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Invar – A Legend in Metals

The History & Uses of Invar

The low expansion alloy known as Invar has been around for some time. In fact, 1996 marked the centennial of its discovery.

This alloy has been so important to scientific advancement that it earned the Nobel Prize in 1920 for its inventor, Charles-Edouard Guillaume, the first and only scientist in history to be so honoured for a metallurgical achievement.

Invar has developed into a family of low expansion, nickel-iron alloys including Free-Cut Invar “36” alloy, a variation of the original material with improved machinability. Both grades contain 36% nickel, key to achieving a low coefficient of expansion, and both continue as the most commonly used alloys in the group.

On Paper the downsides for Free-Cut Invar “36” alloy is negligible. Its coefficient of thermal expansion is slightly higher than that of the basic alloy, which is not enough to make a difference in part performance. Minimal loss in both transverse toughness and corrosion resistance. It may be necessary to clean and passivate the free-cut alloy to remove selenides from the surface. However, a good case can be made for the free-cut alloy because it machines without a hassle and often boosts production.

However due to the improvements in the quality of Invar production, advancements made in machining technology and capabilities Free Machining Invar is becoming less readily available in the common market place. Whilst Free Machining invar can still offer a slight production improvement, this is highly offset by the rising cost and availability of this grade.

These two alloys, along with the other Invar grades, have been used in a wide variety of both common-place and high technology applications. Commercial uses have proliferated over the years in fields as diverse as semiconductors, television, information technology, aerospace, and cryogenic transport. Invar has been used in a host of applications. Early uses include light bulbs and electronic vacuum tubes for radios; bimetals in ther-mostats for temperature control; lead-in seals of fluorescent lights; measuring devices for testing gages and machine parts; military and electronics applications where expansion control is critical; bimetals for circuit breakers, motor controls, TV temperature compensating springs, appliances and heaters, aerospace and automotive controls, heating and air conditioning, as well as many others.

With ever-increasing vigor, this 102 year old alloy continues to expand in usage, with newer applications like more sophisticated thermostatic controls, containers used to transport cryogenic liquid natural gas in tankers, shadow masks in high-definition television tubes, structural components in precision laser and optical measuring systems, wave guide tubes, microscopes, supports for giant mirrors in telescopes and scientific instruments requiring mounted lenses, composite molds used in building new generation aircraft, and in a range of scientific applications such as orbiting satellites, lasers, and ring-laser gyroscopes.

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