Improvement of Si<SUB>3</SUB>N<SUB>4</SUB>/Steel Brazing Strength Utilizing the Martensitic Transformation

This work provides a novel process in which the highly hard steel and Si3N4 are strongly joined to each other. Heat-resistant steel, Kovar, NiCrMo steel and carbon steel were used as the metallic materials. Ni/W-alloys were inserted between Si3N4 and metallic materials as buffer layers.The multi buffer layer of combined Ni/W-alloy/Ni which reduces the residual stress, gives over 400 MPa in joining strength for the combination of Si3N4/Heat-resistant steel. For Si3N4/Kovar, Si3N4/NiCrMo steel and Si3N4/carbon steel show the joining strengths of 370, 612 and 317 MPa, respectively. In the thermal shrinkage curves from brazing temperature to room temperature of the metallic materials, the heat-resistant steel and NiCrMo steel show a volume expansion due to the martensitic transformation which increases the joining strength.