Kovar Alloy UNS K94610: Properties and Applications

# Kovar Alloy UNS K94610: Properties and Applications

## Introduction to Kovar Alloy UNS K94610

Kovar alloy, designated as UNS K94610, is a nickel-cobalt ferrous alloy specifically designed to match the thermal expansion characteristics of borosilicate glass. This unique property makes it an essential material in applications where a reliable glass-to-metal seal is required.

## Chemical Composition

The typical chemical composition of Kovar alloy includes:

– Iron (Fe): ~54%
– Nickel (Ni): ~29%
– Cobalt (Co): ~17%
– Trace elements: Manganese, Silicon, and Carbon

## Physical Properties

Kovar alloy exhibits several notable physical properties:

– Density: 8.36 g/cm³
– Melting Point: 1450°C (2642°F)
– Thermal Expansion Coefficient: Matches borosilicate glass (5.1 x 10⁻⁶/°C from 30°C to 200°C)
– Electrical Resistivity: 49 μΩ·cm at 20°C

## Mechanical Properties

The mechanical properties of Kovar alloy make it suitable for demanding applications:

– Tensile Strength: 517 MPa (75 ksi)
– Yield Strength: 345 MPa (50 ksi)
– Elongation: 30% in 50 mm
– Hardness: 82 HRB

## Thermal Properties

Kovar’s thermal properties are particularly important for its primary applications:

– Thermal Conductivity: 17.3 W/m·K at 20°C
– Specific Heat Capacity: 0.46 J/g·°C at 20°C
– Curie Temperature: ~435°C (815°F)

## Applications of Kovar Alloy

Due to its unique properties, Kovar alloy finds applications in various industries:

### Electronics and Telecommunications

– Hermetic seals in electronic packages
– Microwave tubes
– X-ray tubes
– Transistor and diode packages

### Aerospace and Defense

– Satellite components
– Radar systems
– Guidance system housings

### Scientific Instruments

– Laboratory equipment
– Vacuum systems
– Cryogenic applications

## Fabrication and Processing

Kovar alloy can be processed using standard metalworking techniques:

– Machining: Can be machined using standard tools, though it work-hardens
– Welding: Can be welded using TIG or resistance welding methods
– Heat Treatment: Typically annealed at 800-850°C (1472-1562°F)
– Glass Sealing: Requires special surface preparation for optimal bonding

## Advantages of Kovar Alloy

The primary advantages of Kovar alloy include:

– Excellent thermal expansion match with borosilicate glass
– Good mechanical strength
– Corrosion resistance
– Reliable hermetic sealing capability
– Good thermal conductivity

## Limitations and Considerations

While Kovar alloy offers many benefits, there are some limitations to consider:

– Higher cost compared to standard steels
– Limited availability in some forms
– Requires careful handling to prevent contamination before glass sealing
– Not suitable for high-temperature applications above its Curie point

## Conclusion

Kovar alloy UNS K94610 remains a critical material in applications requiring reliable glass-to-metal seals, particularly in the electronics and telecommunications industries. Its unique thermal expansion properties, combined with good mechanical characteristics, make it irreplaceable for many specialized applications. As technology advances, Kovar continues to play a vital role in enabling sophisticated electronic and scientific devices.