Effect of Ni content on microstructure and properties of fibers-reinforced Ag-28Cu-Ni alloy

Ag-28Cu-xNi (x = 0, 0.75, 1, 2 wt%), alloys are silver-based vacuum filler metals. The effect of Ni additions on melting characteristics, phase structure, as-cast and cold-working microstructures, interface morphology, mechanical properties and brazing properties of Ag-28Cu-Ni alloys were investigated, respectively. The results indicated that the solidus temperature, liquidus temperature and temperature range of the solid-liquid phase respectively increase from 778.1, 780.2, 2.1 to 783.6 °C, 815.4 °C, 31.8 °C as the Ni content increase from 0 to 2 wt%. Ag-28Cu-Ni alloy are mainly composed of Ag-rich α-phase, Cu-rich β-phase and (Ag+Cu) eutectic structures. The addition of Ni in the Ag-28Cu alloy will transform the eutectic structure into the segregation structure. Besides, with the increase of deformation, the tensile strength of Ag-28Cu-Ni alloy increases with the appearance of deformation texture. With the Ni content increase from 0 to 2 wt%, the spreading rate of Ag-28Cu-Ni filler metal on the Cu substrate increase from 158 to 176 cm² g^-1 and the shear strength of the Cu/Ag-28Cu-Ni/Cu brazed joint increase from 161 to 183 Mpa. Furthermore, the tensile fracture initiation source of the Cu/Ag-28 Cu/Cu joint is located at the interface between the Cu-rich phase and the Ag-rich phase, and the crack propagates in the Ag-rich phase of the fracture joint. But the cracks crack and expand in the Ag-rich phase of the brazing seam as the Ni content increases.