Kovar Spotlight

Following the success of Invar 36, Signicast expands its offerings with Kovar, an iron-nickel-cobalt alloy. Kovar, sharing the "Invar Effect" with its predecessor, boasts low and linear thermal expansion below the Curie Point, then expands significantly above it. While Invar prioritises a minimal coefficient of thermal expansion (CTE) for temperature stability, Kovar's "co-variant" nature ensures its CTE closely aligns with borosilicate glasses and certain alumina ceramics.

What are the 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 oxidising 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 behaviour 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.