Kovar Alloy

Kovar alloy is an iron-nickel-cobalt controlled expansion alloy for glass sealing, also known as Kovar Glass Sealing Alloy, 4J29 alloy, GB 4J29, ASTM F15, Nilo Alloy K, UNS K94610, 1.3981, FeNi29Co17, Pernifer 2918, NiCo29-18. The alloy has a linear expansion coefficient similar to that of borosilicate hard glass at 20-450°C, a higher Curie point（435 ℃）, and good low-temperature microstructure stability. The oxide film of the alloy is dense and can be well wetted by glass. It does not interact with mercury, and is suitable for use in instruments containing mercury discharge.

Main Standard

• AMS-I-23011
• MIL-I-23011 C

Magnetic properties

Kovar alloy is magnetic at all temperatures below the Curie point. Magnetic properties will depend upon heat treatment; the lower the hardness, the higher the permeability values and lower hysteresis loss

Main features

It has a linear expansion coefficient similar to that of hard glass in a certain temperature range

Thermal Expansion Curve

Main application:

The alloy is a typical Fe-Ni-Co hard glass sealing alloy commonly used in the electric vacuum industry and hard glass for matching and sealing, it is the main sealing structure material for electric vacuum devices. It has been used for a long time in the aviation factory with stable performance. It is mainly used for glass sealing of electric vacuum components such as High power delivery valves, transistor leads and heaters, and photographic flashes, launch tubes, oscillator tubes, ignition tubes, magnetrons, transistors, sealed plugs, relays, integrated circuit lead wires, chassis, shells, brackets, etc. In the application, the selected glass should be matched with the expansion coefficient of the alloy. Strictly test its low temperature tissue stability according to the use temperature. Appropriate heat treatment should be carried out during processing to ensure that the material has good deep drawing properties. When using forgings, their air tightness should be strictly checked.

Scope of supply

1. Sheet and foil, thickness 0.01 – 5.0mm, width 2000mm, hot rolled or cold rolled, annealed, pickled
2. Strip coil, Thickness: 0.01mm-5.0mm, width ≤ 650mm, commonly used are 100mm, 150mm, 200mm, 300mm, 350mm, cold rolled, annealed, pickled or bright annealed
3. Flat wire, strip, customized production for customers
4. Round plates and rings, thickness 0.01 – 5.0mm, φ100 – 2000mm, hot rolled or cold rolled, annealed, pickled or machined
5. Bar & tube, φ10 – 200mm, forged material, hot rolled material, cold drawn material, annealed state, pickled, machined or polished
6. Forging parts, irregularly shaped forgings are provided upon request
7. Wire, φ0.01 – 15.0mm, bright brushed, Hard, 1 / 4Hard, 1 / 2Hard, Soft, coiled, wrapped around a shaft or in roll form
8. Kovar spherical powder

International equivalent grade comparison table

Chemical composition(%)

Physical properties

Average Linear Expansion Coefficient

Magnetic Permeability

Kovar Alloy will be magnetic at all temperatures below the Curie Point. Magnetic Properties depend upon Heat Treatment. The softer the material, the higher the Permeability Values and lower Hysteresis Loss. Examples of Permeability are as below：

Flux Density: Magnetic, Electric or Radiant Flux per unit area normal to the direction of the flux.

Kovar powder (spherical powder)

Kovar Alloy Powder photo

Kovar powder micrograph