Novel Fe–Ni–Si alloys with a balanced property set for electrical machines

Alloys that simultaneously exhibit good magnetic properties, high mechanical strength, and elevated electrical resistivity are critical for next-generation high-speed, high-torque electrical machines used in electric mobility and energy systems. The development of such novel alloys requires a balanced property set. However, binary Fe–Si and Fe–Ni alloys do not possess the desired combination of mechanical, magnetic and electrical properties. In earlier work, promising regions and compositions in the ternary Fe–Ni–Si system were identified via high throughput screening. Based on the results, we studied in this work a promising high-Ni–Si region (35–40 wt% Ni, 6–10 wt% Si) and a relatively low-solute composition, Fe–11.5Ni–2.7Si, using directed energy deposition and arc melting, to decouple compositional and processing effects. High-Ni–Si alloys exhibited extensive intergranular intermetallic network formation, resulting in high hardness but severe embrittlement. In contrast, Fe–11.5Ni–2.7Si stabilized as a single-phase BCC matrix and exhibited an attractive combination of properties: yield strength of 551 MPa, ultimate tensile strength of 709 MPa, elongation of 4.8%, resistivity of 105 μΩ cm, saturation magnetization of 199 emu/g and coercivity of 14 Oe. These results identify Fe–11.5Ni–2.7Si as a novel Fe–Ni–Si alloy composition that balances mechanical, electrical, and magnetic performance. These results demonstrate that intermetallic phase fraction and connectivity govern the trade-off between mechanical, magnetic, and electrical properties. Controlling phase architecture through composition and processing provides a viable design strategy for multifunctional magnetic structural alloys.