Grain‐Boundary‐Phase Crystallization and Strength of Silicon Nitride Sintered with a YSlAlON Glass

Abstract

Densifying silicon nitride with a YSiAlON glass additive produced 99% dense materials by pressureless sintering. Subsequent heat‐treating led to nearly complete crystallization of the amorphous intergranular phase. Transmission electron microscopy revealed that for heat treatments at 1350°C, only β‐Y 2 Si 2 O 7 was crystallized at the grain boundaries. At a higher temperature of 1450°C, primarily YSiO 2 N and Y 4 Si 2 O 7 N 2 in addition to small amounts of Y 2 SiO 5 were present. Al existed only in high concentrations in residual amorphous phases, and in solid solution with Si 3 N 4 and some crystalline grain‐boundary phases. In four‐point flexure tests materials retained up to 73% of their strengths, with strengths of up to 426 MPa, at 1300°C. High‐strength retention was due to nearly complete crystallization of the intergranular phase, as well as to the high refractoriness of residual amorphous phases.