BRAZED JOINT PROPERTIES AND MICROSTRUCTURE OF SCS-6/BETA-21S TITANIUM MATRIX COMPOSITES

The properties and microstructure of brazed joints of SCS-6 SiC fiber reinforced beta 21S (Ti-15Mo-2.7Nb-3Al-0.2Si, wt-%) titanium matrix composite (TMC) were investigated. Brazed joint specimens were fabricated from TMC using two different forms of commercially available Ti-15Cu-15Ni braze filler metal. The brazed joint specimens were tested in air at room temperature and 1500 degrees F (815 degrees C) using overlap tensile shear (OLTS) tests. Metallurgical and fractographic analyses were used to characterize the microstructure, brazing filler metal/TMC interactions, and joint failure modes. The fractographic results indicated that TMC delamination is a dominant failure mode for this type of joint. At room temperature, the TMC brazed joint specimens failed by TMC delamination and TMC tensile failure, with the brazed joint remaining intact. Therefore, the performance of the brazed joint specimens at room temperature is limited by the interlaminar strength of the TMC and not by the braze strength. At 1500 degrees F, the TMC brazed joint specimens exhibited a combination of delamination and braze shear failure. Thus, the high-temperature performance of the brazed joint specimens may be limited by both the TMC interlaminar properties and the strength of the braze.