Invar
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Image:Invar-Graph-CTE-composition.png Invar, also called FeNi36, 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 (CTE). It was invented in 1896 by Charles Edouard Guillaume, who later received the Nobel Prize in Physics in 1920.
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,[1] valves in motors, etc.) However, it has a propensity to creep.
Although Invar is today a widely used material in many industries and applications, this is a particular trademark of a French company named Imphy Alloys: this company originates from the Acieries D'Imphy (a small city near Nevers, France) where the alloy was initially industrialised after its invention. The generic reference for Invar(R) is FeNi36.
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, ...
- FeNiCo alloys - named Kovar or Dilver P - that have the same expansion behaviour as glass, and because of that are used for optical parts in a wide range of temperatures and applications, such as satellites.
External links
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