Iron-Nickel-Cobalt Low Expansion Alloy

Alloy K is an iron-nickel-cobalt alloy designed for precise and uniform thermal expansion chracteristics. The coefficient of thermal expansion of nickel and iron is more or less the same. However, adding nickel to iron can result in an alloy with a reduced coefficient of thermal expansion by an order of magnitude. These characteristics make them suitable for use in a myriad of applications, including medical, electronics, aerospace engineering, telecommunications and cryogenic components.

Iron-nickel alloys demonstrate a very low expansion rate at room temperature. These low thermal expansion alloys have been used in modern applications which require joining of a metal to glass or ceramics and in areas that demand same thermal expansion rates for materials to be joined in order to prevent associated problems within the joint area.

Alloy K (K94610/ASTM F15)

Alloy K, also known as Nilo K and Kovar, consists of 29% nickel and 17% cobalt. Its composition is strictly controlled within narrow limits to ascertain accurate and universal thermal expansion and mechanical properties. This facilitates the alloy provide high integrity ceramic-to-metal and glass-to- metal seals in applications demanding thermal shock resistance and reliability.

Conditioning the alloy utilizing thermal degassing / decarburising in a moist hydrogen atmosphere is recommended so as to attain optimum conditions for subsequent sealing operations. The conditioned material is then subjected to a controlled oxidation heat treatment to form a tightly adherent surface oxide film of optimum thickness and nature.

Properties of Alloy K

The following are the typical physical properties of Alloy K:

Coefficient of thermal expansion: 4.6-5.2 at 30-400 °C; 5.1-5.5 at 30-450 °C
Density: 8.25 g/cm3
Melting point: 1450 °C
Curie point: 425 °C
Thermal conductivity: 17.0 W/m°C
Specific heat: 0.50 J/g.°C
Young's modulus (MPa): 139,000

Applications of Alloy K

Alloy K is often utilized with both alumina type ceramic materials and the harder Pyrex or borosilicate glasses in the production of hermetic seals. It is widely used in the manufacture of diodes and transistors for lids and closures in many different hybrid electronic circuit packages as well as in the production of microwave tubes.

This information has been sourced, reviewed and adapted from materials provided by Columbia Metals.

For more information on this source, please visit Columbia Metals.

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