Active metal brazing of silicon nitride ceramics using a Cu-based alloy and refractory metal interlayers

Silicon nitride/silicon nitride joints with refractory metal (W and Mo) interlayers were vacuum brazed using an active braze, Cu-ABA (Cu–3Si–2Al–2.25Ti, wt%), and two interlayer arrangements in a double-lap offset configuration: Si3N4/Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si3N4 and Si3N4/Cu-ABA /Si3N4. Titanium segregated at the Si3N4/Cu-ABA and Mo/Cu-ABA interfaces, but not at the W/Cu-ABA interface. The room-temperature compression-shear strength values of Si3N4/Cu-ABA/Si3N4 and Si3N4/Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si3N4 joints were 118±24 MPa and 22±5 MPa, respectively. Elevated-temperature compression tests showed that Si3N4/Cu-ABA/Si3N4 joints had strength of 31±6 MPa at 1023 K and 17±3 MPa at 1073 K. Likewise, Si3N4/Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si3N4 joints had strength of 19±4 MPa at 1023 K and 13±3 MPa at 1073 K. Knoop microhardness profiles revealed hardness gradients across the joints. The effect of joint microstructure and test configuration on the mechanical behavior is discussed.