Interfacial microstructure and mechanical properties of TiAl and C/SiC joint brazed with TiH_2-Ni-B brazing powder

摘要

(TiH_2-66Ni)_(1-x)B_X (x = 3 wt.%) brazing powder was fabricated by mechanical milling of a TiH_2, Ni and B mixture with the milling time ranged from 30 to 180 min. TiAl alloy and C/SiC composite were successfully brazed using this filler metal at 1180 °C for 10 min. The microstructure and mechanical properties of the brazed joints were investigated. The typical microstructure of the joint was divided into three characteristic zones, including the TiC reaction layer formed adjacent to C/SiC composite, the TiB-whisker reinforced central zone, and the β layer transformed from TiAl alloy. The in situ synthesized TiB whiskers acted as an effective reinforcement phase aid to decrease the residual stress and improve the shear strength of the joints. The joint strength reached 10S MPa at room temperature, and cracks primarily propagated in the C/SiC substrate with the pull-out of carbon fibers and partially in the Tic layer and τ_3 phase. The joint strength decreased slightly with the testing temperature increased to 500 °C, and remained at 70 MPa when tested at 600 °C. The crack propagation path diverted from the TiC reaction layer to the τ_3 phase when the joint was tested at 600 °C.