Kovar Alloy Supply
Kovar is an iron-nickel-cobalt alloy, using 29% nickel. Kovar is a light gray, controlled expansion alloy with a dull or lustrous finish. Kovar has an extremely low coefficient of thermal expansion, that is very close to hard glass such as Pyrex and therefore perfect for the application of glass to metal hermetic seals. Chemically, it bonds to glass with oxides of nickel and cobalt. Cobalt makes the oxide layer easier to melt and dissolve in molten glass. Kovar is one of the most popular controlled expansion alloys as it is not porous.
Kovar Properties and Appearance
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.
High quality controls are applied to the manufacture of Kovar ® to ensure precise uniform thermal expansion properties. Kovar ® is vacuum melted so its chemical composition is controlled within limits to ensure precision hence why Kovar® is useful in hybrid electronic circuit packages.
Chemical Comparison
| Element | Nominal, % | Max % |
| Fe (Iron) | Balance | Balance |
| Ni (Nickel) | 29 | 29 |
| Co (Cobalt) | 17 | 17 |
| Mn (Manganese) | 0.45 | 0.5 |
| Si (Silicon) | 0.1 | 0.2 |
| C (Carbon) | 0.015 | 0.02 |
| Al (Aluminum) | 0.05 | 0.1 |
| Mg (Magnesium) | 0.05 | 0.1 |
| Zr (Zirconium) | 0.05 | 0.1 |
| Ti (Titanium) | 0.05 | 0.1 |
Physical Properties
| Properties | Imperial |
| Density | 0.3020 lb/in³ |
Thermal Properties
| Property | Value |
| Curie Temperature | 435°C |
| Melting Point | 1450°C |
| Temperature Range, °C | Average Linear Coefficient of Expansion |
| 30-200°C | 5.5 x 10^-6 cm/cm/˚C |
| 30-300°C | 5.1 x 10^-6 cm/cm/˚C |
| 30-400°C | 4.9 to 5.2 x 10^-6 cm/cm/˚C |
| 30-450°C | 5.1 to 5.5 x 10^-6 cm/cm/˚C |
| 30-500°C | 6.2 x 10^-6 cm/cm/˚C |
| 30-600°C | 7.9 x 10^-6 cm/cm/˚C |
| 30-700°C | 9.3 x 10^-6 cm/cm/˚C |
| 30-800°C | 10.4 x 10^-6 cm/cm/˚C |
| 30-900°C | 11.5 x 10^-6 cm/cm/˚C
|
Specific Heat
| – 0°C | 0.105 cal/gm/°C |
| 430°C | 0.155 cal/gm/°C |
| Heat of Fusion | 64 cal/gm |
| Transformation Temperature | Below -78.5°C
|
Thermal Conductivity
| 30°C | 0.0395 ± 0.001 cal/cm²/cm/ºC/sec |
| 100°C | 0.042 cal/cm²/cm/ºC/sec |
| 200°C | 0.045 cal/cm²/cm/ºC/sec |
| 300°C | 0.0485 cal/cm²/cm/ºC/sec |
| 400°C | 0.053 cal/cm²/cm/ºC/sec |
| 500°C | 0.0585 cal/cm²/cm/ºC/sec |
Applications
Kovar is used generally for industries where temperature change variations need to be minimized, hence why Kovar is used in x-ray tubes and microwave tubes where there are large variations in temperature. Kovar is popular for hermetic seals and used for making metal to glass or metal to ceramic seals. Kovar is also used in the medical, scientific, and research communities as well as in transformers, diodes, conductors, and transducers for its low coefficient of thermal expansion.
Examples of Kovar applications are:
- Light bulbs
- X-ray tubes
- Microwaves
- Diodes
- Transistors
Find out more about Low Expansion Alloys.
Kovar is a registered trademark of CRS Holdings LTD., Delaware, USA.
Formats supplied:
Vulcan Metal Group supplies Kovar® in block, rod, bar, strip, sheet, plate, wire, cube, crucibles and ingots. Custom machined and finished parts supplied to print.
Please contact us for more information on how Vulcan Metal Group can help you.
Address
Vulcan Metal Group LLC
23888 Madison Street
Torrance, CA 90505
United States
Phone / Fax
Phone: +1 310.882.6841
Fax: +1 310.893.0579
Cage Code
8FCY8
Quality Policy: Vulcan Metal Group, LLC. supplies mission critical, special purpose materials, and products at a competitive price. The company’s quality system is registered to ISO 9001 and AS9100 and follows its principles for the governance of the business. An active continual improvement program and compliance with all applicable OSHA, federal, and state regulations is maintained.