Kovar alloy spotlight

Following our success with Invar 36, CIREX is excited to offer Kovar, an iron-nickel-cobalt alloy, to our customers. Kovar is another alloy that exhibits the “Invar Effect.” The thermal expansion is low and linear below the Curie Point and much higher above the Curie Point. Whereas Invar is designed to have a very low coefficient of thermal expansion (CTE) and is therefore “invariant” to temperature, Kovar is designed to be “co-variant”. Its CTE therefore closely matches that of borosilicate glasses, but it is a good match for some alumina ceramics too.

Kovar alloy properties and benefits

Kovar’s thermal expansion rate makes this superalloy so useful. Compared to other alloys, Kovar expands at a variable rate with increasing temperature and with very little change in dimension. This makes Kovar an excellent fit for seals and glass-to-metal bonded assemblies with minimal locked-in pressure.

It is used in applications requiring a hermetic seal between the metal alloy and the glass or ceramic component. The metal to glass seal is created by performing an oxidising treatment on the annealed parts. The oxide layer is intermediary, bonding to both the glass and the alloy substrate on which it was formed. The hermetic seal creates a bond that is free of the trouble and failures caused by dirt, dust, moisture, fungus or lack of pressure at high altitudes. Applications for this alloy include X-ray tubes, microwave tubes, and light bulb ends.

Physical and Mechanical Properties

The CTE behaviour of these alloys can be tailored to match different ceramics and glasses by changing the amounts of the major alloying elements used.

Kovar’s typical physical and mechanical and physical properties are:

  • Density: .302 lb/in
  • Curie Temperature: 435 ºC
  • Melting Point: 1450 ºC
  • Heat of Fusion: 64 cal/gm
  • Thermal Conductivity: 17.3 W/m · K
  • Specific Heat:
    • 155 cal/gm/ ºC at 430 ºC
    • 105 cal/gm/ ºC at 0 ºC
  • Electrical Resistivity: 490 microhm/mm
  • Shear Modulus: 7.5 · 106
  • Modulus of Elasticity: 20 · 106
  • Ultimate Tensile Strength: 75,000 psi
  • Yield Strength: 50,000 psi
  • Elongation: 30%
  • Hardness (Rockwell B): 78

Investment Casting Manufacturer

With world-leading experts, rapid prototyping and delivery, and the most advanced investment casting facilities in the world, CIREX is redefining how today’s manufacturers create, refine and deliver products. Whatever your situation, our expert engineering staff are ready to listen. With 30 in-house engineers, we partner with you on every project to ensure your component has the highest quality possible. Contact our engineering team today to get the conversation started.