Kovar
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Kovar (trademark of Carpenter Technology Corporation) is a nickel-cobalt ferrous alloy designed to be compatible with the thermal expansion characteristics of borosilicate glass (~5×10-6 /K between 30 and 200°C, to ~10×10-6 /K at 800°C) in order to allow direct mechanical connections over a range of temperatures. It finds application in electroplated conductors entering glass envelopes of electronic parts such as vacuum tubes (valves), X-ray and Microwave tubes and some lightbulbs.
The name Kovar is often used as a general term for FeNi alloys with these particular thermal expansion properties. Note the related particular Fe-Ni alloy Invar which exhibits minimum thermal expansion.
[edit] Typical Composition
given in weight %
| Fe | Ni | Co | C | Si | Mn |
|---|---|---|---|---|---|
| balance | 29% | 17% | <0.01% | 0.2 % | 0.3 % |
[edit] Properties
| Property | sintered | HIPed |
|---|---|---|
| Density / g cm3 | 8.0 | 8.35 |
| Hardness / HV1 | 160 | 150 |
| Youngs Modulus / GPa | 159 | 159 |
| reduction of area at fracture / % | 30 | 30 |
| yield strength / MPa | 270 | 270 |
| thermal conductivity / W/Km | 17 | |
| Curie Temperature / °C | 435 | |
| electrical resistivity Ω mm2 / m | 0.49 | |
| specific heat J/gK | 0.46 | |
| thermal expansion coefficient/10-6 K-1 (25 – 200°C) | 5.2 | |
| (25 – 300°C) | 5.1 | |
| (25 – 400°C) | 4.9 | |
| (25 – 450°C) | 5.3 | |
| (25 – 500°C) | 6.2 | |
[edit] External links
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