Superalloys and EDM

Their strength is their weakness

One valuable characteristic that separates electrical discharge drilling machining from more conventional machining methods is its ability to drill through materials that are very resilient with great efficiency. Altough many of these materials are natural elements such as tantalum and niobium, most are elemental mixtures called superalloys. These superalloys generally share a face-centred cubic crystal structure, a structure that results in a great strength through its many chemical bonds. The following materials are used by many of the customers in a wide variety of applications.

  • Hastelloy – Used in the pressure vessels of nuclear and chemical reactors, Hastelloy is a nickel-based alloy that resists corrosion.
  • Invar – A material originally developed by Swiss physicist Charles Èdouard Guillaume, Invar is a nickel and iron composite with an anomalously low coefficient of thermal expansion. Because of its dimensional stability, it is commonly found in precision instruments.
  • Kovar – Kovar is an alloy designed to match the coefficient of thermal expansion of glass. This allows it to be used as a seal with glass, lending it to use in glass instruments containing a vacuum, such as light bulbs and vacuum tubes.
  • Niobium – The characteristics of niobium lend it to use in many different alloys, with varying applications. It can be added to steels to improve its general strength, used in superalloys to increase hardness, and in superconducting magnets.
  • Tantalum – An element with extremely similar characteristics to niobium, tantalum’s applications overlap quite a bit with those of niobium. Like niobium, it is used in corrosion-resistant materials, while its high melting point lend it to use in vacuum furnaces.
  • Stellite – A corrosion-resistant and very hard material, Stellite is used for machine parts and tooling. They are also used for valve components in internal combustion engines.

The same properties that make superalloys so valuable in extreme engineering projects make them very difficult to work with, and many of these materials would in fact be useless if not for machining methods like electrical discharge machining. Electrical discharge machining operates on principles that sidestep the physical properties of superalloys that make them so robust and does not drill by physical contact. In facilitating the manipulation of superalloys, EDM-drilling gives engineers the freedom to use whatever material suits the application, even materials that resist conventional machining.