Invar is a metal
alloy invented by
Charles Edouard Guillaume that exhibits nearly zero
thermal expansion. That is, it grows/shrinks very little when subjected to moderate heating/cooling. This
property is very useful in
precision machinery. Invar is used
frequently in very
precise mechanical clocks, scientific instruments, color
CRT shadow masks, some
surveying tapes (now replaced by
laser rangefinding),
VHF/
UHF/
microwave duplexers and other
resonant cavities.
NASA used a rare
alloy of
Invar to make the
camera on the
spacecraft Cassini.
Invar should be treated nicely as dropping it will disturb the grain structure and possibly make it magnetic.
Invar is relativley simple alloy made of steel with about 36% nickel and tiny amounts of other elements. Invar 36 is a common grade and exhibits a very small coefficent of thermal expansion (1.6*10-6/K) but is a pain in the ass to machine. Another Invar alloy, FM (free machining) is much nicer to work with. It has more maganese and selenium as well as twice as much carbon as Invar 36 (which can lead to lower long-term stability). Super Invar has a much lower coefficent of thermal expansion (0.63*10^-6/K) but has some wack properties like spontaneously changing size and is still a son of a bitch to machine.