Magnesiothermic reduction of SiO2f/SiO2 composites for brazing with Nb using AgCuTi

Brazing SiO2f/SiO2 composites is always associated with the problem of poor wettability, and directly brazing SiO2f/SiO2 to Nb with AgCuTi cannot obtain the high strength joints. To overcome the problem, strong binding Si layer was synthesized on SiO2f/SiO2 surface by magnesiothermic reduction method. Results show that the content of Si raised to twice higher than original composites. The contact angle of AgCuTi on SiO2f/SiO2 composites was decreased from 95.9 degrees to 34.7 degrees via reducing SiO2 into Si. Due to the reaction of Si and Mg, SiO2 matrix were corroded to some extent inducing the zigzag reaction layer in the joints. With the increasing of Si content, O contained compounds in reaction layer were replaced by Ti-Si phase. And low thermal expansion Ti5Si3 particles would disperse near the reaction layer to maintain the stability of reaction layer. The highest shear strength reached 38.3 MPa with 4 h reducing treatment.