Brazing of SiO2f/SiO2 composite modified with few-layer graphene and Invar using AgCuTi alloy

Abstract

Abstract Due to the poor wettability of the AgCuTi alloy on the SiO 2f /SiO 2 composite, direct brazing of the composite with an Invar alloy could hardly achieve a reliable joint. To overcome that, the SiO 2f /SiO 2 composite was decorated with few-layer graphene (FLG) by a plasma enhanced chemical vapor deposition (PECVD) method. Sessile drop experiments indicate that the contact angle dropped from 123.8° to 50.7° after FLG was grown on the surface of the SiO 2f /SiO 2 composite. Afterwards, the effects of brazing temperature and Ti contents on the microstructure evolution and mechanical properties of joints (Invar/SiO 2f –SiO 2 modified with FLG) were investigated. The typical interface structure of the joint is SiO 2f –SiO 2 /Ti 5 Si 3 + TiO 2 + Cu x Ti 6 − x O(x = 2,3)/Ag(s,s) + Cu(s,s) + Cu–Ti blocks/wave-like Fe 2 Ti + Ni 3 Ti/Ag(s,s) + Cu(s,s) + Fe 2 Ti + Ni 3 Ti blocks/Invar. As the brazing temperature and Ti contents increase, the reaction layer on the SiO 2f /SiO 2 side becomes thicker and cracks gradually propagate. Meanwhile, a few dispersive Fe 2 Ti + Ni 3 Ti phases change into large-area wave-like compounds and more Cu–Ti compounds form with the increase of the Ti content. The microstructure evolution significantly affects the shear strength of the brazed joints. The highest shear strength is 26 MPa brazed at 860 °C for 10 min with 4.5 wt.% Ti content.