High-Temperature Creep and Fracture of β′Si₃N₄ Ceramic Alloys

Abstract

The simultaneous substitution of Al³⁺ and O^2- for Si⁴⁺ and N³⁻, respectively, in the β′Si₃N₄ crystal structure produces a solid solution’ (β′) phase Si_3−x Al_x O_x N_4−x which is the basis for a range of engineering ceramics. These ceramic ‘alloys’ may approach the mono-phase state^l or be‘composites’ of β′ with a matrix phase which is the residue of a liquid-sintering aid.^{2, 3} Typically, the substitution level x is less than 0.5 and there is little change in the intrinsic properties of the β Si₃N₄ crystal. However, it is the indirect influence of crystal substitution on the volume and composition of the residual phase which has a dominant influence on ceramic properties, especially at elevated temperatures.