| Summary: | The study was designed to investigate the synergic effect of Ti and Sn in the active metal brazing of Al<sub>2</sub>O<sub>3</sub> ceramic to copper brazed, using the multicomponent Ag-Cu-Zr filler alloy. Numerous fine and hexagonal-shaped rod-like ternary intermetallic (Zr, Ti)<sub>5</sub>Sn<sub>3</sub> phase (L/D = 5.1 ± 0.8, measured in microns) were found dispersed in the Ag-Cu matrix of Ag-18Cu-6Sn-3Zr-1Ti alloy, along with the ternary CuZrSn intermetallic phases. An approximate 15° reduction in contact angle and 3.1 °C reduction in melting point are observed upon the incorporation of Ti and Sn in Ag-18Cu-3Zr filler. Interestingly, the interface microstructure of Al<sub>2</sub>O<sub>3</sub>/Cu joints brazed by using Ag-18Cu-6Sn-3Zr-1Ti filler shows a double reaction layer: a discontinuous Ti-rich layer consisting of (Cu, Al)<sub>3</sub>(Ti, Zr)<sub>3</sub>O, TiO, and in-situ Cu-(Ti, Zr) precipitates on the Al<sub>2</sub>O<sub>3</sub> side and continuous Zr-rich layer consisting of ZrO<sub>2</sub> on the filler side. The shear strength achieved in Al<sub>2</sub>O<sub>3</sub>/Cu joints brazed with Ag-18Cu-6Sn-3Zr-1Ti filler is 31% higher, compared to the joints brazed with Ag-18Cu-6Sn-3Zr filler. Failure analysis reveals a composite fracture mode indicating a strong interface bonding in Al<sub>2</sub>O<sub>3</sub>/Ag-18Cu-6Sn-3Zr-1Ti filler/Cu joints. The findings will be helpful towards the development of high entropy brazing fillers in the future.
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