Wettability of PdNi(Co)-Cr alloys on Si3N4 ceramic and joining of Si3N4 to Si3N4

Eight kinds of PdNi(Co)-Cr alloys were designed, and their wettability on Si3N4 ceramic was studied with the sessile drop method. Under the vacuum heating condition of 1,523 K/30 min, Pd60-Ni40 alloy showed a contact angle of 28 degrees on Si3N4 ceramic, and the reaction band between it and the Si3N4 consisted of the mixture of (Pd, Ni) solid solution and (Pd, Ni)-silicides. It was found that Cr addition into the Pd-Ni alloys further improved their wettability. Pd60-Co40 alloy gave a contact angle of 134 degrees. When 8 wt.% Cr was added into Pd-Co alloy, its contact angle was remarkably decreased to 44 degrees. The reaction products at the interfaces were examined by SEM equipped with an X-ray energy-dispersive spectrometer, and the corresponding interfacial reaction mechanism was also discussed. The formation of Pd2Si is evident at the interfaces. PdCo(Ni,Si,B)-(20 similar to 25)Cr alloy was designed as a filler metal and was produced into filler foils by a rapidly-solidifying technique, and they were used for the brazing of Si3N4/Si3N4. The Si3N4/Si3N4 joints brazed at 1,523 K for 10 min exhibited an average three-point bend strength of 107.7 MPa at room temperature.