Controlled Expansion Alloys
Kovar, 45/46 Alloy, 4750 Alloy, 48 Alloy, 49 Alloy, 52 Alloy
Controlled expansion alloys are iron-nickel alloys or iron-nickel-cobalt alloys used for applications in which thermal size change of the metal must be considered in the design. Composition and crystal structure help to determine each alloy’s thermal expansion behavior. The alloy expansion rate is most commonly stated in terms of an average coefficient of thermal expansion. Controlled expansion alloys were developed to demonstrate a coefficient of thermal expansion within certain ranges.
Controlled expansion alloys fall into three categories: low thermal expansion, matching expansion and high thermal expansion. The most common controlled expansion alloys are:
Kovar: Kovar is most commonly used for high integrity glass and ceramic to metal seals, lids, lead frames and electronic package base in the military and defense, telecommunications and aerospace industries.
45/46 Alloy: With a relatively constant rate of thermal expansion to about 800°F (538°C), this low expansion alloy has been used mostly in electronic applications, especially for glass and ceramic seals as well as thermostats, and its thermal expansion is similar to some alumina ceramics.
47/50, 48, 49 Alloy: This soft, magnetic alloy consists of 49% nickel and is used where high initial permeability, maximum permeability, and low core loss is needed, widely used in the aircraft and aerospace industries.
52 Alloy: Consisting of 51% nickel, this nickel iron alloy is suitable for glass and ceramic sealing to metal. 52 Alloy is used predominantly in magnetic reed blade switches, lead wire for mercury switches and in semiconductor devices.