What makes Cu-W better than copper alone?
When an electrical contact opens under load, an arc forms between the separating contacts. The arc temperature can reach 5,000–20,000°C locally — far above the melting point of copper (1,085°C). A pure copper contact would melt, evaporate, and weld back together, causing contact failure and potential switchgear damage.
Tungsten's melting point (3,422°C) is the highest of any metal. By combining tungsten skeleton with copper infill, Cu-W contacts can withstand the arc energy without bulk melting. The copper phase conducts the current between arcing events and conducts heat away from the contact surface; the tungsten skeleton provides the arc-erosion resistance. The result is a contact material that can handle millions of operating cycles in vacuum circuit breakers, SF₆ switchgear, and high-current relays where standard copper or silver-based contacts would fail quickly.
Manufacturing routes: infiltration vs. liquid-phase sintering
There are two primary manufacturing routes for Cu-W contacts.
Infiltration: W powder is pressed into a porous skeleton (the 'perform') at typically 60–70% theoretical density, then sintered in hydrogen at 1,400–1,500°C to bond the W particles. The W skeleton is then placed in contact with solid copper or a copper-rich CuW preform and heated above the melting point of copper (1,085°C) in hydrogen. Liquid copper infiltrates the open pores of the W skeleton by capillary action. The result is a dense Cu-W composite at near-zero porosity. Infiltration is preferred for larger contact masses and allows independent control of W skeleton density and final Cu content.
Liquid-phase sintering: W and Cu powders are mixed, pressed, and sintered together above the Cu melting point. The liquid Cu phase promotes W skeleton densification. This route is used for smaller contact parts and produces comparable results to infiltration when W:Cu ratios and powder characteristics are tightly controlled. ASTM B702 covers wrought and P/M Cu-W contact materials, providing composition and property specifications for commercial grades (Cu-W 10/90, 20/80, 25/75, 30/70, 40/60 by wt%).
W powder requirements for Cu-W contact infiltration
The performance of the finished Cu-W contact depends critically on the W powder used to make the skeleton. Key parameters:
F.S.S.S. grain size: 1.5–8 µm is the typical range. Finer powder (1.5–3 µm) produces a higher-density W skeleton with smaller pores — the resulting Cu-W composite has lower Cu content and higher hardness. Coarser powder (4–8 µm) produces lower-density skeletons that absorb more copper during infiltration, giving higher Cu content, lower hardness, and better electrical conductivity but reduced arc-erosion resistance. The F.S.S.S. is selected based on the target Cu-W ratio of the finished contact.
Oxygen content: The most critical chemistry parameter for infiltration-grade W powder. Oxygen as surface WO₃ inhibits copper wetting during infiltration — high oxygen causes non-wetting of pores, leading to residual porosity in the contact body. Industry practice specifies W powder oxygen max. 0.05–0.08% (500–800 ppm) for reliable infiltration. Our standard grade: O max. 0.06%.
Iron content: Fe in W powder dissolves into the Cu-W structure during sintering and reduces electrical conductivity. Specify Fe max. 50–100 ppm for contact-grade W powder, verified by ICP-OES on the CoA.
Typical Cu-W grades and their applications
Cu-W contacts are specified by composition — the percentage of tungsten and copper by weight (or volume). Higher W content = harder, more arc-resistant; higher Cu content = better conductivity and easier machining.
Cu-W 10/90 (10% Cu, 90% W): Very high hardness (250–280 HV), low conductivity (~17% IACS), extreme arc erosion resistance. Used in heavy-duty oil-filled switchgear contacts, cathode sputtering targets.
Cu-W 20/80: Hardness 200–240 HV, conductivity 24–30% IACS. General-purpose vacuum circuit breaker contacts (12–40.5 kV class), high-voltage disconnectors.
Cu-W 25/75 to 30/70: Hardness 175–215 HV, conductivity 32–38% IACS. Vacuum interrupter contacts in medium-voltage switchgear (up to 40.5 kV), arc-discharge contacts in plasma torches.
Cu-W 40/60: Hardness 150–170 HV, conductivity 43–50% IACS. Lower-voltage contactors, circuit breakers (< 12 kV), EDM electrodes where machinability and conductivity are prioritised over arc erosion resistance.
Sourcing W powder for Cu-W contacts from India
India has grown as an alternative source for W powder for Cu-W contact manufacture, particularly as buyers in Europe, Korea, Japan, and Southeast Asia seek to reduce dependence on Chinese-origin W powder. Jayanth Tungsten (Tumkur, Karnataka) produces W metal powder in F.S.S.S. 1.5–15 µm with W min. 99.85%, O max. 0.06%, and Fe max. 50 ppm, documented on ICP-OES CoA.
Export documentation from India for W powder includes: commercial invoice, packing list, bill of lading, certificate of origin, SDS (GHS/REACH compliant), and CoA. HS code for W metal powder: 8101.94. Customs duty in most EU and Asian markets is 0–3% for non-Chinese origin W powder. Contact Jayanth Tungsten via WhatsApp for pricing, sample availability, and current lead time.