The Technology Of Joinning Silicon Nitride Ceramics

The joining technology of large-scale or complex components as Si₃N₄/SiC ceramic crucible and Si₃N₄ ceramic riser tube used in the melting and foundry industry of aluminium alloy was studied in this paper, which objectives is to reduce the difficulty and cost of fabrication and improve the reliability. A kind of pressless joining technology was studied aimed at Si₃N₄/SiC ceramic, a joining process and two adhesive systems were designed. A kind of pressless reaction sintered joining technology was studied aimed at Si₃N₄ ceramic, a joining process and four adhesive systems were designed. The joining properties and joining mechanism were discussed. Then the adhesive and technical were optimized. Furthermore, the reactions between adhesives and Al alloy were studied. The main conclusions drawn are as follows:(1) The slurry properties of the Bauxite—Borax adhesive is poor in plasticity and conglutination with Si₃N₄/SiC ceramics, which also solidify easily. There are a lot of defects in the joint. The optimal adhesive component is bauxite 70%, borax 30%, and the optimal technical, parameter is 900℃,3h. The tensile strength achieved 1.2MPa and would not decrease after thermal shock. The liquid produced by adhesive could wet and diffuse into the parent material to form interface bond and intergrate them.(2) The slurry properties of the SiC—Aluminium phosphate adhesive is excellent in fluidity and conglutination with Si₃N₄/SiC ceramics, which also has a high content of solid phase. The adhesive appears 0.1% expansion during the process, which is useful for joining properties. The optimal technical parameter is 900℃,3h. The tensile strength achieved 1.8MPa and remained 78% after themal shock. The joint is densified by micronized SiO₂ and Al(H₂PO₄)₃ throught sintering and joining, forming interface bond to intergrate the adhesive and the parent material.(3) The slurry properties of the Magnesia—Bauxite adhesive is poor in plasticity and conglutination with Si₃N₄ ceramics, which also solidify easily. There are a lot of defects in the joint, as a result, the tensile strength is only 0.9 MPa. The liquid produced by adhesive could wet and diffuse into the parent material to form interface bond , which intergrate the two parts. The slurry properties of Si adhesive has a poor properties and give 1.5MPa tensile strength. The Si—Magnesia—Bauxite adhesive can not form good joint.