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Self-Reinforced Nitrogen-Rich Calcium–α-SiAlON Ceramics

Authors


  • P. Becher—contributing editor

  • S. Esmaeilzaeh possesses a research fellowship from the Royal Swedish Academy of Sciences financed by the Knut and Alice Wallenberg Foundation. The Swedish Research Council is acknowledged for financial support.

†Author to whom correspondence should be addressed. e-mail: zaida@inorg.su.se

Abstract

Nitrogen-rich Ca–α-SiAlON ceramics with nominal compositions CaxSi12−2xAl2xN16 and 0.2≤x≤2.6, extending along the Si3N4–1/2Ca3N2:3AlN tie line, were prepared from Si3N4, AlN, and CaH2 precursors by hot pressing at 1800°C. The x values attained were determined by energy-dispersive X-ray (EDX) microanalysis and X-ray powder diffraction (XRPD) data using the Rietveld method. The results show that Ca–α-SiAlONs form continuously within the compositional range x=0 to at least x=1.82. Phase assemblages, lattice parameters, Vickers hardness, and fracture toughness were determined and correlated to the calcium content, x. Owing to a high sintering temperature and the use of CaH2 as a precursor, grain growth was kinetically enhanced, resulting in self-reinforced microstructures with elongated grains. The obtained Ca–α-SiAlON ceramics demonstrate a combination of both high hardness ∼21 GPa, and high fracture toughness ∼5.5 MPa·m1/2.

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