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Super Invar is a specialized nickel-iron alloy known for its ultra-low coefficient of thermal expansion, even lower than standard Invar 36. It typically contains around 31% nickel, 5% cobalt, and the balance iron. The addition of cobalt significantly reduces dimensional changes with temperature fluctuations, making Super Invar ideal for applications that demand extreme dimensional stability in environments with variable or cryogenic temperatures. This alloy is used in precision instruments, aerospace components, telescope structures, and laser systems, where even the slightest thermal expansion can lead to critical misalignments.
Chemical Composition of Super Invar
The precise alloying of Super Invar gives it its unique thermal and physical characteristics:
| Element | Content (%) |
|---|---|
| Nickel (Ni) | ~31 |
| Cobalt (Co) | ~5 |
| Iron (Fe) | Balance |
| Carbon (C) | ≤ 0.02 |
| Silicon (Si) | ≤ 0.3 |
| Manganese (Mn) | ≤ 0.5 |
Thermal Expansion Performance
The standout feature of Super Invar is its incredibly low coefficient of thermal expansion (CTE):
| Temperature Range | CTE (×10⁻⁶ /°C) |
|---|---|
| 20–100°C | ~0.3 |
| −100 to +100°C | < 0.5 |
These values are significantly lower than Invar 36’s ~1.2 × 10⁻⁶ /°C, making Super Invar the preferred choice for the most thermally stable applications.
Physical and Mechanical Properties
In addition to thermal stability, Super Invar offers reliable physical performance:
| Property | Value |
|---|---|
| Density | ~8.1 g/cm³ |
| Modulus of Elasticity | ~140 GPa |
| Hardness | ~135 HB |
| Tensile Strength | ~500 MPa |
| Yield Strength | ~275 MPa |
| Elongation | ~30% |
Applications of Super Invar
Due to its exceptional stability, Super Invar is used in highly specialized fields:
| Application Area | Examples |
|---|---|
| Metrology | Precision measuring devices, interferometers |
| Aerospace | Satellite frames, optical payload supports |
| Cryogenics | Low-temperature supports, transfer lines |
| Optics | Laser cavity frames, telescope mounting systems |
Machining and Handling Considerations
Super Invar is relatively soft and ductile, which helps in machining, but its tendency to work-harden should be managed carefully:
| Operation | Recommendation |
|---|---|
| Machining | Use sharp carbide tools, low speeds |
| Welding | Special low-expansion filler metals required |
| Heat Treatment | Annealing at ~875°C improves stability |
Super Invar vs Invar 36
While both alloys provide low thermal expansion, they differ in critical ways:
| Property | Invar 36 | Super Invar |
|---|---|---|
| Nickel Content | 36% | 31% |
| Cobalt Content | 0% | 5% |
| CTE (20–100°C) | ~1.2 ×10⁻⁶ /°C | ~0.3 ×10⁻⁶ /°C |
| Cost | Moderate | Higher |
| Magnetism | Magnetic | Magnetic |
Related Questions
What is Super Invar used for?
Super Invar is used in applications that require extreme dimensional stability such as optical instruments, aerospace structures, and cryogenic engineering.
What makes Super Invar different from Invar 36?
Super Invar contains about 5% cobalt, which gives it a much lower coefficient of thermal expansion than Invar 36, making it more suitable for precision applications.
Is Super Invar magnetic?
Yes, Super Invar is magnetic at room temperature, although its magnetic properties can be affected slightly by alloying with cobalt.