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<p>Binary FeCo soft magnetic alloys possess high magnetic properties but suffer from extremely brittleness, which restricts their application in high-speed motor rotors. For the FeCo soft magnetic alloy system, all doping elements face the challenge of balancing strength, ductility, and magnetic properties. In this study, first-principles calculations were conducted to clarify the effects and underlying mechanisms of five dopant elements (V, Nb, Ta, Mo, and W) on the mechanical and magnetic properties of body-centered cubic (BCC) FeCo alloys. According to the&#xa0;calculation results, for mechanical properties, an optimal composition of combining V’s strengthening effect (Young's modulus&#xa0;<i>E</i> increases by 4.63%) with Nb’s enhancement of ductility (Poisson's ratio&#xa0;<i>ν</i> increases by 2.67%) at a doping amount of 1.85at% was obtained. For magnetic properties, all five doping elements lower the alloy’s atomic magnetic moment: Mo produces the smallest decrease coefficient of 0.035 <i>μ</i><sub><i>B</i></sub>/at.% compared with ~ 0.04 <i>μ</i><sub><i>B</i></sub>/at.% of other dopants. The Density of states (DOS) and Crystal Orbital Hamilton Populations (COHP) results reveal that V forms the strongest covalent bonds with the host atoms, even exceeding Fe-Co bonds, thereby enhancing alloy strength even at low concentrations, while low-modulus Nb/Ta element improves ductility compared with high-modulus Mo/W element. Regarding the magnetic properties, calculations of atomic magnetic moments and DOS reveal that all dopant atoms spin have opposite orientations to those of Fe and Co, resulting in decreased magnetic moments. To bridge the gap between ideal solid-solution models and experimental precipitation behavior, we further calculated pseudo-binary phase diagrams using CALPHAD methods and evaluated precipitation driving forces through formation enthalpies of competing secondary phases. Results reveal that Nb and Ta exhibit the strongest precipitation tendencies forming Laves phases, while V, Mo and W show moderate precipitation. These precipitates may enhance mechanical strength but potentially degrade soft magnetic performance by increasing coercivity. The proposed strategy in this work provides a promising route to address the challenge of brittleness in FeCo systems, offering a favorable balance between enhanced ductility and the retention of high magnetic induction at minimal doping concentrations.</p>

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First-principles investigation of the mechanical-magnetic properties trade-off in FeCo alloys: the role of V, Nb, Ta, Mo, and W dopants

  • 期刊论文

  • 发表日期：

    2026年4月7日

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  • Hang Yang,
  • Ya-Feng Zhang,
  • Qi-Yao Geng,
  • Cheng-Sen Ji,
  • Qiang Zheng,
  • Juan Du

摘要

Binary FeCo soft magnetic alloys possess high magnetic properties but suffer from extremely brittleness, which restricts their application in high-speed motor rotors. For the FeCo soft magnetic alloy system, all doping elements face the challenge of balancing strength, ductility, and magnetic properties. In this study, first-principles calculations were conducted to clarify the effects and underlying mechanisms of five dopant elements (V, Nb, Ta, Mo, and W) on the mechanical and magnetic properties of body-centered cubic (BCC) FeCo alloys. According to the calculation results, for mechanical properties, an optimal composition of combining V’s strengthening effect (Young's modulus E increases by 4.63%) with Nb’s enhancement of ductility (Poisson's ratio ν increases by 2.67%) at a doping amount of 1.85at% was obtained. For magnetic properties, all five doping elements lower the alloy’s atomic magnetic moment: Mo produces the smallest decrease coefficient of 0.035 μB/at.% compared with ~ 0.04 μB/at.% of other dopants. The Density of states (DOS) and Crystal Orbital Hamilton Populations (COHP) results reveal that V forms the strongest covalent bonds with the host atoms, even exceeding Fe-Co bonds, thereby enhancing alloy strength even at low concentrations, while low-modulus Nb/Ta element improves ductility compared with high-modulus Mo/W element. Regarding the magnetic properties, calculations of atomic magnetic moments and DOS reveal that all dopant atoms spin have opposite orientations to those of Fe and Co, resulting in decreased magnetic moments. To bridge the gap between ideal solid-solution models and experimental precipitation behavior, we further calculated pseudo-binary phase diagrams using CALPHAD methods and evaluated precipitation driving forces through formation enthalpies of competing secondary phases. Results reveal that Nb and Ta exhibit the strongest precipitation tendencies forming Laves phases, while V, Mo and W show moderate precipitation. These precipitates may enhance mechanical strength but potentially degrade soft magnetic performance by increasing coercivity. The proposed strategy in this work provides a promising route to address the challenge of brittleness in FeCo systems, offering a favorable balance between enhanced ductility and the retention of high magnetic induction at minimal doping concentrations.