Heat-Resistant Active Brazing of Silicon Nitride Part 2: Metallurgical Characterization of the Braze Joint

摘要

Metallurgical characteristics of silicon nitride braze joints fabricated for service at elevated temperatures are discussed in Part 2. Filler metals containing palladium, platinum, copper, nickel, and silver were investigated. Most filler metals were arc melted, and then differential thermal analysis was performed to determine the liquidus and solidus temperatures. Wetting tests were employed as selection criteria. The silicon nitride substrate was premetallized at a lower temperature with an AgCulnTi filler metal prior to brazing at elevated temperatures. The reaction layer developed during premetal-lizing remained stable at the higher brazing temperature, controlling the silicon nitride decomposition. Other braze joints were fabricated without premetal-lizing, using a Co-10Ti melt-spun foil, in order to avoid an extra processing step. Thermogravimetric results showed that the Co-10Ti filler metal oxidized quickly at first but passivated almost as fast. Over-all it had good oxidation resistance.