Silver tungsten vs silver nickel contacts: how to choose

The short answer

Choose silver nickel when contact resistance, cost and ease of joining matter most and the arc energy is moderate. Choose silver tungsten when the contact has to survive high current, frequent arcing or a strong tendency to weld, and when the design can supply the extra force and the heat path that the material needs.

The two materials are not adjacent points on a single scale. Silver nickel is a conductive silver matrix with nickel particles. Silver tungsten is a refractory tungsten skeleton filled with silver. One behaves like a metal with hard inclusions. The other behaves like a ceramic frame with a conductive filler. That structural difference explains almost every performance difference below.

How each material is made

Silver tungsten is usually made by pressing tungsten powder into a skeleton, sintering it, and infiltrating the pores with molten silver. The result is a two-phase material with a continuous tungsten network and silver in the gaps. Grades are quoted by weight, commonly 50/50, 60/40 or 70/30 tungsten to silver. Higher tungsten means more erosion resistance and higher resistance.

Silver nickel is made by powder metallurgy: silver and nickel powders are mixed, pressed and sintered, sometimes with a controlled oxidation step. Common grades are 90/10 and 80/20. The nickel stays as discrete particles in a silver matrix, so the silver phase remains continuous and the material keeps a low resistance.

The manufacturing route affects the surface. Silver tungsten can develop a tungsten-rich surface after machining or arcing, which raises resistance. Silver nickel can develop a nickel-rich surface under certain conditions, but the effect is smaller. Both need a clean, oxide-free face at assembly.

Contact resistance and heat

Silver nickel has the lower contact resistance of the two, closer to fine silver than to silver tungsten. The continuous silver matrix gives current a low-resistance path, and the nickel particles are conductive enough not to block it. That is why silver nickel is common in relays and small breakers where the voltage drop across the contact matters.

Silver tungsten has a higher resistance because the tungsten network is resistive and because the real contact area is smaller for a given force. The material is harder, so it does not conform to the mating surface as readily. The result is a higher constriction resistance and more local heating at the same current.

Higher resistance is not automatically a problem, but it changes the thermal design. A silver tungsten contact needs a shorter thermal path to the carrier, a larger contact face or a higher force to keep the temperature rise within the limit. If the design has no room for any of those, silver tungsten will run hotter than the silver nickel part it replaced.

Arc erosion and welding

Silver tungsten is the stronger material under arcing. The tungsten skeleton has a high melting point and resists the molten bridge that forms when contacts open. Material loss per operation is lower, and the face keeps its shape for longer. It also resists welding because the molten metal bridge is weaker and the tungsten network breaks it.

Silver nickel erodes faster under high energy. The silver matrix melts and transfers, and the face can pit deeply. Under high inrush, the contacts can weld because the molten silver bridge is strong and the nickel particles do not interrupt it. The risk rises with capacitive loads, lamp loads and motor starting.

At low and moderate energy, the difference is smaller. A relay switching a few amps may never generate enough arc energy to show the gap between the two. The choice then turns on resistance, cost and the joining method rather than on erosion.

Force, bounce and mechanical design

A harder contact material needs more force to establish a stable contact spot. Silver tungsten has a smaller real contact area at the same force, so the constriction resistance is higher and the local temperature is higher. Increasing the force reduces both, but it also increases the spring stress and the energy at impact.

More force at impact usually means more bounce unless the spring and the damping are designed for it. Bounce is a problem because it produces a series of short arcs at make, which erodes the face and can weld it. A silver tungsten contact on a spring designed for silver nickel may bounce more, not less, because the higher force comes with a higher impact velocity.

The practical answer is to design the spring and the contact together. Set the force from the resistance and temperature target, then check the impact velocity and the bounce time. If the spring cannot supply the force without excessive bounce, silver tungsten is the wrong choice for that mechanism, regardless of its erosion performance.

Cost and availability

Silver nickel usually has the lower material and processing cost. It contains more silver by weight in the common 90/10 grade, but it is easier to sinter, roll, machine and join. Silver tungsten contains less silver in a 50/50 grade, but tungsten powder, sintering and infiltration are expensive, and the material is hard to machine, so it is often supplied as a brazed assembly.

Price per kilogram is the wrong comparison. Compare cost per operation over the life of the contact, including the carrier, the joining process and the scrap rate. A silver tungsten tip that lasts five times as long can be cheaper even at twice the piece price, provided the force and thermal design do not add cost elsewhere.

Availability also matters. Silver tungsten is a specialist material with fewer suppliers and longer lead times. If the programme needs a second source, check that both suppliers use the same grade and infiltration route, because a change in microstructure can change erosion behaviour.

A practical selection sequence

Start with the electrical duty. Write down the current, voltage, load type, inrush, time constant and the number of operations. Then estimate the arc energy per operation and the acceptable erosion allowance. That tells you whether the application is in silver nickel territory or needs a refractory material.

Next, check the mechanism. Can the spring supply the force the harder material needs without excessive bounce? Is there room for a larger face or a shorter thermal path? If the answer is no, silver tungsten will underperform even though its data sheet looks better.

Finally, check the process. Can the material be joined to the carrier with the available method? Can it be inspected? Can it be supplied at the volume and lead time the programme needs? Only then compare cost per operation.

• Low current, resistance-sensitive, high volume: silver nickel is usually the better fit.
• High current, frequent arcing, welding risk: silver tungsten or a tungsten-containing grade.
• Capacitive or lamp loads with high inrush: check welding resistance before choosing silver nickel.
• Tight space with limited force: silver nickel is easier to make work.
• Long life with a stable face: silver tungsten, if the force and heat path allow it.

Test before you commit

A material comparison on paper is a shortlist, not a decision. Build a test that uses the real load, the real closing force and the real opening speed. Measure contact resistance cold and after a run, record the temperature rise, and inspect the face at intervals rather than only at the end.

For welding, use a test that reproduces the inrush. A resistive load will not show the welding risk that a capacitive or lamp load will. For erosion, run enough operations to see the trend, not just the first few thousand. Photograph the face at each inspection so the change can be reviewed later.

Keep the material batch and the joining parameters with the results. A change in powder supplier, sintering cycle or infiltration temperature can shift performance, and without the batch record the test cannot be repeated.