Joining of Silicon Nitride Using Amorphous Cu-Ti Filler Metal(Materials, Metallurgy & Weldability)

Si3N4/Si3N4 joint was made using Cu66Ti34, Cu50Ti50 and Cu43Ti57 amorphous filler metals, where pressureless sintered Si3N4 was used. The joining strength of Si3N4 joint was measured by fracture shear testing, and the joining mechanism was investigated by microstructure observation with SEM, and elements analyses at the joint interface with EDX and EPMA. The results obtained are summarized as follows.(1) The molten Cu-Ti alloys containing 20 at% Ti or more exhibit the equilibrium contact angle of about 8°, and are applicable to the filler metal for joining of Si3N4.(2) The joining strength of Si3N4 using Cu66Ti34 filler is higher than that of Si3N4 using other Cu-Ti fillers at any brazing temperature except for brazing temperature of 1273 K. Thus, the joining strength of Si3N4 with Cu66Ti34 filler shows the maximum value of 313.8 MPa at brazing temperature of 1323 K. At the brazing temperature of 1373 K, Si3N4 joint with Cu50Ti50 filler shows the maximum value of 176.5 MPa at brazing time of 1.8 ks, and gradually decreases with longer brazing lime, and to 19.6 MPa at brazing time of 7.2 ks. The elevated temperature fracture shear strength of Si3N4 joint brazed at 1373 K for 1.8 ks using Cu50Ti50 filler increases to 199.1 MPa at 373 K, and gradually decreases to 105.9 MPa at 973 K.(3) During brazing Ti in molten Cu50Ti50 filler reacts with Si3N4 by the following reactions. Si3N4(s) +4Ti(1)=4TiN(s)+3Si(s), and Si3N4(s)+9Ti(1)=4TiN(s)Ti5Si3(s). TiN at the interface between Si3N4 and the filler, Ti5Si3, and Cu-Si phase at the central part of the filler are formed. The activation energy for growth of TiN at the joining interface is 206.3 kJ/mol, and the growth of TiN is dominated by the diffusion of N in TiN. The silicon content of the Cu-Ti phase increases about 7 at%Si to about 20 at%Si with increasing the brazing temperature.