Invar
Invar, also called FeNi, is an alloy of iron (64%) and nickel
(36%) with some carbon and chromium. This alloy is known worldwide
for its unique properties of controlled coefficient of thermal
expansion
Due to its low coefficient of thermal expansion at room
temperature (about 10-6 K-1 in length;
some formulations have negative CTE) it is used in precision
instruments (clocks, physics laboratory devices, seismic creep
gauges, shadow-mask frames, valves in motors, etc.) However, it has
a propensity to creep.
Although Invar is today a widely used material in many
industries and applications,
There are variations of the original Invar material that have
slightly different coefficient of thermal expansion such as: FeNi42
which matches the CTE of silicon and therefore is widely used as
lead frame material for electronic components, integrated circuits,
etc.
FeNiCo alloys - named Kovar or Dilver P- that have the same expansion
behavior as glass, and because of that are used for optical parts
in a wide range of temperatures and applications, such as
satellites.
