Kovar
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2008-04-22T14:59:59Z
Chowbok
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clean up, Replaced: ® → , typos fixed: Km → km using [[Project:AutoWikiBrowser|AWB]]
'''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<sup>-6</sup> /K between 30 and 200°C, to ~10×10<sup>-6</sup> /K at 800°C) in order to allow direct mechanical connections over a range of temperatures. It finds application in [[electroplate]]d conductors entering glass envelopes of electronic parts such as [[vacuum tubes]] (valves), X-ray and Microwave tubes and some [[lightbulb]]s.
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.
== Typical Composition ==
given in weight %
{| class="wikitable"
|-
! [[Fe]]
! [[Nickel|Ni]]
! [[Cobalt|Co]]
! [[Carbon|C]]
! [[Silicon|Si]]
! [[Manganese|Mn]]
|-
| balance
| 29%
| 17%
| <0.01%
| 0.2 %
| 0.3 %
|-
|}
== Properties ==
{| class="wikitable"
|-
! Property
! [[Sintering|sintered]]
! [[hot isostatic pressing|HIP]]ed
|-
| [[Density]] / g cm<sup>3</sup>
| 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
| colspan="2" align="center"| 17
|-
|[[Curie point|Curie Temperature]] / °C
| colspan="2" align="center"| 435
|-
|[[electrical resistivity]] Ω mm<sup>2</sup> / m
| colspan="2" align="center"| 0.49
|-
|[[specific heat]] J/gK
| colspan="2" align="center"| 0.46
|-
|[[thermal expansion coefficient]]/10<sup>-6</sup> K<sup>-1</sup> (25 – 200°C)
| colspan="2" align="center"| 5.2
|-
| align="right"| (25 – 300°C) ||colspan="2" align="center"| 5.1
|-
| align="right"| (25 – 400°C) ||colspan="2" align="center"| 4.9
|-
| align="right"| (25 – 450°C) ||colspan="2" align="center"| 5.3
|-
| align="right"| (25 – 500°C) ||colspan="2" align="center"| 6.2
|-
|}
==External links==
*[http://www.espimetals.com/tech/kovar.pdf Kovar specification sheet]
[[Category:Ferrous alloys]]
{{alloy-stub}}
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[[ja:コバール]]
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[[uk:Ковар]]