Why Are Powder Metallurgy Materials Used in Contact Point Manufacturing?
2026-10-29
A relay manufacturer returns a batch of Contact Points after field failures. The contacts have welded together in service, and the normally open circuit stayed closed after the coil was de-energized. The failure analysis shows that the contact material was a cast silver alloy with a coarse grain structure and a segregation band of low melting point phase. The cast structure could not resist the arc energy, and the contact surfaces fused. The manufacturer now specifies a powder metallurgy material with a fine dispersion of refractory particles. This change is not cosmetic. It changes the way the material behaves under the arc. This guide explains why powder metallurgy materials are used in Contact Points manufacturing.
1. Why Does a Contact Point Need a Material That Cannot Be Made by Simple Melting and Casting?
A Contact Points must conduct current with low resistance, resist arc erosion when the circuit opens, resist welding when the circuit closes, and maintain a stable contact resistance over millions of operations. These requirements pull in opposite directions. Silver has excellent conductivity but poor arc resistance and a low melting point. Tungsten has excellent arc resistance but high contact resistance. A material that combines both must have a fine, uniform distribution of the refractory phase in the silver matrix. Melting and casting cannot produce this structure because the two phases are mutually insoluble and separate during solidification. The refractory particles sink or float, and the resulting casting has a coarse and segregated structure. In our factory, we manufacture Contact Points by powder metallurgy to avoid this limitation. DONGGUAN INT METAL TECH CO.,LTD. has been manufacturing electrical contact materials for over 12 years.
The casting route also limits the composition range. Many high performance contact materials, such as silver tungsten and silver tungsten carbide, cannot be produced by melting at all because the tungsten does not dissolve in the silver. Powder metallurgy allows the composition to be set by weight ratio rather than by solubility.
2. How Does Powder Metallurgy Combine Metals That Cannot Be Alloyed by Melting?
Powder metallurgy builds the material from particles instead of from a melt. The process has four steps. The first is powder production. The silver powder and the refractory powder are produced separately, with controlled particle size. The second is mixing. The two powders are blended in the required ratio, with a lubricant to aid compaction. The third is compaction. The blended powder is pressed in a die at high pressure to form a green compact. The fourth is sintering. The compact is heated below the melting point of silver, and the silver particles bond to each other while the refractory particles remain dispersed. The table below compares the melting route and the powder metallurgy route for common contact material systems.
| Material system | Melting and casting | Powder metallurgy |
| Silver nickel | Partial solubility; segregation possible | Uniform dispersion; composition flexible |
| Silver tungsten | Not possible (mutually insoluble) | Standard production route |
| Silver tungsten carbide | Not possible | Standard production route |
| Silver tin oxide | Difficult; oxide agglomeration | Uniform oxide dispersion |
| Silver cadmium oxide | Possible but segregation | Uniform dispersion; being phased out |
In our factory, we control the particle size distribution of the silver powder and the refractory powder to achieve a uniform dispersion after sintering. A narrow particle size distribution produces a more uniform microstructure and a more consistent arc erosion behavior. DONGGUAN INT METAL TECH CO.,LTD. provides the particle size analysis with each production lot.
3. What Happens to the Microstructure and Arc Erosion Resistance During Sintering?
Sintering is the step that converts the pressed powder into a solid material. During sintering, the silver particles bond to each other by diffusion, and the compact densifies. The refractory particles remain in place and pin the grain boundaries, which prevents the silver grains from growing. The result is a fine grain structure with a uniform dispersion of the refractory phase. This structure resists arc erosion because the refractory particles increase the effective melting point of the surface and distribute the arc energy over a larger area. The table below shows the effect of sintering temperature and time on density, hardness, conductivity, and arc erosion resistance.
| Sintering condition | Density (% theoretical) | Hardness (HV) | Conductivity (% IACS) | Relative arc erosion resistance |
| Low temperature, short time | 88 – 92% | 60 – 75 | 85 – 90% | Baseline |
| Optimal temperature and time | 95 – 98% | 85 – 105 | 80 – 88% | 1.3 – 1.5x baseline |
| High temperature, long time | 98 – 99% | 75 – 90 | 82 – 90% | 1.0 – 1.2x baseline |
| Over-sintered | > 99% | 65 – 80 | 85 – 92% | 0.8 – 0.9x baseline |
Contact engineer's note: The optimal sintering condition is not the one that gives the highest density. Over-sintering closes the pores but also coarsens the microstructure and reduces the arc erosion resistance. The best combination is a density of 95 to 98 percent of theoretical, a hardness of 85 to 105 HV, and a conductivity of 80 to 88 percent IACS. In our factory, we verify the density by the Archimedes method, the hardness by Vickers testing, and the conductivity by the eddy current method. DONGGUAN INT METAL TECH CO.,LTD. provides the test report with each batch.
4. Why Does Powder Metallurgy Allow Graded and Layered Contact Structures?
A Contact Points often benefits from a graded structure. The surface layer should have high arc resistance, and the base layer should have high conductivity to carry the current and to conduct the heat away from the arc. Powder metallurgy allows the two layers to be pressed together in the die and sintered in one cycle. The interface between the layers is a metallurgical bond, not a braze or a weld. The bond is uniform and has no flux residue. The graded structure reduces the amount of expensive refractory material and improves the heat dissipation. In our factory, we press the surface layer and the base layer in a single die and sinter the compact in one cycle. We control the layer thickness and the interface quality by the compaction pressure and the sintering profile. DONGGUAN INT METAL TECH CO.,LTD. produces two-layer and three-layer Contact Points for high current switching applications.
We also inspect the interface by metallography. The interface should show a continuous bond with no voids or cracks. The bond strength is verified by a shear test on a sample from each lot.
5. How Should Engineers Specify and Verify Powder Metallurgy Contact Points?
The specification should include the material system, the composition ratio, the density, the hardness, the conductivity, the arc resistance requirement, the layer structure, and the dimensional tolerance. The verification should include four checks. The first is the density measurement by the Archimedes method. The second is the conductivity measurement by the eddy current method. The third is the metallographic examination of the microstructure and the layer interface. The fourth is the arc erosion test under the specified electrical load. In our factory, we perform all four checks on a sample basis for each production lot and provide the test report with the shipment. DONGGUAN INT METAL TECH CO.,LTD. also offers a design review service to help the customer select the material system and the layer structure for the specific switching duty.
We recommend that the designer specify the contact resistance limit after the arc erosion test, not only the initial contact resistance. A contact that has a low initial resistance but a high resistance after 10,000 operations will cause overheating in service. The specification should include the contact resistance at the end of the life test.
Frequently Asked Questions About Powder Metallurgy Contact Points
Summary for Electrical Contact Engineers
Powder metallurgy materials are used in Contact Points manufacturing because they allow the combination of metals that cannot be alloyed by melting, they produce a fine and uniform microstructure that resists arc erosion, and they enable graded and layered structures that optimize the surface and the base separately. The key parameters are the material system, the composition ratio, the sintering condition, the density, and the layer structure. The verification should include density, hardness, conductivity, metallography, and arc erosion testing. DONGGUAN INT METAL TECH CO.,LTD. has been manufacturing electrical contact materials for over 12 years and provides full material selection and verification support for our customers.
