Joining of silicon nitride to metals by vacuum brazing

Vacuum brazing was used to prep. silicon nitride-metal joints for service temps. exceeding 1000 DegC. The active brazing filler metals commonly used in ceramic-metal joining are not suitable for these temps. because of their low melting ranges. The joining method used was to coat the ceramic surface with an active element (titanium) and to use an inactive palladium-nickel alloy as the filler metal. Tungsten and molybdenum interlayers were used to reduce the thermal residual stresses of the joint area. Some ref. joints were made using active filler metals. The brazed samples were tested nondestructively after joining using the high-frequency ultrasonic examn. method (C-SAM). The mech. properties of the joints were verified with a shear-strength test and the fracture surfaces were inspected visually. A clear correspondence could be detected between the C-SAM images, joint strengths and fracture surfaces. The most significant problems arose from the porosity of the joints due to the high brazing temps. as well as from the cracking of the ceramic due to the high residual stresses. [on SciFinder (R)