Invar, which is short for “invariable,” is an iron-nickel alloy first discovered in 1896 and distinguished for its extremely low coefficient of thermal expansion (CTE) at room temperature. The chemical composition responsible for this property is approximately 36% nickel and 64% iron (indicated by the x-ray fluorescent scanner shown above), though trace amounts of aluminum, carbon, chromium, cobalt, magnesium, manganese, phosphorus, silicon, sulfur, titanium, or zirconium may also be included in the alloy, depending on the manufacturer.
Invar’s low CTE makes it the ideal material for parts, components, and assemblies that require high dimensional stability across varying temperatures. Invar’s dimensional stability is similar to glass and ceramic materials, and it’s ideal for use in creating glass-to-metal and ceramic-to-metal sealing components as well as sealing components for semiconductors and microprocessors, high-precision molds for aerospace manufacturing, bimetal thermostats, liquified natural gas tanker components and piping, magnetic shielding, optical equipment such as lens mountings, and precision optical and laser measuring equipment.
Transforming Invar into some of these components, however, requires some machining expertise, experience, and caution. Invar produces stringy, gummy chips which can wrap around the tooling and disrupt the flow of coolant. To avoid these problems, use chip breakers, rigidly support the high-speed steel or sintered carbide tooling, and ensure good lubrication and cooling. For welding applications, use TIG or enhanced MIG welding procedures, with argon or an argon/helium mix for the shielding gas.