Microstructure evolution and bonding strength of the Al2O3/Al2O3 interface brazed via Ni-Ti intermetallic phases

In this study, Al2O3 workpieces were vacuum brazed by using Ni-45Ti binary alloy. The interfacial microstructure evolution of the joints obtained at different brazing temperatures was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The bonding strength of the joints was measured by shear testing. The results indicated that Ni2Ti4O and AlNi2Ti were the main reaction products in the joint areas. Moreover, the Ti2Ni intermetallic compound formed in the brazing seam. The typical layer structure of the brazed joints was Al2O3/AlNi2Ti/Ni2Ti4O/Ti2Ni + NiTi/Ni2Ti4O/AlNi2Ti/Al2O3. With the brazing temperature increasing, the thickness of the Ni2Ti4O reaction layer adjacent to the Al2O3 substrate increased significantly, while the AlNi2Ti phase had a tendency to dissolve with the brazing temperature increasing. The mechanism for the microstructure evolution was also discussed. The maximum shear strength of 125.63 +/- 4.87 MPa of the joints was obtained when brazed at 1350 degrees C for 30min. The fracture occurred hardly in the interface between Al2O3 and Ni-45Ti filler alloy.