Tailoring κ phase via adding Cr to achieve strengthening-toughening of Cu-7Ni-7Al-4Fe-2Mn alloy

• Tailoring κ phase in nickel aluminum bronze via adding Cr. • Cr changes the lattice type of κ Ⅳ phase. • Cr changes the interface relationship between κ Ⅳ phase and matrix. • When the Cr content is high, the κ Ⅲ phase has a core–shell structure. • The addition of Cr improves the mechanical properties of the alloy. An investigation into the impact of varying Cr levels on the κ phase, grain dimensions, and mechanical properties of the Cu-7Ni-7Al-4Fe-2Mn alloy was carried out using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and an electronic tensile tester. It was discussed how Cr exists in the κ phase and the mechanism of the strengthening properties. As the Cr content increases, Cr progressively substitutes for Al in the Fe 3 Al phase. Concurrently, the Fe 3 Cr phase tends to change from the D0 3 structure to the L1 2 structure. In addition, as the Cr content increases, the size of the κ Ⅳ phase and the κ Ⅲ phase in the alloy also changes to a certain extent, and when the Cr content increases to 1.2 wt%, the κ Ⅲ phase appears core–shell structure. The strength and hardness of the alloy initially increase with the rise in Cr content, followed by a subsequent decrease. An optimal comprehensive performance is observed when the Cr content is 0.6 wt%, at which point an excellent combination of strength and ductility of the alloy is achieved