Motor lamination materials: NOES vs cobalt-iron vs nickel-iron (selection guide)

1. Short answer: when each material usually wins

Forget the datasheet for a moment. Picture your motor first.

Use NOES when:

• Speed is moderate to high, but not extreme (line frequency up to a few hundred Hz electrical, maybe low kHz with thin gauge)
• Peak flux density in tooth/back iron can stay around ~1.5–1.7 T in operation
• You care about cost per kW and per unit more than squeezing the last 3–4% torque density
• You want a lamination supply chain that already exists everywhere

NOES remains the default core material for most motors and generators because it combines high magnetic saturation, reasonable losses, and low cost, especially when rolled to 0.5–0.2 mm thickness and alloyed with ~0.5–3.5 wt% Si and Al.

Use cobalt-iron when:

• The motor is volume- or mass-constrained and you need serious power density
• You’re designing for high peak flux densities (1.9–2.2 T in normal use, with margin)
• Operating temperature is high and constant performance across the range matters
• Aerospace, motorsport, high-speed starter-generators, magnetic bearings, flywheel rotors and similar cases

Iron-cobalt alloys are at the top in saturation magnetization, around 2.3–2.4 T for typical 35–50 % Co alloys such as Hiperco-type grades, with high Curie temperature.

You are paying almost purely for higher B_sat and thermal headroom.

Use nickel-iron when:

• Extremely high permeability is more important than high B_sat
• You operate at relatively low flux densities and want ultra-low losses, low coercivity
• You’re building sensors, resolvers, torque transducers, precision actuators, special machines, not a mainstream traction motor

High-nickel Ni-Fe (~79–80 % Ni) gives very high initial and maximum permeability and very low hysteresis losses, but saturation induction is only about 0.8–1.0 T.

Medium-nickel (~40–50 % Ni) alloys sit around 1.5–1.6 T saturation with good permeability – more interesting when you still need some torque density.

2. Quick comparison table (for motor lamination stacks)

Typical values, not a datasheet. Think of them as design “zones”.

Use this table as a sanity check. If your use-case doesn’t sit anywhere near the “typical roles” row, rethink the material choice.

3. What actually drives the choice (before talking materials)

Most teams jump straight into “Is cobalt-iron worth it?”. A better order:

1. Flux density window
   • Set the maximum tooth/back-iron flux density the design will see at worst-case operating point.
   • Decide how close to saturation you are comfortable running (e.g. 1.6 T vs 1.9 T).
   • That limit alone often tells you whether NOES is enough.
2. Frequency & waveform
   • Mechanical speed × pole pairs gives electrical frequency; include field-weakening and overspeed.
   • For drives with lots of harmonic content, treat the loss budget as “effective higher frequency” even if f_fundamental is modest.
3. Thermal and efficiency targets
   • Define allowable core loss as a percentage of copper loss at key points of the torque-speed curve.
   • This gives you a W/kg target for lamination stacks, which tells you how thin and which alloy to consider.
4. Cost per kW, not cost per kg
   • High-saturation materials can cut back iron and tooth width, sometimes shrinking overall stack length.
   • Compare cost per kW of output, not per kilogram of strip.
5. Manufacturing route and volumes
   • Stamping vs laser vs fine blanking vs bonding.
   • Available annealing capacity (hydrogen, vacuum, batch vs continuous).
   • Tolerance of your stack-assembly method to stress-sensitive alloys.

Once this is pinned down, the NOES / Co-Fe / Ni-Fe decision is usually much less “mystical”.

4. NOES: the workhorse with a surprisingly wide comfort zone

You already know the basics: Fe-Si alloy, ~0.5–3.5 % Si (plus Al), isotropic in-plane properties, rolled and coated for rotating machinery.

What matters in practice:

4.1 Frequency vs thickness

• For EV traction and high-speed industrial drives, thin-gauge NOES (<0.25 mm, sometimes ~0.20 mm or even 0.15 mm) can cut core losses significantly by reducing eddy currents.
• The trade-off is:
  • Lower stacking factor (more coating, more air)
  • Harder stamping, tighter flatness control
  • Higher strip price per kg

High-speed automotive motors have already moved from 0.35 mm toward 0.27–0.30 mm and thinner gauges for lower iron loss; this trend is well documented in traction motor materials articles.

If your electrical frequency is below ~400 Hz and efficiency targets aren’t extreme, a good grade of 0.35 mm NOES often meets the spec with far less pain.

4.2 Flux density and margin

• Most modern NOES grades can support flux densities around 1.5–1.7 T in the motor under load before you start getting nervous about saturation and excess loss.
• Push beyond that and you’ll see rising hysteresis and a stronger link between small tolerancing errors (e.g. tooth fillets, misalignment) and local saturation.

So if your electromagnetic model demands >1.8 T in teeth at peak torque, you’re in cobalt-iron territory or re-geometry territory.

4.3 When NOES is “good enough”

Typical cases where NOES lamination stacks are still the rational choice:

• Standard industrial induction motors and synchronous motors
• Many EV traction motors where the platform prioritizes cost over absolute kW/kg
• Generators with more room in the envelope
• Applications where acoustic noise and vibrations matter more than squeezing saturation

In short: if you can meet torque, efficiency, and temperature with NOES, moving to a more exotic alloy needs a hard financial justification.

5. Cobalt-iron: buying flux density with cash and processing complexity

Iron-cobalt alloys are the heavy artillery. High B_sat (often ~2.35–2.4 T), high Curie temperature, decent permeability.

5.1 What you actually get

• Higher torque density At the same current and copper, you can run higher peak induction in teeth and back iron without saturating, so you can shorten tooth width and stack length, or increase torque for same volume.
• Better high-temperature behavior Higher Curie temperature keeps magnetic properties useful at elevated operating temperatures where NOES starts to degrade faster.
• Often thinner gauges Many Fe-Co strip products are supplied in thin sections (≤0.20 mm), which also helps core losses at higher frequency.

So, flux density and temperature margin. That’s what you’re paying for.

5.2 What it costs (beyond the price list)

The obvious cost: cobalt is expensive and volatile. The less obvious costs:

• Processing and stress sensitivity
  • Edges, burrs, and stamping strain hurt magnetic performance.
  • You may need careful annealing (sometimes hydrogen or vacuum) after punching to recover B_sat and permeability.
• Mechanical considerations
  • Strong but more rigid; crack initiation at notches is a concern in high-speed rotors.
  • Stack assembly methods (welding, bonding, riveting) need to be checked for added stress and local heating.
• Supplier base
  • Fewer mills produce Fe-Co strip compared to NOES, so qualification and dual-sourcing take longer.

5.3 When cobalt-iron actually earns its keep

Situations where Fe-Co laminations are usually justified:

• Weight-critical aerospace machines (starter-generators, actuation motors)
• Motorsport and high-end racing e-drive units
• High-speed generators and magnetic bearings where rotor diameter is constrained and surface speed is extreme

Common design pattern:

Use cobalt-iron where flux density is highest (e.g. rotor, tooth tips) and NOES elsewhere, if your lamination stack supplier can manage hybrid stacks and compatible annealing routes.

If you’re considering Fe-Co solely because “others in the segment are using it”, double-check the flux map. The gain might be marketing, not electromagnetics.

6. Nickel-iron: precision material, not a general traction material

Nickel-iron alloys are broad family. They aren’t all the same, and that matters.

6.1 Two main families for laminations

1. High-nickel (~78–80 % Ni, “Permalloy”, “Mu-metal”)
   • Extremely high permeability (μ_r up to 10⁵+ in optimized states)
   • Very low coercivity and hysteresis loss at low flux density
   • Saturation around 0.8–1.0 T; not friendly for traction motors
2. Medium-nickel (~40–50 % Ni)
   • Higher saturation (often >1.5 T) with still-good permeability
   • Useful when you need more torque density than high-Ni alloys allow, but still want better magnetic performance than NOES at specific operating points.

Both groups are available as strip, sheet, and tape-wound core feedstock, and both see more use in transformers, sensors, shielding, and instrumentation than in main traction rotors.

6.2 Processing caveats

With Ni-Fe, the process can make or break the part:

• Properties are highly sensitive to annealing atmosphere and cycle (hydrogen, vacuum, time, temperature).
• Many high-Ni materials are relatively soft mechanically and can pick up damage during stamping or stacking.
• For laminated motor cores, you need a lamination supplier with real Ni-Fe experience; trial-and-error here is expensive.

6.3 Where Ni-Fe lamination stacks belong

Common, sensible use-cases:

• Torque sensors and resolvers where flux control and linearity matter more than torque density
• Instrument transformers and signal transformers
• Stator segments in motors that operate at low induction but demand extremely low magnetizing current or low noise in control loops
• Magnetic shielding and flux concentrators embedded into machines

If your 200 kW traction motor concept is “entirely nickel-iron lamination stacks”, something is off.

7. How lamination stack manufacturing changes the answer

Material choice without process thinking is half a decision.

Key process-material interactions for B2B lamination stack projects:

7.1 Stamping vs laser cutting

• Stamping
  • Lower per-piece cost at volume.
  • Introduces mechanical stress and burrs; sensitive alloys (Fe-Co, high-Ni) need good die design and stress-relief annealing.
• Laser cutting / waterjet / wire EDM
  • Great for prototypes and small series.
  • Local heat-affected zones can degrade magnetic properties unless properly annealed afterward.

For NOES, stamping + a reasonable anneal is usually sufficient. For Co-Fe and high-Ni, discuss with your lamination supplier how they restore properties after cutting.

7.2 Stack assembly: interlock, welding, bonding

Each method adds its own “penalty”:

• Interlocking
  • Good for NOES; minimal extra heat.
  • For stiff Fe-Co, deep interlocks can act as stress concentrators.
• Laser / TIG welding
  • Local heating can hurt core loss and permeability near the weld; more serious with Co-Fe and Ni-Fe.
• Bonded stacks (self-bonding coatings or glue bonding)
  • Very attractive for high-speed rotors (good hoop strength, low noise).
  • Requires compatible coatings and process temperatures for the alloy.

When you send a lamination stack RFQ, include the material + thickness + assembly method as a coupled decision, not separate checkboxes. That’s where many “we picked Fe-Co but saw no gain” stories come from.

8. Example selection scenarios

Some quick sketches – not full designs, but enough to anchor material choice.

8.1 150 kW EV traction motor, 18 000 rpm max

• Envelope: standard automotive e-axle, space tight but not extreme
• Efficiency: OEM wants ≥96% peak
• Cooling: oil spray onto stator, rotor mostly air-cooled

Likely outcome:

• High-grade, thin-gauge NOES around 0.20–0.27 mm for both stator and rotor
• Work mainly on tooth geometry, skew, and slot fill before considering Fe-Co
• Fe-Co rotor only if simulations show clear torque/efficiency advantage and the cost model supports it

8.2 50 kW starter-generator for aerospace

• Weight very limited; envelope fixed
• High altitude, high ambient temperature
• Long periods at high speed

Here, cobalt-iron starts to look like the “standard” option:

• Co-Fe stator and rotor laminations, thin strip
• Careful design for mechanical stresses and secure bonding or welding of the stack
• NOES would probably require a physically larger machine to reach the same continuous rating

8.3 Resolver for servo drive or traction motor

• Very low signal levels
• Tight linearity and phase accuracy constraints
• Size modest; torque density irrelevant

Typical outcome:

• High-nickel Ni-Fe laminations or tape cores for rotor/stator
• Strip-wound or stamped, then annealed to maximize permeability and minimize hysteresis
• NOES here would be cheaper but may not meet the signal quality requirements.

9. Practical checklist for your RFQ to a lamination stack supplier

When you send an RFQ to a B2B lamination stacks manufacturer, the fastest way to a sensible quote is to phrase your needs in terms that connect directly to material selection:

• Target material family: NOES / Fe-Co / Ni-Fe (and if flexible, rank them)
• Operating frequency range and max mechanical speed
• Max flux density in tooth and back iron from your FEA (peak and RMS)
• Allowed core loss (W/kg) at one or two representative operating points
• Lamination thickness preference or constraints
• Planned stack assembly method (interlock, bonding, welding, etc.)
• Whether post-processing anneal is possible in your supply chain
• Expected annual volume (this changes the stamping vs laser trade-off)

A good lamination specialist will then propose specific grades (e.g. named NOES grade, a particular Fe-Co alloy, or a Ni-Fe composition) and thicknesses that match these constraints.

10. FAQ: motor lamination material choices

Summary

Pick the lamination material by starting from your flux density, frequency, thermal, and cost targets. In many cases, optimized NOES lamination stacks are still the rational default. Cobalt-iron and nickel-iron step in only when a specific, quantifiable requirement pushes you outside NOES’ comfort zone.

Once that is clear, the rest is just implementation detail: thickness, coatings, and how you turn strip into a rotor or stator stack that behaves the way your FEA promised.