High strength joints between silicon nitride parts - made using intermediate layer of hot pressed silicon nitride and alumina

摘要

Reaction-sintered and hot-pressed Si3N4 components are joined by a solid bond, achieved by using an intermediate layer (a) consisting of a powder mixt. of Si3N4 and AliO3, followed by hot pressing at below 1600 degrees C in a N2 atmos. to make the joint. The pref. powder mixt. consists of (a1) gamma-Al2O3 with size 1-100 nm; and (a2) Si3N4 with size 0.1-20 mu m, esp. using a molar ratio a1:a2 of between 10:90 and 70:30. Layer (a) is pref. applied by flame spraying; and hot pressing is pref. at 1500-1600 degrees C. Used e.g. for mfg. a gas turbine rotor, where a reaction-sintered component must be joined to a hot-pressed component, both being made of Si3N4, via a high strength joint.