What Is Invar?

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In the world of materials science, certain alloys possess extraordinary properties that make them invaluable for specific applications. One such alloy is Invar, a unique iron-nickel alloy renowned for its remarkable thermal stability and low coefficient of thermal expansion. In this blog post, we will delve into the fascinating characteristics of Invar, its composition, applications, and the reasons behind its exceptional performance.

What Is Invar?

Invar is a trademarked name for an iron-nickel alloy known as Fe-Ni36 or 36% Nickel Steel. It was first developed in the early 20th century by Swiss scientist Charles Édouard Guillaume. The name “Invar” is derived from the word “invariable” due to its exceptional dimensional stability under varying temperature conditions.

Composition And Structure:

Invar primarily consists of 36% nickel and 64% iron. This precise composition gives Invar its unique properties. The addition of nickel significantly reduces the coefficient of thermal expansion, resulting in its exceptional dimensional stability. The crystal structure of Invar is face-centered cubic (FCC), which further contributes to its low thermal expansion.

Remarkable Properties Of Invar:

1. Low Coefficient of Thermal Expansion:

The most notable property of Invar is its incredibly low coefficient of thermal expansion. Invar exhibits minimal dimensional changes when subjected to temperature variations, making it ideal for applications requiring high precision and stability. This property is attributed to the balanced lattice expansion of iron and nickel in the alloy.

2. Thermal Stability:

Invar maintains its dimensional stability across a wide temperature range, typically from cryogenic temperatures up to around 200-300°C (392-572°F). This exceptional thermal stability makes it valuable in environments where temperature fluctuations occur, such as aerospace, scientific instruments, and precision engineering.

3. High Mechanical Strength:

Invar possesses good mechanical strength, allowing it to withstand external forces and stresses. It retains its strength even at low temperatures, making it suitable for applications in cryogenic environments.

4. Magnetic Properties:

Invar exhibits a unique combination of low coercivity and high magnetic permeability. This property makes it useful in applications where controlled magnetic properties are required, such as in magnetic shielding and precision instrumentation.

Applications Of Invar:

1. Precision Instruments:

Invar’s low thermal expansion and stability make it indispensable in precision instruments like scientific devices, optical equipment, and surveying instruments. It ensures accurate measurements and maintains calibration under varying temperature conditions.

2. Aerospace and Satellite Technology:

Invar’s exceptional thermal stability and low thermal expansion make it crucial in aerospace applications. It is used in the construction of satellites, aerospace instruments, and components that require dimensional stability and resistance to thermal cycling.

3. Clocks and Watches:

Invar’s stability and low thermal expansion make it a preferred material in the manufacturing of precision timekeeping devices. It helps maintain accurate timekeeping by minimizing the effects of temperature variations on the mechanical components.

4. Electrical and Electronic Applications:

Invar is used in electrical and electronic applications, including electric resistors, thermostats, and bimetallic strips. Its low thermal expansion allows for reliable performance and consistent electrical characteristics.


Invar, with its exceptional thermal stability, low coefficient of thermal expansion, and other remarkable properties, continues to play a significant role in various industries and applications. Its ability to maintain precise dimensions and resist thermal fluctuations makes it invaluable in fields that demand high precision and stability. As a testament to its scientific and engineering prowess, Invar has become a staple material in precision instruments, aerospace technology, and countless other areas where dimensional accuracy and stability are paramount.

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What Is Invar Used For?

Invar, alloy of iron that expands very little when heated; it contains 64 percent iron and 36 percent nickel. Invar was formerly used for absolute standards of length measurement and is now used for surveying tapes and in watches and various other temperature-sensitive devices.

How Is Invar Produced?

Invar alloy according to the present invention is formed by electroplating using a solution containing water, ferrous chloride, nickel sulfate, nickel chloride, hydrochloric acid, saccharin, sodium lauryl sulfate, calcium chloride as an electrolyte solution.

What Type Of Metal Is Invar?

nickel-iron alloy

Invar is generally a nickel-iron alloy. However, in this pure mix, the alloy is extremely hard to find. Not to mention that it can be difficult to machine. That is why you will generally find Invar alloys with additions of other materials that improve machinability and are easier to come by.

What Is The Meaning Of Invar Rod?

Invar® (UNS K93600) is a unique nickel-iron controlled expansion alloy. With a composition of 36% nominal nickel and the balance Iron, Invar Alloy has the lowest thermal expansion of any known alloy. Another key factor is that Invar exhibits a very low expansivity below its Curie Temperature.


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