Invar: discovery history, properties, and applications

The history of science and technology is rich in many significant discoveries, among which creating invar — an iron-nickel alloy — holds a special place. This material has a unique physical property — a practically zero coefficient of thermal expansion.

Creating invar was an important achievement in physics and materials science, opening new prospects in technology and production of precision instruments. The alloy remains relevant and in demand today, playing a key role in modern technologies and scientific research.

History of the discovery of invar

Charles Édouard Guillaume (1861–1938) was a well-known French physicist and metrologist. At the end of the 19th century he worked on creating a length standard independent of temperature. A length standard was needed for the development of science and technology and for measurement accuracy in industry and trade.

Guillaume conducted a series of experiments with various materials and found that an alloy of nickel and iron has a unique property — its temperature coefficient of linear expansion (TCLE) is very small and practically independent of temperature. This material was named invar. In 1920 Charles Guillaume was awarded the Nobel Prize in Physics for discovering invar, from which it became possible to manufacture precision instruments and devices.

Features of invar properties

Invar is a material that mainly consists of nickel (about 36% by mass) and iron (about 64%). The material’s melting temperature is +1425°C; density is 8,130 kg/m³.

The main physical properties of invar are:

• a very low temperature expansion coefficient — about 1.2×10⁻⁶°C⁻¹;
• high strength — in the work-hardened condition strip tensile strength is 930 MPa per GOST 14080-78.

The effect of vanishing thermal expansion occurs through compensation of TCLE by magnetostriction. That is, when the material is magnetized and demagnetized its linear dimensions and volume change, compensating thermal expansion.

Applications of invar

Thanks to its unique properties invar is widely used in various areas of industry and science:

• Production of precision instruments and tools. Length standards, geodetic instruments, thermometers, and other measuring tools are made from invar.
• Watchmaking. Invar is used in producing clock mechanisms.
• Medicine. The alloy is used to make implants and prostheses because invar does not cause rejection by the body and is not subject to corrosion.
• Space technology. Invar properties do not change under vacuum and low temperatures.
• Microelectronics. Chip substrates, laser installation surfaces, and waveguides are made from invar.

The alloy has elevated strength and elasticity, making it possible to manufacture complex structures and mechanisms from it. In addition, invar can be used to produce parts of any size and shape, including single pieces.

Alloys with specified TCLE produced by PZPS

PZPS produces not only invar (36N) but also other alloys with a specified temperature coefficient of linear expansion, including 29NK and 42N. We also develop new materials and production technologies according to customer technical requirements. For cooperation and purchasing precision alloy strip of the required thickness and width, call the listed phone number or leave requests on the website. Our staff will contact you and answer your questions in detail.

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