REFRACTORY OXYNITRIDE JOINTS IN SILICON-NITRIDE

Sintered silicon nitride was joined to itself by heating interlayers o f refractory oxide compositions above their liquidus temperatures in f lowing nitrogen. Only enough pressure was used to maintain alignment o f the parts in the fixture. The oxide compositions were in the Y2O3-Al 2O3-SiO2 and SrO-Al2O3-SiO2 families and the silicon nitride was from two commercial sources. Joined specimens were tested in four point fle xure from room temperature to 1300 degrees C. A maximum strength of 55 5 MPa was observed at 1000 degrees C, which as far as we know is the h ighest 1000 degrees C strength ever observed for silicon nitride joine d without high applied pressure. Quantitative measurements of composit ion profiles at the ceramic-oxide-ceramic interface revealed that inte rdiffusion of cations from the silicon nitride and the oxide joining m aterial maintains local charge balance. (C) 1998 Acta Metallurgica Inc .