Enhanced bonding of Al2O3/Al2O3 joints brazed by Ni50Ti50 master alloy interlayer

Al2O3 ceramics were successfully brazed under high vacuum conditions using the active Ni50Ti50 master alloy at 1320 °C with different holding time. The interfacial microstructure of the joint was characterized using SEM, EDS and TEM. The effects of holding time on the microstructure evolution and mechanical properties of the joints were investigated. The results revealed that the typical structure of the Al2O3/Ni–Ti joint brazed at 1320 °C for 45 min was Al2O3/AlNi2Ti + Ni2Ti4O/Ni2Ti4O/TiNi. Ni2Ti4O was continuously distributed as a layer adjacent to the Al2O3 substrate, whereas columnar AlNi2Ti phase existed in the Ni2Ti4O layer near the Al2O3 side. With the prolongation of holding time, the thickness of Ni2Ti4O layer increased obviously, and AlNi2Ti became longer and coarser. The maximum shear strength of 109 MPa was obtained when the joint was brazed at 1320 °C for 45 min. The hardness, Young's modulus and elastic recovery of the phases across the joints became a gradient property. The interfacial reaction layer with appropriate thickness was found beneficial for enhancing the Al2O3/Ni–Ti/Al2O3 joint strength.