Microstructures and joining mechanism of vacuum brazing of SiO_2f/SiO₂ composite to Mo alloy using Ag-Cu-In-Ti brazing fillers mechanism

Three kinds of Ag-Cu-In-Ti brazing filler were designed for joining of SiO_2f/SiO₂ composite to Mo alloy. The brazing experiment was conducted at 800 ℃ for 10 min under vacuum condition. The joint shear strengths were tested at ambient temperature. The microstructures were observed under a scanning electron microscopy(SEM), and the reaction products were analyzed by EPMA, EDS and XRD. The results show that the joints brazed with 1^# brazing filler offer the maximum shear strength of 24.1 MPa. Part of Ti element is enriched at interfacial reaction layer, the other part is distributed within the joint matrix as Cu₃Ti to enhance the joint. The mechanism of joining SiO_2f/SiO₂ composite by Ag-Cu-In-Ti brazing filler is the reaction of Ti with SiO₂: Ti+SiO₂→TiSi₂+TiO, followed by the subsequent reaction: Ti+Cu+O→Cu₃Ti₃O. The product sequence for 1^# joint can be described as the following: SiO₂→Cu₃Ti₃O+TiO+TiSi₂→Ag(s,s)/Cu₃Ti/Cu(s,s)→Cu₃Ti+TiO→Mo.