What is Nickel-Iron Alloys?
It is mainly an alloy composed of two elements: iron (Fe) and nickel (Ni).
- Invar
Also known as constant steel, Invar steel, or Invar alloy, was discovered in 1896 by Swiss physicist Charles Édouard Guillaume. He found a nickel-iron alloy with a thermal expansion coefficient close to zero, which earned him the Nobel Prize in Physics in 1920.
The name “Invar” derives from the word “Invariant,” meaning unchanged, directly highlighting the material’s unique property. Compared to other metallic materials, Invar exhibits an exceptionally low thermal expansion coefficient, allowing it to maintain excellent stability in environments with large temperature variations.
Even today, Invar is widely used in fields such as instrumentation, measurement, engineering, technology, and research.
The Invar series includes:
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- Invar 36
Also known as Alloy 36 or Invar steel, it is primarily composed of 36% nickel (Ni) and 64% iron (Fe).
This alloy is characterized by its extremely low thermal expansion coefficient, making it widely used in applications requiring dimensional stability and high precision.
Thermal Expansion Coefficient (CTE): 0.722 µin/in-°F (93.0°C).
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- Invar 32-5
Also known as Super Invar, it is primarily composed of 32% nickel (Ni) and 68% iron (Fe).
Starting at 20°C, Super Invar exhibits a thermal expansion coefficient at room temperature that is significantly lower about half that of Invar 36.
Additionally, Invar 32-52 contains 5.5% chromium (Cr) in its composition, which provides enhanced corrosion resistance compared to alloys without this additive.
Thermal Expansion Coefficient (CTE): 0.350 µin/in-°F (-55~95.0°C).
- Kovar
Also known as sealing alloy, Kovar is primarily composed of 29% nickel (Ni), 54% iron (Fe), and 17% cobalt (Co).
Most metal materials, due to their thermal expansion coefficient, cannot bond or seal with materials like glass because of thermal expansion and contraction. However, the advent of Kovar has resolved these challenges in applications like vacuum systems for technology, semiconductors, and electronic devices.
Kovar’s thermal expansion rate closely matches that of hard glass (borosilicate glass), ceramics, and quartz, making it suitable for situations requiring the integration and sealing of metals with hard and brittle materials.
Thermal Expansion Coefficient (CTE): 2.83~3.06 µin/in-°F (20~450°C).
Related properties of Nickel-Iron Alloy
The main characteristic is its extremely low thermal expansion coefficient (CTE), and due to this, the following properties are also derived:
1. Dimensional Accuracy and Stability:
Due to the advantage of a low thermal expansion coefficient, the impact of temperature changes is minimal. This makes it an excellent choice for applications requiring precise, high-accuracy machining or strict dimensional tolerance.
2. Not easily deformed
Under variations in high and low environmental temperatures, it effectively reduces deformation, warping, and cracking caused by temperature changes in the material.
3. Lower Magnetism:
Because the composition includes iron, it exhibits slight magnetic properties. As the nickel content increases and the iron content decreases, the alloy’s magnetism is reduced.
4. Good Mechanical Properties:
The alloy maintains stable and excellent strength and toughness even under changes in ambient temperature.
5. Resistance to Rusting:
In dry environments at room temperature, it has a certain level of corrosion resistance. However, in high-humidity environments, there is still a risk of rust formation on the material’s surface. This can be improved and enhanced by surface treatments to strengthen its corrosion resistance.
Composition of various types of Nickel-Iron Alloy
| Model
Composition |
Invar 36 | Invar 32-5 | Kovar |
| Ni | 36 ％ | 32 ％ | 29 ％ |
| Fe | 63 ％ | 62 ％ | 54 ％ |
| Co | – | 5.5 ％ | 17 ％ |
| Mn | 0.35 ％ | 0.40 ％ | 0.3 ％ |
| Si | 0.20 ％ | 0.25 ％ | 0.2 ％ |
| C | 0.02 ％ | 0.02 ％ | 0.02 ％ |
Applications of Nickel-Iron Alloys
1. Invar 36
(1) Precision Components and Equipment Instruments:
Due to the material’s low thermal expansion coefficient, it is ideal for applications requiring high dimensional precision. It is commonly used in structural components, supports, and various precision parts in precision instruments and optical equipment. Some application examples are as follows:
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- Precision Instruments for Semiconductor Manufacturing
- Supporting Structure Components for Electron Microscopes
- Lens and Reflector Mounts
- Optical Lens Related Components
- Balance Wheel and Hairspring in Watches
- Shadow Mask for Displays (OLED)
- Instruments and Equipment Used in Ships
- Frames and Joints of Ship Hulls
- Power and Cooling Systems for Ships
- Other Hull Structures Prone to Thermal Stress at Low Temperatures
(2) Aerospace and Space Industry:
During the manufacturing, usage, and flight processes, there are significant changes in temperature and pressure. It is essential to ensure the stability, dimensional accuracy, and proper functioning of related parts and equipment during operation. INVAR 36 is frequently used in aerospace-related equipment, parts, and instruments. Some application examples are as follows:
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- Satellite and Spacecraft Structures and Components
- Molds for Aircraft Parts
- Navigation Systems
- Electronic Control Devices
(3) Medical and Chemical Industry:
Equipment or components in this field are exposed to the corrosion of chemicals, temperature fluctuations, and high pressures. Therefore, they need to possess certain corrosion resistance and strength. Some application examples are as follows:
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- Medical Devices
- Laboratory Equipment
- Particle Accelerators
- Chemical Reactors
- Magnetic Resonance Imaging (MRI) Components
- Liquefied Natural Gas (LNG) Transport, e.g., NO.96 type gas storage tank membrane enclosure system
2. Invar 32-5
(1) Laser and Optical Field:
With its extremely low thermal expansion coefficient, Invar can maintain stable dimensions in precision optical and laser instrument components, preventing errors in related components due to temperature changes. This ensures high-precision control and measurement of the instruments. Some application examples are as follows:
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- Frame
- Substrate
- Support Structures
- Telescope
- Laser Workbench
- Ring Laser Gyroscope
(2) Electronic Components:
Due to the material properties of INVAR 32-5, it is commonly used in products that need to withstand high frequencies, are sensitive to temperature changes, and require high precision. For example, it is used for the bonding of metals with low-expansion materials (such as glass or quartz), and it effectively controls errors caused by temperature fluctuations. This ensures the structural, performance, and stability reliability of instruments and equipment during operation. Some application examples are as follows:
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- Semiconductor Processing Equipment Components
- Waveguides
- Vacuum Tubes
- Microwave Filters
(3) Medical Field:
With its excellent dimensional stability, it ensures high accuracy of equipment under varying environmental conditions. In imaging devices and diagnostic instruments, it helps improve the clarity and precision of medical images, which is crucial for patient diagnosis. Some application examples are as follows:
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- Surgical Instruments
- Precision Diagnostic Instruments
- Magnetic Resonance Imaging (MRI) Components
(4) Equipment:
Due to its low thermal expansion coefficient, it is frequently used in high-precision measuring instruments and mechanical equipment. It effectively reduces accuracy errors caused by temperature fluctuations, ensuring the reliability of the equipment. Some application examples are as follows:
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- Gauge Blocks
- Length Standards Tools
- Positioning Devices
- Components in Temperature Measuring Equipment
3. Kovar
(1) Electronic Components:
As a metal, Kovar has a thermal expansion rate similar to that of low-expansion materials like glass or ceramics, making it highly suitable for use in electronic, telecommunications, and semiconductor processing equipment. It is commonly used in components, packaging, or vacuum processes, as well as in other applications requiring precise fittings. Some application examples are as follows:
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- Integrated Circuits
- Optical Fiber Components
- Vacuum Tubes
- Diodes
- Hybrid Packaging
- Transistors
- Microwave Tubes
- Connectors
- Bases
- Electron Guns
- High Voltage Feedthroughs
- Packaging for Voltage-Controlled Surface Acoustic Wave Oscillators
(2) Medical Equipment:
With excellent biocompatibility, mechanical properties, and corrosion resistance, Kovar ensures stability and reliability under temperature changes and prolonged use. Some application examples are as follows:
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- Ceramic Surgical Instruments
- Imaging Systems for Endoscopes (Glass or Sapphire)
- Implantable Devices
(3) Equipment Instruments:
With its low thermal expansion properties and excellent mechanical performance, Kovar ensures that equipment remains unaffected, stable, precise, and durable under varying temperature conditions. Some application examples are as follows:
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- Spectrometers
- Sensors
- Gas Chromatographs
- Circuit Boards in Radar Systems
For Invar Processing Needs/Issues, Please Contact Insta Voxel.
At InstaVoxel we provide professional machining services for INVAR 36, INVAR 32-5 and KOVAR. Whether it is customized single-piece processing or mass production, we can provide you with efficient and precise processing solutions. If you have any questions or special processing needs, please feel free to contact us. Insta Voxel has extensive processing technology and experience, and is ready to provide you with expert service and assistance to ensure that your project meets the highest standards of quality and accuracy.
