High‐Temperature Strength of Sinter‐Forged Silicon Nitride with Lutetia Additive

A sinter‐forging technique was successfully applied to fabricate a silicon nitride with a lutetia (Lu 2 O 3 ) additive. The sinter‐forged specimen had a strongly anisotropic microstructure where rodlike silicon nitride grains preferentially aligned perpendicular to the forging direction. The specimen exhibited superior strength of ∼700 MPa at 1500°C. This strength was highest when compared with previous silicon nitrides at temperatures >1400°C. Such superior high‐temperature strength was attributed to grain alignment as well as to the refractory grain‐boundary glassy phase and the existence of glass‐free grain boundaries.