carbide powders. Silicon carbide was freeze granulated and heat treated prior the densification. Evolution of microstructure, mechanical properties and creep behavior were evaluated and compared to reference ceramics from as received silicon carbide powder as well as those of commercial one. Novel method results in dense ceramics with Vickers hardness and indentation fracture toughness of 29.0 GPa and 5.25 MPa m1/2, respectively. Moreover, the creep rate of 3.8 × 10−9 s−1 at 1450 °C and the load of 100 MPa is comparable to the commercial α-SiC solid state sintered at 2150 °C.

Keywords

Silicon carbide, Hot pressing, Microstructure, Mechanical properties, Creep resistance, freeze granulation

Spark plasma sintering of zirconia/nano-nickel composites

Spark plasma sintering of zirconia/nano-nickel composites

Carlos F. Gutierrez-Gonzalez, Nestor W. Solis Pinargote, Said Agouram,
Pavel Y. Peretyagin, Sonia Lopez-Esteban and Ramon Torrecillas

Abstract
This work describes a whole processing route for obtaining dense and nanostructured zirconia-nickel composites with low contents of metallic phase (1–3.5 vol%). For the processing route, a combinationof spray-freezing and lyophilization has been proposed. After the calcination and reduction of the resultingpowders an X-ray and HRTEM characterization has been performed. This showed the formation of pure zirconia and nickel, well dispersed and homogeneously distributed, nanostructured phases. The obtainedpowders were subsequently sintered by Spark Plasma Sintering (SPS). As a result, dense ZrO2 Ni composites were obtained, revealing that the sizes of the metal particles were kept in the nanometer rangeand appear homogeneously and well dispersed into the ceramic matrix. The mechanical behavior of these materials was evaluated by means of the Vickers hardness, showing and increment of about 25% with
respect to pure zirconia with only a Ni concentration of 1 vol%.
Key words:
Spark plasma sintering, nanomaterials, nanocomposites, nanoceramics, powder materials, zirconia-nickel composites, mechanical properties.
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