Kovar

From Wikipedia, the free encyclopedia
Jump to: navigation, search
For other uses, see Kovar (disambiguation).

Kovar (trademark of CRS Holdings, inc., Delaware[1]) is a nickelcobalt 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.

Typical composition[edit]

Given in weight %

Fe Ni Co C Si Mn
balance 29% 17% < 0.01% 0.2% 0.3%

Properties[edit]

Property sintered HIPed
Density / g cm3 8.0 8.35
Hardness / HV1 160 150
Youngs Modulus / GPa 138 138
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
(25–300 °C) 5.1
(25–400 °C) 4.9
(25–450 °C) 5.3
(25–500 °C) 6.2

References[edit]

  1. ^ USPTO United States Patent and Trademark Office (1993). "Trademark Assignment Abstract". Retrieved 18 June 2014. 

External links[edit]