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Alloy 909 (UNS N19909) Overview and Applications

Introduction to Alloy 909

Alloy 909, also known by its UNS designation N19909, is a low-expansion, iron-nickel-cobalt superalloy designed for applications requiring exceptional dimensional stability over a wide temperature range. This alloy is particularly valued for its unique combination of thermal, mechanical, and magnetic properties.

Key Characteristics

Alloy 909 offers several distinctive properties that make it suitable for specialized applications:

• Low thermal expansion coefficient
• Excellent dimensional stability
• Good strength at elevated temperatures
• Controlled thermal expansion characteristics
• Resistance to oxidation and corrosion

Chemical Composition

The typical composition of Alloy 909 includes:

• Nickel (Ni): 38-42%
• Cobalt (Co): 13-17%
• Iron (Fe): Balance
• Small amounts of titanium, silicon, and other trace elements

Physical Properties

Some notable physical properties of Alloy 909 include:

• Density: 8.19 g/cm³
• Melting Range: 1425-1455°C (2600-2650°F)
• Thermal Expansion Coefficient: 5.1-7.6 μm/m·°C (20-400°C)

Mechanical Properties

Alloy 909 demonstrates excellent mechanical properties:

• Tensile Strength: 655 MPa (95 ksi) min
• Yield Strength: 345 MPa (50 ksi) min
• Elongation: 20% min

Primary Applications

Due to its unique properties, Alloy 909 finds use in various demanding applications:

• Aerospace components requiring dimensional stability
• Precision instruments and measurement devices
• Glass-to-metal seals
• Cryogenic applications
• Electronics packaging
• Laser components

Fabrication and Processing

Alloy 909 can be processed using standard techniques, though some considerations apply:

• Machinability similar to austenitic stainless steels
• Weldable using conventional methods
• Requires controlled heat treatment for optimal properties

Advantages Over Other Alloys

Compared to similar alloys, Alloy 909 offers:

• Better dimensional stability than standard Invar alloys
• Superior strength at elevated temperatures
• More consistent thermal expansion characteristics

Conclusion

Alloy 909 (UNS N19909) represents an excellent material choice for applications where dimensional stability, controlled thermal expansion, and good mechanical properties are critical. Its unique combination of properties makes it indispensable in aerospace, precision instrumentation, and other high-tech industries where performance under varying thermal conditions is paramount.</