Guides / Materials

Non-Magnetic Tungsten Parts: Specifying and Machining W-Ni-Cu

Updated September 26, 2026 · Reviewed September 26, 2026

Magnetism is one of the easiest requirements to miss on a tungsten drawing, because the default grade most shops run is mildly magnetic. This guide explains why, what to specify when your part cannot be, and what shops need from your RFQ to get the right material on the first try.

Why standard tungsten heavy alloy is magnetic

Tungsten heavy alloy is 90 to 97% tungsten held together by a binder, most commonly nickel and iron, written as W-Ni-Fe. Iron is ferromagnetic, and even at the binder’s relatively small share of the total composition, it gives standard heavy alloy mild magnetism. This is irrelevant for most applications, counterweights, general shielding and ballast do not care whether the material is magnetic. It becomes a real problem for a specific category of use: anything near equipment sensitive to magnetic fields.

When magnetism actually matters

• MRI equipment, where any ferromagnetic material near the magnet can be pulled toward it or distort the imaging field, making magnetism a safety and functional issue rather than a cosmetic one.
• Magnetic sensors and instrumentation, where a nearby ferromagnetic mass can shift a sensor’s reading even at low field strength.
• Electron beam and certain semiconductor equipment, where stray magnetic fields from nearby materials can affect beam paths or process sensitivity.

If your part sits in any of these environments, or you are not sure whether it will, raise the question before the drawing goes out, not after a part is delivered and fails testing.

The non-magnetic alternative: W-Ni-Cu

Tungsten heavy alloy can also be made with a nickel-copper binder instead of nickel-iron, written as W-Ni-Cu. Copper is not ferromagnetic, so W-Ni-Cu heavy alloy is effectively non-magnetic while keeping density in a similar range to W-Ni-Fe, typically 17.0 to 18.0 g/cm³. It machines on the same CNC equipment with the same general approach as W-Ni-Fe, so switching to the non-magnetic grade does not change your process or tolerance expectations, only the material order.

Pure tungsten as a second option

Pure tungsten itself is non-magnetic, since it has no ferromagnetic binder at all. It is a reasonable choice when the application also needs the highest melting point of any metal alongside non-magnetic behavior, such as certain high-temperature fixtures near sensitive equipment. For most non-magnetic requirements, though, W-Ni-Cu heavy alloy is the more practical choice, since it machines more easily and is less prone to the chipping and cracking that pure tungsten’s brittleness causes.

Comparing the three non-magnetic-relevant grades

Grade	Typical density (g/cm³)	Magnetic behavior	Machinability
W-Ni-Fe heavy alloy	17.0 to 18.5	Mildly magnetic from iron content	Machines like hard cast iron, the easiest of the group
W-Ni-Cu heavy alloy	17.0 to 18.0	Effectively non-magnetic	Similar to W-Ni-Fe, same CNC process
Pure tungsten	Around 19.3	Non-magnetic	Brittle, chips and cracks more easily, often finished by grinding or EDM

W-Ni-Fe is included here as the reference point most buyers start from, and the grade to move away from once magnetism becomes a requirement.

How to specify it correctly

The most common mistake is assuming “tungsten heavy alloy” alone communicates the requirement. It does not; a shop defaults to whichever binder is standard for them, which is usually W-Ni-Fe. To get the non-magnetic grade reliably:

1. Write “W-Ni-Cu” explicitly on the drawing and RFQ, not just “heavy alloy” or “tungsten.”
2. State the reason, such as MRI proximity or sensor sensitivity, so the shop understands the requirement is functional, not a preference.
3. Ask for material certification if your application needs documented proof of the binder system used, which matters most in regulated or safety-critical environments.
4. Confirm density and mechanical properties if your part also has a structural or mass requirement, since W-Ni-Cu and W-Ni-Fe have slightly different property ranges within the same ASTM B777 class.
5. Consider magnetic permeability testing on the finished part if your application has a very low tolerance for any residual magnetic response, rather than relying on the material designation alone.

Common mistakes on non-magnetic tungsten drawings

• Writing “non-magnetic tungsten” without naming W-Ni-Cu. A note in the corner of the drawing is easy to miss. Put the binder system in the material callout itself.
• Specifying W-Ni-Cu only in the RFQ text, not on the drawing. If the drawing and the RFQ ever separate, for example when a shop forwards the drawing to their supplier, a requirement stated only in the RFQ can get lost.
• Assuming a past order was non-magnetic because it “seemed fine.” Without a stated binder and, where it matters, a permeability check, there is no way to confirm a part was actually W-Ni-Cu rather than W-Ni-Fe.
• Not budgeting extra lead time. W-Ni-Cu is less commonly stocked than W-Ni-Fe. If your schedule is tight, flag the non-magnetic requirement as early as possible so the shop can source it in time.

What shops ask when magnetism is not addressed in the RFQ

When an RFQ says only “tungsten heavy alloy” with no binder stated, a shop that stocks both systems will usually pause and ask before quoting:

• Does this part need to be non-magnetic, or is standard W-Ni-Fe acceptable?
• If non-magnetic, how is that verified: material designation alone, a certification, or a permeability test on the finished part?
• Is there a deadline that affects whether W-Ni-Cu can be sourced in time, given it is less commonly stocked than W-Ni-Fe?
• Does the part have a mass or density target that needs to hold across the switch from one binder to the other?

A shop that does not ask any of these and simply quotes in its default binder is not being careless, it is following the drawing as written. The responsibility for catching the requirement sits with the RFQ, not with the shop guessing correctly.

Tolerances and machining are unchanged

W-Ni-Cu heavy alloy does not require a different machining approach than W-Ni-Fe. It turns and mills on standard CNC equipment with the same carbide tooling, and holds the same typical tolerances of ±0.01 to ±0.025 mm on turned and milled features. Switching to the non-magnetic grade is a material decision, not a process change, so it should not meaningfully affect your quote’s timeline or the shop’s ability to hold your drawing’s tolerances.

What to include in the RFQ

1. Binder system stated explicitly, W-Ni-Cu rather than a general “non-magnetic” note.
2. The reason for the requirement, MRI proximity, sensor sensitivity or another functional driver.
3. Whether permeability testing on the finished part is required, and to what threshold if known.
4. Material certification requirements, if your application needs traceable documentation of the binder system.
5. Density or mechanical property requirements, if the part also carries a structural or mass function.

Getting the right material on your part

If your application needs a non-magnetic tungsten part, send your RFQ with W-Ni-Cu stated clearly, and we match it with shops that stock or source that binder system. For the class structure that applies to both binder systems, see ASTM B777 tungsten heavy alloy classes. For the mechanics of heavy alloy machining in general, see tungsten heavy alloy machining.

See also: magnetic vs non-magnetic tungsten alloys, for the ASTM B777 permeability limit and test methods.

Frequently asked questions

Sources

• ASTM B777 - Standard Specification for Tungsten Base, High-Density Metal
• Wikipedia - Tungsten heavy alloy
• Wikipedia - Ferromagnetism

Keep reading

• Molybdenum Copper or Tungsten Copper: Choosing a Heat Spreader Material
• Doped Tungsten: Lanthanated and Potassium Doped Grades and Their Parts