V-containing-active high-temperature brazes for ceramic joining

Abstract

V-containing-active high-temperature brazing alloys were designed for ceramic joining, including PdCo–V, AuPdCoNi–V, AuCuPd–V, and CuPd–V system alloys. The joined ceramics or ceramic composites include Si3N4 ceramic, AlN ceramic, carbon fiber-reinforced silicon carbide composite (Cf/SiC), and C/C composite. The dynamic wettability of the V-containing brazes on ceramic or composite was studied with the sessile drop method. Based on the wetting experiment results, several alloys were chosen as the brazing filler metal. It was verified that during the brazing process, the reactions between the filler metal and the Si3N4 or AlN ceramic caused the formation of V–N layer at the interface close to the ceramic surface. The V–C compound was detected at the reaction interface between the V-containing-active filler metal and C/C composite or Cf/SiC composite. The formation of V–N or V–C layer played an important role in the joining of the ceramic or the ceramic composite. Both of the Si3N4–Si3N4 and Cf/SiC–Cf/SiC joints brazed with V-containing-active braze exhibited stable high-temperature property, and this should be attributed to the presence of refractory Pd2Si compounds within the joints. The newly developed V-containing-active brazes should have a potential to meet service temperatures of 973~1073 K, about 300 K higher than the AgCu–Ti brazing filler metals.