MICROSTRUCTURAL EVOLUTION AND MECHANICAL-PROPERTIES OF BRAZE JOINTS IN TI-13.4AL-21.2NB

Braze joints in Ti-13.4Al-21.2Nb were made using several filler metal compositions based upon the Ti-Cu-Ni ternary system. Specimens were va cuum brazed, using filler metal pre-placed between bonding surfaces. T wo types of braze foil, one produced by rapid solidification technique s and one formed by a roll bonding process, were examined. Mechanical test results indicated that substantial differences in braze joint str ength could be obtained From specimens prepared using foil manufacture d by the two different processes. Specifically, for the higher alloyed composition, a laminated foil produced joints with lower room tempera ture tensile strength compared to its rapidly solidified counterpart. Specimens prepared using laminated foil typically failed through the b raze joint and had low strength. This behavior was related to the pres ence of an increased amount of centerline alpha-two phase in the braze joints made using the laminated filler metals. The formation of this microstructural feature was influenced by segregation of the filler me tal alloying elements, nickel and copper. Braze joints prepared using laminated foils exhibited higher levels oi segregation, even after lon g hold times at the brazing temperature, than joints made using rapidl y solidified foil.