Alloy 909 UNS N19909: Properties and Applications

# Alloy 909 UNS N19909: Properties and Applications

## Introduction to Alloy 909

Alloy 909, also known as UNS N19909, is a low-expansion, iron-nickel-cobalt superalloy designed for applications requiring controlled thermal expansion characteristics. This unique material offers excellent dimensional stability across a wide temperature range, making it particularly valuable in aerospace, electronics, and precision engineering applications.

## Chemical Composition

The chemical composition of Alloy 909 plays a crucial role in its performance characteristics:

– Nickel (Ni): 38-42%
– Cobalt (Co): 13-17%
– Iron (Fe): Balance
– Niobium (Nb): 4.5-5.5%
– Titanium (Ti): 1.3-1.8%
– Silicon (Si): ≤0.5%
– Manganese (Mn): ≤0.5%
– Aluminum (Al): ≤0.2%
– Carbon (C): ≤0.05%

## Physical Properties

Alloy 909 exhibits several notable physical properties:

– Density: 8.19 g/cm³
– Melting Range: 1425-1455°C (2600-2650°F)
– Thermal Expansion Coefficient: 5.0-7.5 × 10⁻⁶/°C (20-300°C)
– Electrical Resistivity: 85 μΩ·cm at 20°C
– Thermal Conductivity: 11.7 W/m·K at 20°C

## Mechanical Properties

The mechanical properties of Alloy 909 vary depending on heat treatment and processing:

– Tensile Strength: 850-1100 MPa (123-160 ksi)
– Yield Strength: 700-900 MPa (102-130 ksi)
– Elongation: 10-20%
– Hardness: 25-35 HRC
– Modulus of Elasticity: 148 GPa (21.5 × 10⁶ psi)

## Heat Treatment

Proper heat treatment is essential for optimizing Alloy 909’s properties:

– Solution Annealing: 980-1010°C (1800-1850°F) followed by rapid cooling
– Aging Treatment: 720-760°C (1330-1400°F) for 4-8 hours, air cool
– Stress Relieving: 540-650°C (1000-1200°F) for 1-2 hours

## Key Characteristics

Alloy 909 offers several distinctive characteristics:

– Low thermal expansion coefficient
– Excellent dimensional stability
– Good mechanical strength at elevated temperatures
– Resistance to thermal fatigue
– Compatibility with glass and ceramic sealing
– Good corrosion resistance in various environments

## Applications of Alloy 909

Due to its unique properties, Alloy 909 finds applications in numerous industries:

### Aerospace Applications

– Jet engine components
– Turbine seals
– Exhaust systems
– Structural components requiring thermal stability

### Electronics Industry

– Lead frames
– Glass-to-metal seals
– Thermocouple sheaths
– Precision instruments

### Industrial Applications

– Molds for glass manufacturing
– Measuring devices
– Laser components
– Optical systems

## Fabrication and Machining

Working with Alloy 909 requires special considerations:

– Machining: Similar to austenitic stainless steels but with higher tool wear
– Welding: Can be welded using TIG or resistance welding methods
– Forming: Can be cold worked but requires annealing between operations
– Grinding: Requires proper cooling to prevent work hardening

## Corrosion Resistance

Alloy 909 demonstrates good corrosion resistance in:

– Atmospheric conditions
– Fresh and salt water
– Alkaline solutions
– Mild acidic environments

However, it is not recommended for strongly oxidizing or reducing environments.

## Comparison with Other Low-Expansion