Joining of Silicon Nitride by Local Heating for Fabrication of Long Ceramic Pipes

This study demonstrated that a long silicon nitride pipe of several meters with adequately strong joints can be fabricated by a local‐heating joining technique. Commercially available silicon nitride ceramic pipes sintered with Y₂O₃ and Al₂O₃ additives were used for parent material, and powder slurry of Si₃N₄‐Y₂O₃‐Al₂O₃‐SiO₂ system was brush‐coated on the rough or uneven end faces of the pipes. Joining was carried out by locally heating the joint region at different temperatures from 1500°C to 1650°C for 1 h with a mechanical pressure of 5 MPa in N₂ flow; using a horizontal electrical furnace specially designed for this experiment. The silicon nitride pipe 3‐m long was successfully fabricated without voids or cracks in the joint region, and the microstructure of the joint region was similar to that of the parent one. The joint strength was examined in flexure using specimens cut from the joined pipes, and those joined at 1600°C and 1650°C indicated the highest strength of about 680 MPa, which was almost the same as that of the parent material. This study also indicated that the slurry brush‐coating technique is advantageous to easily joining ceramic pipes with rough or uneven end faces, which is essentially important for practical use.