Kovar (trademark of Carpenter Technology Corporation) is a nickel–cobalt ferrous alloy compositionally identical to Fernico 1, 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 Fe–Ni alloys with these particular thermal expansion properties. Note the related particular Fe–Ni alloy Invar which exhibits minimum thermal expansion.
Given in weight %
|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)||5.5|
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