EFFECT OF METALLURGICAL BEHAVIOR AT THE INTERFACE BETWEEN CERAMIC ANDINTERLAYER ON THE SI3N4 1.25CR-0.5MO STEEL JOINT STRENGTH/

By using newly developed CuNi5 similar to 25Ti16 similar to 28B rapidl y solidified brazing filler the joining of Si3N4/1.25Cr-0.5Mo steel ha s been carried out with interlayer method. If employing the interlayer structure of steel (0.2 mm)/W (2.0 mm)/Ni(0.2 mm), the joint strength can be increased greatly compared with employing that of Ni/W/Ni, and the three point bend strength of the joint shows the value of 261 MPa . The metallurgical behaviour at the interface between Si3N4 and the i nterlayer has been studied. It is found that Fe participated in the in terfacial reactions between Si3N4 and the brazing filler at the Si3N4/ steel (0.2 mm) interface and the compound Fe5Si3 was produced. However , since the reactions of Fe with the active Ti are weaker than those o f Ni with Ti, the normal interfacial reactions were still assured at t he interface of Si3N4/steel (0.2 mm) instead of Si3N4/Ni (0.2 mm), res ulting in the improvement of the joint strength. The mechanism of the formation of Fe5Si3 is also discussed. Finally, some ideas to further ameliorate and simplify the interlayer structure are put forward.