Effect of in situ synthesized TiB whisker on microstructure and mechanical properties of carbon–carbon composite and TiBw/Ti–6Al–4V composite joint

Carbon–carbon composite (C–C composite) and TiB whiskers reinforced Ti–6Al–4V composite (TiBw/Ti–6Al–4V composite) were brazed by Cu–Ni + TiB2 composite filler. TiB2 powders have reacted with Ti which diffused from TiBw/Ti–6Al–4V composite, leading to formation of TiB whiskers in the brazing layer. The effects of TiB2 addition, brazing temperature, and holding time on microstructure and shear strength of the brazed joints were investigated. The results indicate that in situ synthesized TiB whiskers uniformly distributed in the joints, which not only provided reinforcing effects, but also lowered residual thermal stress of the joints. As for each brazing temperature or holding time, the joint shear strength brazed with Cu–Ni alloy was lower than that of the joints brazed with Cu–Ni + TiB2 alloy powder. The maximum shear strengths of the joints brazed with Cu–Ni + TiB2 alloy powder was 18.5 MPa with the brazing temperature of 1223 K for 10 min, which was 56% higher than that of the joints brazed with Cu–Ni alloy powder.

► In situ TiB whiskers spread fairly randomly throughout the brazing alloy of the joint.
► In situ TiB whiskers inhibit the growth of the compound.
► TiB acts as heterogeneous nucleation sites for the formation of grain boundary Ti–Cu compounds.
► The joint shear strength with pure Cu–Ni is lower than that of uniformly distributed TiB whiskers.
► TiB plays the roles of reinforcement, refinement, and alleviation of thermal residual stress.