Following on our success with Invar 36, Signicast 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 thus “in-variant” to temperature, Kovar is designed to be “co-variant”. It was designed so that its CTE closely matched that of borosilicate glasses but it is a good match for some alumina ceramics as well.
Benefits and Applications of Kovar
Kovar’s thermal expansion rate is the key property that makes this super-alloy useful. Compared to other alloys, Kovar expands at a variable rate with increasing temperature with very little change in dimension. This makes Kovar a great 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 oxidizing treatment to the parts after they have been annealed. The oxide layer is intermediary, bonding both to the glass and to the alloy substrate on which it was formed. The hermetic seal creates a bond 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 among many others.
Physical and Mechanical Properties
By varying the amounts of the major alloying elements, the CTE behavior of these alloys can be tailored to match different ceramics and glasses.
Kovar’s typical physical and mechanical and physical properties are as follows:
- Density: .302 lb/in3roperties are as follows:
- Curie Temperature: 435 ºC
- Melting Point: 1450 ºC
- Specific Heat:
- .105 cal/gm/ ºC at 0 ºC
- .155 cal/gm/ ºC at 430 ºC
- Heat of Fusion: 64 cal/gm
- Thermal Conductivity: 17.3 W/m · K
- 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, Signicast is redefining how today’s manufacturers create, refine, and deliver products. Whatever your situation, our expert engineering staff is ready to listen. With 30 in-house engineers, we partner with you on every project to ensure your component is the highest quality possible. Contact our engineering team today to get the conversation started.