Wetting and joining of porous Si3N4 and dense Si3N4 ceramics with in-situ formed β-spodumene/spinel glass-ceramic interlayer

Efficient joining materials and techniques are of critical significance for the integration of ceramics in high performance structures. Porous Si3N4 has been successfully joined to dense Si3N4 by using a novel glass-ceramic based on the Li2O-MgO-Al2O3-SiO2 system. In terms of elucidating the microstructure of joints, systematic approaches were made, including scanning electron microscopy, transmission electron microscopy and X-ray diffraction, to characterize the glass/ceramic interface and to determine the influence of joining temperature on the microstructural evolution. In addition, the extent to which temperature the joint could withstand has been determined. It is suggested that the glass shows good wettability and thermomechanical compatibility with both porous and dense Si3N4 substrates. The micron-size beta-spodumene, along with the submicronic spinel are identified as the main crystallization of the glass-ceramic interlayer forming an intergranular network structure. The infiltration layer, consisting of glass and rod-like Si3N4 grains, shows increased elastic modulus and microhardness, which helps improve the stress tolerance of the joint. Accordingly, this joint exhibits an extraordinary high room-temperature shear strength (112 +/- 10 MPa) and a high-temperature resistance.