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. (paper)