Invar, also known generically as FeNi36 (64FeNi in the US), is a nickel steel alloy notable for its uniquely low coefficient of thermal expansion (CTE or α). It was invented in 1896 by Swiss scientist Charles Édouard Guillaume. He received the Nobel Prize in Physics in 1920 for this discovery, which shows the importance of this alloy in scientific instruments. "Invar" is a registered trademark of ArcelorMittal - Stainless & Nickel Alloys, formerl...
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Invar, also known generically as FeNi36 (64FeNi in the US), is a nickel steel alloy notable for its uniquely low coefficient of thermal expansion (CTE or α). It was invented in 1896 by Swiss scientist Charles Édouard Guillaume. He received the Nobel Prize in Physics in 1920 for this discovery, which shows the importance of this alloy in scientific instruments. "Invar" is a registered trademark of ArcelorMittal - Stainless & Nickel Alloys, formerly known as Imphy Alloys (US Trademark #63970), however FeNi36 is also manufactured by Japanese companies. Like other nickel/iron compositions, Invar is a solid solution; that is, it is a single-phase alloy — similar to a dilution of common table salt mixed into water. The name "Invar" comes from the word invariable, referring to its lack of expansion or contraction with temperature changes.
Common grades of Invar have an α (20–100 °C) of about 1.2 × 10 K (1.2 ppm/°C). However, extra-pure grades (
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