Tungsten copper cannot be cast. The two metals are practically insoluble in each other in the solid state, form no intermediate compounds, and their melting points are almost 2,600 °C apart — so there is no alloy melt to pour. Every tungsten-copper electrode in existence is a powder-metallurgy product, and the route that dominates industrial production of the common electrode grades is skeleton sintering plus copper infiltration. Understanding that route explains most of what separates a good CuW billet from a mediocre one, and it is the process behind every wheel and rod we ship.
Why infiltration, specifically
For tungsten contents above roughly 60%, Chinese industry sources describe infiltration as effectively the only viable production route: direct liquid-phase sintering of mixed W and Cu powders struggles to densify copper-poor compositions. The trick is to stop trying to consolidate both metals at once. Instead:
- Press pure tungsten powder into a shape with deliberately connected porosity.
- Sinter that skeleton until the tungsten particles weld to each other — strong enough to survive handling, porous enough to drink molten copper.
- Place the skeleton against a weighed copper block in graphite tooling and heat everything, in hydrogen or vacuum, past the melting point of copper (practical temperatures run roughly 1,100–1,400 °C).
- Let capillary pressure pull the melt through the connected pore network until the skeleton is full.
The result is a near-fully-dense two-phase composite: a rigid tungsten matrix with copper filling it like water in a sponge. No alloying, no intermetallics.
The parameters that decide the outcome
Skeleton relative density is the master variable. It fixes how much copper the billet takes — and with it the composition, conductivity and hardness. Chinese batch-stability studies of infiltrated W-Cu treat skeleton density as a designed value held to within about half a percent across powder lots, because drift in the skeleton drifts every property downstream.
Tungsten powder grain size sets the sintering behavior: coarser powder needs a higher sintering temperature to reach the same skeleton density, so powder grade and furnace schedule have to be qualified together, not chosen independently.
Infiltration temperature and wetting. Molten copper wets tungsten well — near-perfectly at the upper end of the infiltration range — and capillary force does the filling work. Too low a temperature leaves the melt sluggish and pores unfilled; too high, and the copper’s surface tension falls until it bleeds back out of the skeleton, while trapped gas in closed pores expands and disrupts the structure.
Copper charge weight. Charging slightly more copper than the theoretical pore volume ensures the skeleton fills completely rather than starving at the far end.
Where the defects come from
Residual porosity is the signature defect of a badly run infiltration line, and it has three known causes worth knowing as a buyer:
- Closed pores in the skeleton. Once the sintered skeleton passes roughly 80% relative density, pores begin to close off and copper can no longer reach them. That is why electrode-grade skeletons are designed below that threshold.
- Solidification shrinkage. Copper shrinks as it freezes inside a skeleton with a very different thermal expansion. The last metal to solidify can leave shrinkage cavities, typically toward the ingate side.
- Poor wetting in fine pores. Where capillary radius gets small, wetting force may not beat the melt’s own constraints, leaving un-infiltrated spots.
Porosity is not cosmetic: it shows up in service as lowered conductivity, premature face erosion on a welding wheel, and arcing damage on an EDM electrode.
What a buyer should actually check
The checks are simple because the failure mechanisms are simple:
- Density by displacement. Weigh the part, measure its volume, compare with the grade’s published density. Porosity reads light; nothing else on the floor catches a poorly infiltrated billet faster. Our W/Cu 75/25 runs ≈ 15.2 g/cm³ typical and 70/30 ≈ 14.5 g/cm³.
- Composition against the grade. W 75% ±2% or 70% ±2%, balance copper — on the mill certificate, not just the quotation.
- Internal soundness. Ultrasonic inspection is standard practice in Chinese high-reliability W-Cu production precisely because infiltration defects are internal. For critical wheels, ask whether the batch was tested.
- Batch consistency. Ask how the supplier controls incoming tungsten powder. Batch-to-batch drift in CuW almost always starts at the powder lot, which is why mature producers qualify powder suppliers, not just furnace schedules.
Our own production runs exactly the route described here — press, sinter, infiltrate, then finish-machine — with every batch checked for composition, density and hardness, and third-party test reports to ASTM B702 available on request.
Why the process matters to your part
Because infiltration builds the composite as a near-net billet, large one-piece parts are practical: our line carries shapes up to 400 mm OD × 100 mm thickness — the size class big seam-welding wheels need. And because infiltration sets the grade, switching between W/Cu 75/25 and W/Cu 70/30 is a production decision on the same line: wheel geometry, tolerances (OD 0/+0.5 mm, bore H7, runout 0.02 mm) and machining stay identical. Reading the resulting properties on a datasheet is covered in our CuW properties guide.
Get a quote
If you need wheels, rods or custom infiltrated parts, request a quote with your drawing — standard shapes ship in 10–14 days with no minimum order, and we will tell you plainly which grade the process data supports.