Joining Si3N4-based ceramics with oxidation-formed surface layers

A simple processing technique has been developed for joining Si3N4,-based c eramics. Thin (<5 <mu>m thick), amorphous, or partially crystalline SiO2-ba sed surface layers were formed, via low-temperature oxidation (at 1200 degr eesC), on the faces to be joined. Joining of the surface-coated pieces coul d then be performed in an inert environment at typical sintering/joining te mperatures (i,e., 1700 degreesC), with or without applied gas pressure, via a transient viscous/liquid phase. This method was most effective for Si3N4 ceramics with single oxide sintering additives when a thin (similar to1 mu m thick), highly smooth (RMS roughness <60 nm) SiO2 layer was formed, and e ssentially 'pore-free' joints could be formed. However, the method was less suitable for a multi additive SiAlON material under current experimental c onditions, as relatively high roughness (RMS roughness >400 nm) oxide scale s formed, leaving residual porosity at the joint interface.