Pure tungsten and tungsten copper both belong in a modern welding shop — but in different places. Specifying pure tungsten where a CuW alloy belongs is one of the most common (and most expensive) material mistakes in resistance welding. This guide explains the physics behind the difference and gives you a simple decision rule.
The core physics
Pure tungsten (99.9% W) is a refractory metal: it keeps strength at temperatures where copper electrodes would melt. But it conducts only about 30% IACS, and its high modulus plus brittleness mean it is vulnerable to thermal fatigue cracking — repeated heating and cooling cycles open up grain-boundary cracks, and particles of tungsten then spall off onto the weld.
Tungsten copper (W/Cu 75/25 or 70/30) is a composite, not an alloy in the strict sense: a rigid, sintered tungsten skeleton infiltrated with copper. The tungsten skeleton provides hardness and erosion resistance; the copper phase does two jobs the pure metal cannot:
- Conducts the welding current — 38–45% IACS, meaning less resistive heating in the electrode face for the same schedule.
- Pumps heat out — the copper continuously conducts welding heat away to the cooled shank, so the face runs hundreds of degrees cooler in duty-cycle service.
The failure mode changes accordingly: instead of cracking and spalling, a CuW electrode’s face slowly dresses and re-trues — a maintenance event, not a scrap event.
Side-by-side
| Property (typical) | Pure W | W/Cu 75/25 | W/Cu 70/30 |
|---|---|---|---|
| Density | 19.3 g/cm³ | ≈ 15.2 g/cm³ | ≈ 14.5 g/cm³ |
| Conductivity | ~30% IACS | ≥ 38% IACS | ≥ 42% IACS |
| Hardness | 60–70 HRC | 85–95 HRB | 80–90 HRB |
| Thermal cycling behaviour | Cracks, spalls | Stable face | Stable face |
| Typical duty | TIG/PLASMA tips, high-temp fixtures | Resistance welding electrodes & wheels | High-current projection welding, heat sinks |
Where pure tungsten belongs
- TIG and plasma electrodes — the arc runs on the tungsten itself; here its refractoriness is the point.
- High-temperature fixtures and supports inside furnaces, where there is no current to conduct.
- Resistance-brazing dies for very high-temperature work where even CuW softening is a concern.
Where tungsten copper belongs
- Seam welding wheels — the copper phase keeps the face cool across millions of inches of seam. See seam welding wheel applications.
- Spot and projection welding electrodes — current density plus thermal cycling is exactly the job CuW was designed for. More on resistance welding electrodes.
- EDM electrodes — pure tungsten erodes slowly but machines poorly; CuW combines acceptable erosion with real manufacturability. See EDM electrode applications.
- Heat sinks and electrical contacts where thermal resistance matters as much as strength — see heat sink applications.
The decision rule
Ask one question: does the electrode carry welding current while being thermally cycled?
- Yes → tungsten copper. Pure tungsten’s brittleness and low conductivity will cost you electrode life and weld consistency.
- No → pure tungsten may be right; it is simply not a product we manufacture.
Note on our catalogue: ArcTung deliberately supplies the two workhorse ratios, W75Cu25 and W70Cu30, as stocked, fully machinable material — plus rods, blocks and threaded forms in both. Concentrating on two ratios keeps both available ex-stock with a 10–14 day standard lead time and no minimum order.
Common questions
Is CuW harder to machine than pure tungsten? The opposite. Pure tungsten is notorious — it is machined by grinding and EDM more than by cutting. Infiltrated CuW cuts like a hard bronze on conventional tooling.
Does the copper melt out at welding temperatures? No. The copper is held in a continuous tungsten skeleton; at 900 °C the composite still retains useful hardness, which is why CuW is specified against softening rather than melting.
Can I get certified mechanical data? Yes — typical values are published on each product page, and stamped third-party test reports to ASTM B702 can be ordered with your shipment on request.
Get a quote
If you are currently consuming pure tungsten electrodes in a resistance welding role, send us the drawing — request a quote and we will tell you honestly whether a CuW equivalent would run better or worse, with pricing valid 7 days.