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Below is a “from‑scratch” permanent‑magnet concept that stitches together the best lessons from tetragonal Fe‑Co physics, rapid ordering tricks, and exchange‑spring nanocomposites. I kept every element earth‑abundant, readily recyclable, and friendly to mass‑production metallurgy.
Target | Value | Rationale |
|---|---|---|
Uniaxial anisotropy | ≥ 1 MJ m⁻³ | at least ferrite‑class coercivity |
Saturation induction | ≥ 2 T | push remanence beyond 1.5 T |
(BH) | 30 – 40 MGOe | close the gap to Nd‑Fe‑B mid‑grade grades |
Curie temperature | ≥ 550 °C | EV‑motor safe margin |
No critical elements | Fe, Co, V, N, B, Cu | price < $ 10 kg⁻¹ |
FeCoVNB Body‑centred tetragonal Fe‑Co‑V‑N (c/a ≈ 1.22)
V + N stabilise the bct lattice and lock in even in 100 nm films and bulk foils.
Pure bct‑FeCo is predicted to rival or exceed FePt’s anisotropy while carrying 50 % more magnetisation.
Fe‑Co‑B (bcc) shells 3–5 nm thick around each hard grain
Give an extra 0.4–0.5 T to through exchange‑spring coupling.
B lowers grain‑boundary mobility, freezing grain size near 20 nm.
Cu/VC nano‑precipitates (<2 vol %) form during aging and immobilise domain walls.
Induction melt Fe‑Co‑V master alloy, over‑doped with 0.5 wt % B.
Gas‑atomise into ≤ 30 µm powder; high quench rate preserves metastable bct nuclei.
Reactive nitriding: NH flow, 450 °C, 30 min → N uptake, full tetragonality.
Surfactant‑assisted ball mill 2 h → 15–25 nm crystallites.
Spark‑plasma sinter + 2 T field: 550 °C, 5 min → dense, c‑axes aligned bulk.
Age 400 °C, 1 h → Cu/VC precipitates and stress relief.
Passivate (phosphate dip or Al 99.5 % vacuum coating).
Every step is conventional powder‑metallurgy equipment; cycle time < 2 h.
Parameter | Estimate | How we get there |
|---|---|---|
2.0 – 2.1 T | bct Fe‑Co base + 30 % soft phase | |
1.2 – 1.5 MJ m⁻³ | V + N tetragonality | |
0.9 – 1.1 T | single‑domain grains ≈ 20 nm + precipitate pinning | |
1.5 – 1.7 T | exchange‑spring boost | |
(BH) | 32 – 40 MGOe | micromagnetic modelling & scaling law from nanocomposites |
~900 K | high‑FeCo matrix |
That slots the alloy squarely between MnAlC (≈8 MGOe) and today’s mid‑range Nd‑Fe‑B (35–45 MGOe)—without Dy, Nd or Sm.
Element | Job |
|---|---|
Fe + Co | delivers the world‑record saturation magnetisation of FeCo |
V | expands the c‑axis and helps lock the bct lattice |
N (interstitial) | amplifies tetragonality and Ku while slightly boosting resistivity |
B | glass‑former; refines grains; bumps resistivity; part of soft shell |
Cu | forms nanoscale precipitates that immobilise domain walls without diluting Ms |
XRD (Cu Kα) to confirm c/a > 1.2 after nitriding.
TEM + EELS grain‑size and phase mapping.
VSM loops @ 300 K for & .
Pulsed‑field testing to 10 T for irreversible field.
High‑T ageing (up to 200 °C for 1000 h) to benchmark thermal demagnetisation.
If loops match the table above, scale gas‑atomisation to 50 kg lots and feed existing powder‑bed fusion printers for net‑shape motor rotors.
A tetragonal Fe‑Co‑V‑N hard phase exchange‑coupled to Fe‑Co‑B soft shells should hit ~35 MGOe with nothing rarer than vanadium, survive 500 °C, and roll straight off a powder‑metallurgy line. That’s a permanent magnet worth chasing—and far more promising than cubic Fe(B,C) or W‑doped variants.