Interfacial microstructure and improved wetting mechanism of SiO_2f/SiO₂ brazed with Nb by plasma treatment

Due to the poor wettability with AgCuTi and high residual stress, it is difficult to achieve high-strength brazed joint of SiO_2f/SiO₂ (quartz fiber reinforced silica) with metals. Herein, plasma treatment as an effective approach was conducted to modify the surface state of SiO_2f/SiO₂ for better wettability and high-strength brazed joints. Based on SEM, Raman, XPS and wetting experiment analysis, the mechanism of plasma treatment on the improved wettability of SiO_2f/SiO₂ with AgCuTi is proposed. Plasma treatment can coat thin carbon film and form C-Si bonding on the surface of SiO_2f/SiO₂, which both show good wettability with AgCuTi. Therefore, the contact angle was notably reduced from 131° to 45° with only 5min plasma treatment on the SiO_2f/SiO₂. Afterwards, the effect of plasma treating time on the interfacial microstructure and mechanical property of SiO_2f/SiO₂-Nb joints were investigated in detail. It was found that adjusting the plasma treating time can control the distance of brazing alloy infiltration. Further, the shear strength and the fracture morphologies were closely related with the distance of brazing alloy infiltration. The infiltration of AgCuTi at the SiO_2f/SiO₂ side can significantly increase the bonding areas and reduce residual stress, and thus enhance the mechanical properties of brazed joints.