When selecting materials for specialized applications, Invar and Kovar are two commonly used alloys, each with distinct properties. Understanding their differences is essential for choosing the right material for your project.

What is Invar?

Invar is a nickel-iron alloy containing 36% nickel. It is known for its exceptionally low thermal expansion, making it ideal for applications that require dimensional stability across varying temperatures. Additionally, Invar retains its toughness and strength even at cryogenic temperatures.

What is Kovar?

Kovar is a nickel-cobalt alloy specifically designed for compatibility with borosilicate glass and ceramics. It is widely used in sealed electrical components, metal-ceramic packages, and other precision applications. Kovar offers excellent machinability, allowing for the production of components with tight tolerances. It also exhibits strong resistance to chemical corrosion and thermal shock.

Key Differences Between Invar and Kovar

1. Color

• Invar: Silver-gray with a matte finish.
• Kovar: Also silver-gray but more lustrous due to its cobalt content.

2. Density

• Invar: Lower density at approximately 8.1 g/cm³.
• Kovar: Slightly higher density at 8.36 g/cm³.

3. Hardness

• Invar: Softer, with a hardness of around 160 HB.
• Kovar: Harder, with a hardness of approximately 210 HB.

4. Strength

• Invar: Lower tensile strength of around 500 MPa.
• Kovar: Higher tensile strength, reaching 700 MPa.

5. Melting Point

• Invar: 1425°C, slightly lower than Kovar.
• Kovar: 1430°C, offering a marginally higher melting point.

6. Thermal Conductivity & Expansion

• Invar: Moderate thermal conductivity and very low thermal expansion, making it ideal for precision instruments.
• Kovar: Low thermal conductivity but thermal expansion properties that match glass and ceramics, making it suitable for hermetic sealing.

7. Electrical Conductivity

• Invar: Low electrical conductivity due to its high nickel content.
• Kovar: Higher electrical conductivity, suitable for specialized electronic applications.

8. Corrosion Resistance

• Invar: Moderate resistance; requires protective coatings in harsh environments.
• Kovar: Better corrosion resistance due to its cobalt content.

9. Magnetic Properties

• Invar: Highly magnetic.
• Kovar: Magnetic, but with slightly lower magnetism than Invar.

10. Weldability

• Invar: Highly weldable but requires careful handling to prevent distortion.
• Kovar: Easily weldable with seamless performance.

11. Recyclability

• Invar: Highly recyclable and widely reused in industries focused on sustainability.
• Kovar: Also recyclable, though less commonly reused than Invar.

12. Cost

• Invar: More affordable due to its simpler composition.
• Kovar: More expensive because of its cobalt content.

Choosing Between Invar and Kovar

• For applications requiring low thermal expansion and stability: Invar is the ideal choice.
• For applications involving glass or ceramic seals and electrical components: Kovar is the better option.

By understanding these differences, manufacturers can make informed decisions about material selection, ensuring optimal performance and cost-effectiveness for their specific applications.