MECHANICAL PROPERTIES OF SILICON NITRIDE/STEEL JOINT WITH NI-INTERLAYER

摘要

In order to improve the room-temperature fracture strength of the brazed silicon nitride (Si_3N_4)/steel joint, the use of creep-resistant and oxidation-resistant Ni-interlayer has been attempted. The present study deals with two different methods (i.e. direct brazing method, and double active metal brazing method) for joining ceramic and metal materials. The dissolution of Ni into the brazing alloy for the joint that was fabricated by direct brazing method resulted in the decrease of the fracture strength with the increase in the thickness of Ni-interlayer. The cause of the strength reduction was attributed to be (1) by the formation of Ni-Ti compound inhibiting the effective reduction of the residual stress, and/or (2) by the depletion of Ti near the interface restricting an adequate interface bonding. The double active metal brazing method enabled an effective reduction in the dissolution of Ni-interlayer into the brazing alloy, which lead to the increase of the joint fracture strength. The finite element analysis was performed to calculate the residual stress within the joint.