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

Nitrogen‐rich Ca–α‐SiAlON ceramics with nominal compositions Ca x Si 12−2 x Al 2 x N 16 and 0.2≤ x ≤2.6, extending along the Si 3 N 4 –1/2Ca 3 N 2 :3AlN tie line, were prepared from Si 3 N 4 , AlN, and CaH 2 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 CaH 2 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·m 1/2 .