Iron-Nickel Low Expansion Alloy

Iron-nickel alloys are low thermal expansion alloys with a very low expansion rate at room temperature. These materials have found use 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.

The coefficient of thermal expansion of nickel and iron is more or less the same. Nevertheless, 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.

Alloy 36 (UNS K93601/ASTM F1684)

Alloy 36 is popular under several trade names, including Nilo 36 and Invar. The 36% nickel-iron alloy demonstrates a near zero rate of thermal expansion, which is roughly one tenth the expansion rate of carbon steels at a temperature range of -100 °C to 200 °C. Besides exhibiting a very low coefficient of linear thermal expansion over a broad range of temperatures of up to 200 °C, the alloy retains superior toughness and strength at cryogenic temperatures. This characteristic makes it ideal for many different low expansion or low temperature applications.

Properties of Alloy 36

The following are the typical physical properties of Alloy 36:

Coefficient of thermal expansion at 30-150 °C: 1.2-2.7
Density: 8.13 g/cm3
Melting point: 1450 °C
Curie point: 230 °C
Thermal conductivity: 10.5 W/m°C
Specific heat: 0.51 J/g.°C
Young's modulus (MPa): 140,000

Applications of Alloy 36

The low expansion characteristics of Alloy 36 make it suitable for applications that demand very minimal dimensional changes under temperature variations, such as radio and electronic devices; structural members in precision equipment such as cryogenic instrumentation, thermostats, measuring devices and lasers; and tooling for aerospace composites.

Alloy 36 has also found use in applications where it is used in combination with a high expansion material to make mechanical movement with respect to temperature changes, such as thermo-mechanical control and switchgear devices.

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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