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1) "Invar" -- As to invar in·var
Pronunciation: 'in-"vär
Function: noun
Usage: often capitalized
Etymology: from Invar, a trademark
: an iron-nickel alloy that expands little on heating Pronunciation Symbols
Invar, also called FeNi, is an alloy of iron (64%) and nickel (36%) with some carbon and chromium. This alloy is known for its unique properties of controlled coefficient of thermal expansion (CTE). It was invented in 1896 by a Swiss 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 thermal expansion, NTE) it is used in precision instruments (clocks, physics laboratory devices, seismic creep gauges, shadow-mask frames,[1] valves in motors, antimagnetic watches, 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 Aciéries d’Imphy (a small city near Nevers, France) where the alloy was initially industrialised after its invention. The generic reference for Invar® 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, etc.
- 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.
Physicists consider true ideal Invar to be the pure bi-metallic alloy with stoichiometry Fe65Ni35 that has the face centered cubic crystal structure, since this laboratory alloy has all the essential properties of the commercial varieties. The Invar problem of physics has been to discover the microscopic mechanism that gives Invar its exceptional thermal properties. It was established early on that Invar behaviour is directly related to and dependent upon the alloy's ferromagnetism however the exact mechanism has been the subject of much research and debate, inc..."
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