Interfacial structure and fracture behavior of TiB whisker-reinforced C/SiC composite and TiAl joints brazed with Ti-Ni-B brazing alloy

In situ formed TiB whisker-reinforced TiAl and C/SiC joints, containing 30% of TiB whiskers by volume, were produced by vacuum brazing with (Ti-66Ni)_1-xB_x (x=3wt.%) alloy at 1160°C for 10min. The brazing alloy prepared by arc-melting was mainly comprised of TiNi₃ and TiNi eutectic microstructure, in which some black TiB₂ blocks formed. TiB₂ was transformed into TiB whiskers during brazing due to the successive dissolution of TiAl substrate. The interfacial structure of the brazed joint consisted of β reaction layer transformed from TiAl, TiB whisker-reinforced central zone and TiC reaction layer adjacent to C/SiC. The in situ formed TiB whiskers were beneficial in reducing the joint residual stresses and reinforcing the joint. The average shear strength reached 90MPa and 65MPa at room temperature and 600°C, respectively. Fracture primarily propagated in the SiC matrix with the carbon fiber being pulled out. Contributing factors to the high strength included the possibility of the pull-out of carbon fibers, the diversion of crack propagation direction and the " nail effect" which formed by the infiltration of the brazing alloy.