Microstructure and Mechanical Properties of Vacuum Brazed Nb_SS/Nb₅Si₃ Composite Joints Using Ni-Based Filler Alloys

Vacuum brazing of Nb_SS/Nb₅Si₃ composite was performed with BNi2 and BNi5 filler alloys at 1293-1423 K for 1800 seconds. The joint microstructures were examined by a scanning electron microstructure (SEM) equipped with an X-ray energy-dispersive spectrometer (XEDS), and shear test for the brazed joints was conducted at room temperature. The Nb_SS/Nb₅Si₃ joint brazed with BNi2 filler alloy at 1293 K mainly consisted of Ni₃Si + Nb₃Si, Ni_SS and borides. As the brazing temperature increased to 1423 K, Cr₂Nb and NbNi phases were formed and the shear strength of the joints was increased from 180 to 253 MPa. Concerning the joints brazed with BNi5 filler at 1423 K, they exhibited an average strength of 274 MPa, and the joint micro-hardness was lower than BNi2 filler. The BNi5 filler alloy not only raised the shear strength but also decreased the joint brittleness to some extent. As a new finding in this study, 4-5 at. pct Ni had been dissolved into (Nb,Ti)_SS in the Nb_SS/Nb₅Si₃ composite, providing a new insight into the design of novel specific filler material for Nb_SS/Nb₅Si₃ joining.