Kovar is an iron-nickel-cobalt alloy with a composition of approximately 29% nickel, 17% cobalt, and the balance iron. It is designed to have a coefficient of thermal expansion similar to that of borosilicate glass, making it ideal for glass-to-metal seals in electronic and scientific devices. It is commonly used in applications such as vacuum tubes, X-ray tubes, and other devices requiring a tight mechanical joint between metal and glass.

Alloy 42, on the other hand, is a nickel-iron alloy with a composition of about 42% nickel and the balance iron. It exhibits low and constant thermal expansion up to 300°C, making it suitable for applications where minimal thermal expansion is crucial. It is often used in metal-to-glass or metal-to-ceramic seals, electronic components, and semiconductor packages.

comparison

 

Kovar

 

Alloy 42

 

composition

 

thermal expansion

 Matches the thermal expansion of borosilicate glass

Approximately 5.0×10−6/°C5.0×10−6/°C, which is low compared to many metals

 Low and constant thermal expansion up to 300°C ranging from 4.0×10−6/°C4.0×10−6/°C to 7.4×10−6/°C7.4×10−6/°C depending on the temperature range

thermal conductivity

 ~ 14-16 W/m·K ~ 0.11 W/cm·°C

density

 ~8.2 g/cm³ 8.12 g/cm³

mechanical properties

 Good mechanical strength and ductility Tensile strength of 75 ksi, yield strength of 40 ksi, and elongation of 30%

example applications
  • Electronic Packaging: hermetic seals, lids, and lead frames for high-integrity glass and ceramics
  • Aerospace: for components requiring precise dimensional stability under thermal stress
  • Power Tubes and Microwave Tubes to ensure stable seals between metal and glass
  • Transistors and Diodes used in hybrid packages
  • Metal-to-Glass or Metal-to-Ceramic Seals for electronic components and semiconductor packages
  • Automotive and Industrial Lamps to ensure minimal thermal expansion
  • CRT Electron Guns -provide stability and precision
  • Lead Frames used in various electronic applications
  • Heat exchangers

summary

Both alloys are crucial in industries where thermal expansion and stability are critical. Typically, Kovar is used in glass-to-metal seals for electronic and scientific devices and Alloy 42 in metal-to-glass or metal-to-ceramic seals, electronic components, and semiconductor packages. Alloy 42’s low thermal expansion rate also makes it ideal for use in heat exchangers.

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