Kovar® alloys

Kovar® alloy is an iron-nickel-cobalt alloy. Kovar® has been used for making hermetic seals with ceramic materials and glass. Kovar® has been used in power tube, microwave tubes, diodes and transistors.


Kovar (Nilo®, Alloy K) / 1.3981 / UNS K94610
NILO alloy K (UNS K94610/W. Nr. 1.3981), a nickel-iron-cobalt alloy containing approximately 29% nickel and 17% cobalt. Its thermal expansion characteristics match those of borosilicate glasses and alumina type ceramics. It is manufactured to a close chemistry range, yielding repeatable properties which make it eminently suitable for glass-to-metal seals in mass production applications, or where reliability is of paramount importance.

Available Forms for Kovar®

  • Wire
  • Bar
  • Sheet
  • Plate
  • Tube
  • Forgings
  • Welding Rod

Kovar Properties and Appearance

Chemical Comparison

Element Content
Carbon (Maximum) 0.02%
Silicon 0.20 %
Cobalt 17.00 %
Manganese 0.30 %
Nickel 29.00 %
Iron Balance

Physical Properties

Properties Imperial
Density 0.3020 lb/in³

Electrical Properties

Properties Imperial
Electrical Resistivity 70.0 °F 294.0 ohm-cir-mil/ft

Thermal Properties

Properties Imperial
Curie Temperature 815°F
Thermal Conductivity 120.0 BTU-in/hr/ft2/°F
Melting Range 2,642 °F

Kovar alloy is magnetic at all temperatures below the Curie point. Magnetic properties depends upon heat treatment; the lower the hardness, the higher the permeability values and lower hysteresis loss. Kovar alloy is manufactured to meet the requirements of ASTM Specification F-15.


UNS K94610

Werkstoff Nr 1.3981

DIN 17745


AMS 7726 Wire

AMS 7727 Bars and Forgings

AMS 7728 Sheet, Strip and Plate

MIL-I-23011 class 1

AFNOR NF A54-301

S.E.W 385



Kovar® Applications

As direct Kovar material suppliers, Magellan Metals distributes high-grade Kovar alloy products for a wide range of industries where dimensional changes due to temperature variation must be minimized, some of the applications where UNS K94610 is utilized include:

  • Hermetic seals
  • Power tubes
  • Microwave tubes
  • Diodes
  • Transistors
  • X-ray tubes