Materials
Kovar vs Invar: Which Low-Expansion Alloy Do You Need?
Both control expansion, but they answer different questions. Kovar is designed to seal to glass; Invar is designed to stay put in free space.
Side-by-side
Comparison
| Property | Kovar | Invar 36 |
|---|---|---|
| Coefficient of expansion | ~5.1 ppm/K | ~1.2 ppm/K |
| Designed to match | Borosilicate glass, ceramics | Optical benches, precision frames |
| Thermal expansion vs steel | Much lower | ~1/5 of steel |
| Magnetic | Ferromagnetic | Ferromagnetic |
| Typical use | Glass-to-metal seals, hermetic packages | Laser/optical mounts, metrology, satellite hardware |
Decision guide
How to decide
- Choose Kovar when the part must seal to glass or ceramic and stay hermetic across temperature cycles.
- Choose Invar 36 when a structure must hold its dimensions as the environment warms and no glass seal is involved.
- Both are ferromagnetic - if magnetic behaviour matters, neither is the neutral choice.
FAQ
Frequently asked questions
No. Kovar's expansion is matched to specific glasses and ceramics; Invar is chosen for open structures that must stay dimensionally stable. Substituting one for the other usually breaks the seal or the stability.
Both work-harden and conduct heat poorly, so both are demanding. Neither is a material to treat as ordinary steel.
Yes, both are ferromagnetic, which matters in sensors, magnetic shielding and instrumentation.
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