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Difference Between Kovar and Invar 36
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Difference Between Kovar and Invar 36
Kovar and Invar 36 are both nickel-iron alloys, but they have distinct compositions and properties that make them suitable for different applications.
1. Composition
| Alloy | Nickel (Ni) | Iron (Fe) | Cobalt (Co) | Other Elements |
|---|---|---|---|---|
| Kovar | 29% | Balance | 17% | Small amounts of Silicon (Si), Manganese (Mn), and Carbon (C) |
| Invar 36 | 36% | Balance | None | Small amounts of Silicon (Si) and Carbon (C) |
2. Key Properties
| Property | Kovar | Invar 36 |
|---|---|---|
| Coefficient of Thermal Expansion (CTE) | Matches borosilicate glass & ceramics (4.6-5.2 × 10⁻⁶ /°C) | Extremely low expansion (1.2 × 10⁻⁶ /°C from 20–100°C) |
| Magnetic Properties | Ferromagnetic | Ferromagnetic |
| Electrical Resistivity | ~0.48 µΩ·m | ~0.78 µΩ·m |
| Density | ~8.3 g/cm³ | ~8.1 g/cm³ |
| Melting Point | ~1450°C | ~1430°C |
| Strength & Hardness | Stronger & harder | Softer, more ductile |
3. Applications
🔹 Kovar:
Used in glass-to-metal seals due to its thermal expansion matching borosilicate glass and ceramics.
Found in electronic packages, vacuum tubes, and aerospace components.
Used in hermetic seals for electrical components.
🔹 Invar 36:
Known for ultra-low thermal expansion, making it ideal for precision instruments.
Used in optical devices, measuring instruments, and aerospace applications where dimensional stability is critical.
Applied in cryogenic systems due to its minimal size change at low temperatures.
Summary
Kovar is best for glass-to-metal seals and electronic enclosures due to its matched expansion properties.
Invar 36 is best for applications requiring minimal expansion, such as precision instruments and aerospace components.
