Vacuum brazing of C/C composite to TC4 alloy using nano-Al2O3 strengthened AgCuTi composite filler

•C/C composite was successfully brazed using nano-Al2O3 strengthened AgCuTi filler.•The addition of nano-Al2O3 improves the performance of joints.•The highest shear strength of joints reached 27.8 MPa.•The fracture positions are related to temperatures and orientations of carbon fiber.

Vacuum brazing of C/C composite to TC4 alloy was performed using nano-Al2O3 strengthened AgCuTi composite filler. The microstructure and main properties of the composite filler were characterized. The typical interfacial microstructure of brazed joint is TC4/diffusion layer/Ti–Cu intermetallic layers/Ag(s,s) + Cu(s,s) + TiCu/TiC/C/C composite. The effects of brazing temperature and addition of nano-Al2O3 on microstructure of brazed joints were investigated by SEM, EDS, TEM and XRD. The diffusion layer, Ti–Cu intermetallic layers and TiC layer thicken with the increasing temperature while the thickness of brazing seam decreases. The TiCu phase in brazing seam excessively develops and almost replaces the Ag(s,s) and Cu(s,s) when brazing temperature reaches 920 °C. The addition of nano-Al2O3 improves the performance of brazed joints by inhibiting the growth of Ti–Cu layers adjacent to TC4 side and offering dispersive nucleation sites for TiCu phase in brazing seam. The joint brazed at 880 °C for 10 min exhibits the highest shear strength of 27.8 MPa. The fracture positions of brazed joints are also discussed in this paper.

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