Joining of Si3N4 ceramic using PdCo(NiSiB)-V system brazing filler alloy and interfacial reactions

The wettability of V-active PdCo-based alloys on Si3N4 ceramic was studied with the sessile drop method. And the alloy of Pd50.0-Co33.7-Ni4.0-Si2.0-B0.7-V9.6 (wt%), was developed for Si3N4 ceramic joining in the present investigation. The rapidly-solidified brazing foils were fabricated by the alloy Pd50.0-Co33.7-Ni4.0-Si2.0-B0.7-V9.6. The average room-temperature three-point bend strength of the Si3N4/Si3N4 joints brazed at 1453 K for 10 min was 205.6 MPa, and the newly developed braze gives joint strengths of 210.9 MPa, 206.6 MPa and 80.2 MPa at high temperatures of 973 K, 1073 K and 1173 K respectively. The interfacial reaction products in the Si3N4/Si3N4 joint brazed at 1453 K for 10 min were identified to be VN and Pd2Si by XRD analysis. Based on the XEDS analysis result, the residual brazing alloy existing at the central part of the joint was verified as Co-rich phases, in which the concentration of element Pd was high up to 18.0-19.1 at%. The mechanism of the interfacial reactions was discussed. Pd should be a good choice as useful alloying element in newer high-temperature braze candidates for the joining of Si-based ceramics.