Microstructures and joining characteristics of NbSS/Nb5Si3 composite joints by newly-developed Ti66-Ni22-Nb12 filler alloy

Abstract New filler alloy composition of Ti66-Ni22-Nb12 (at.%) was designed for NbSS/Nb5Si3 composite joining and the brazing experiment was conducted at 1200 °C and 1260 °C, respectively. Compared with the previously reported Ti-Ni-Nb system filler alloys, the concentration of Ni was significantly decreased from 40 at.% to 22 at.%. The filler alloy was fabricated into brazing foils by rapid solidification technique, with about 60 μm thickness. The brazing seam mainly consisted of Nb solid solution, (Nb,Ti)5Si3 and residual NiTi2 phases. Due to the high content of stabilization element Ti in the filler alloy, hexagonal γ-Nb5Si3 phase was detected in the brazing seam. When increasing brazing temperature or prolonging brazing time, the amount of residual NiTi2 phase within the joint was gradually decreased. The joints brazed at 1260 °C for 60 min exhibited three-point bend strength of 317 MPa