Joining of pressureless-sintered SiC to stainless steel using Ag-Cu alloy and insert-metals

Brazing of pressureless-sintered SiC to stainless steel using Ag-28 wt% Cu alloy was studied. In SiC plate joined to stainless steel rod (6 mm in diameter) using an Ag-Cu alloy powder containing 1.5 wt% Ti, the bond strength increased with decreasing brazing temperature and holding time. When the increased size of stainless steel plate (10 x 10 x 4 mm), joining was unsuccessful by the method mentioned above and even with Ti insert-metal. However, simultaneous use of Ti and Mo as insert-metal gave a good bonding in the order SiC/Ti/Mo/stainless steel, because of relaxation of residual stress due to thermal expansion mismatch. The shear strength was 30 - 50 MPa. A thin layer, probably Ti3SiC2, was observed at the interface between SiC and brazing filler immediately after melting. But with increasing both temperature and time, Ti5Si3(C) and TiCx were formed if Ti was continuously provided from the brazing filler. Since the interface of Ti3SiC2 and either Ti5Si3(C) or TiCx seemed to be brittle, the formation of Ti5Si3(C) and TiCx decreased the bond strength. At lower temperature and short time, a high bond strength is expected when Ti was inserted in contact with SiC. (author)