Study on the Effect of “3D-rGO” Buffer Layer on the Microstructure and Properties of SiO_2f/SiO₂ and TC4 Brazed Joint

Brazing a SiO_2f/SiO₂ composite with metals is often faced with two problems: poor wettability with the brazing alloy and high residual stress in the joint. To overcome these problems, we report a combined method of selective etching and depositing reduced graphene oxide (rGO) on the surface of a SiO_2f/SiO₂ composite (3D-rGO-SiO_2f/SiO₂) to assist brazing with TC4. After the combined treatment, a “3D-rGO” buffer layer formed on the surface layer of the SiO_2f/SiO₂, and the contact angle was reduced from 130° to 38°, which meant the wettability of active brazing alloy on the surface of SiO_2f/SiO₂ was obviously improved. In addition, the “3D-rGO” buffer layer contributed to fully integrating the brazing alloy and SiO_2f/SiO₂; then, the infiltration of the brazing alloy into the surface layer of the SiO_2f/SiO₂ was enhanced and formed the reduced graphene oxide with a pinning structure in the three dimensional (“3D-pinning-rGO”) structure. Moreover, the joining area of the brazing alloy and SiO_2f/SiO₂ was expanded and the mismatch degree between the SiO_2f/SiO₂ and TC4 was reduced, which was achieved by the “3D-pinning-rGO” structure. Furthermore, the concentration of the residual stress in the SiO_2f/SiO₂-TC4 joints transferred from the SiO_2f/SiO₂ to the braided quartz fibers, and the residual stress reduced from 142 MPa to 85 MPa. Furthermore, the 3D-pinning-rGO layer facilitated the transfer of heat between the substrates during the brazing process. Finally, the shear strength of the SiO_2f/SiO₂-TC4 joints increased from 12.5 MPa to 43.7 MPa by the selective etching and depositing rGO method.