In terms of conductivity, metallic electrodes outperforms graphite. Some examples of metal electrodes are brass, copper, silver, tungsten, copper tungsten, silver tungsten, and tungsten carbide. Brass is one of the first material used for EDM electrode. It is easy to machine and cheaper compared to other materials. The problem with brass is its high wear rate. This means that the electrode require frequent replacements if an operator was to produce consistent quality.
The development of new EDM equipment that featured transistorized, pulse-type power supplies made copper the most preferred metallic electrode. The combination of copper and certain power supply settings allowed for low wear burning. The structural integrity of copper also made it possible to create very fine surface finishes without needing special polishing circuits. An issue with using copper as electrode material is that its malleability makes it much more difficult to machine and grind. A workaround for this issue is the addition of minimal amount of other metal to make copper harder and making it easier to machine.
A company in Sweden that offers various types of electrodes and other machining essentials like diamond tools have more detailed information about high-conductivity electrodes.