Influence of Silicon Nitride Properties on Bonding Strength of Silicon Nitride and Stainless Steel Brazed Joints

To develop a new airtight seal parts for BWR in-core detector, brazing of silicon nitride and a metal(SUS304) was examined. In this paper, to clarify the relation between material properties of silicon nitride and bonding strength of the seal parts, tensile test of the seal parts specimen using various kind of silicon nitride was carried out. Cone shaped silicon nitride was applied at a center of the specimen and a copper interlayer which edge was tapered to 40° was inserted between silicon nitride and a metal(SUS304). Copper-titanium brazing alloy was used for brazing. The relation between mechanical properties of the silicon nitride and tensile strength of the joints indicated that the silicon nitride fracture toughness is more important than silicon nitride bending strength for determining over all joint strength. It is clarified that to obtain high tensile strength of the silicon nitride and stainless steel joints, that is to obtain highly reliable seal parts, it is necessary to use high fracture toughness silicon nitride in addition to an appropriate interlayer shape.