Kovar Alloy UNS K94610: Properties and Applications

July 21, 2025 / By

# 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 known for its unique thermal expansion properties. This specialized material was developed to match the thermal expansion characteristics of certain types of glass and ceramics, making it invaluable in various technical applications.

## Chemical Composition

The chemical composition of Kovar alloy UNS K94610 typically includes:

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

## Key Properties

### Thermal Expansion

Kovar’s most notable property is its low coefficient of thermal expansion (CTE), which closely matches that of borosilicate glass (about 5.3 × 10-6/°C between 30-200°C). This characteristic minimizes thermal stress when the alloy is sealed to glass or ceramic components.

### Mechanical Properties

– Tensile strength: 517 MPa (75 ksi)
– Yield strength: 345 MPa (50 ksi)
– Elongation: 30%
– Hardness: Rockwell B 90

### Other Properties

– Density: 8.36 g/cm³
– Curie temperature: ~435°C
– Electrical resistivity: 49 μΩ·cm
– Thermal conductivity: 17.3 W/m·K

## Applications of Kovar Alloy

### Electronics and Telecommunications

Kovar is widely used in electronic packaging where glass-to-metal seals are required. Common applications include:

– Transistor and diode packages
– Microwave tubes
– X-ray tubes
– Cathode ray tubes
– Hermetic seals for electronic components

### Aerospace Industry

The alloy finds applications in aerospace for:

– Satellite components
– Spacecraft instrumentation
– Sensor housings
– High-reliability electronic systems

### Scientific Instruments

Kovar is used in various scientific instruments that require precise thermal matching:

– Vacuum systems

– Laser components
– Optical devices
– Laboratory equipment

## Fabrication and Processing

### Machining

Kovar can be machined using standard techniques, though it work-hardens rapidly. Recommended practices include:

– Using sharp tools with positive rake angles
– Maintaining adequate coolant flow
– Employing slower speeds than for mild steel

### Joining Methods

Common joining techniques include:

– Glass-to-metal sealing
– Brazing (using silver-based alloys)
– Welding (TIG or resistance welding preferred)

### Heat Treatment

Kovar typically undergoes a hydrogen anneal at 1000°C (1832°F) to improve its sealing characteristics and remove surface oxides.

## Advantages of Kovar Alloy

– Excellent thermal expansion match with certain glasses and ceramics
– Good mechanical strength
– Reliable hermetic sealing capability
– Corrosion resistance in many environments
– Stable performance over wide temperature ranges

## Limitations and Considerations

While Kovar offers many benefits, designers should consider:

– Higher cost compared to standard steels
– Limited availability in some forms
– Specialized processing requirements
– Potential for magnetic properties at certain temperatures

## Conclusion

Kovar alloy UNS K94610 remains an essential material in applications requiring precise thermal expansion matching with glass and ceramics. Its unique properties continue to make it indispensable in electronics, aerospace, and scientific instrumentation where reliable performance under thermal cycling is critical.