# Alloy 903 UNS N19903: Properties and Applications

## Introduction to Alloy 903 UNS N19903

Alloy 903, also known by its UNS designation N19903, is a high-performance nickel-iron-cobalt superalloy. This material is renowned for its unique combination of properties, making it suitable for demanding applications in various industries. Its controlled thermal expansion characteristics and excellent mechanical properties have positioned it as a material of choice for specialized engineering applications.

## Chemical Composition

The chemical composition of Alloy 903 plays a crucial role in its performance characteristics. The primary elements include:

– Nickel (Ni): 38-41%
– Iron (Fe): Balance
– Cobalt (Co): 14-17%
– Niobium (Nb): 4.5-5.5%
– Titanium (Ti): 1.3-1.7%
– Aluminum (Al): 0.6-1.0%

This carefully balanced composition contributes to the alloy’s unique properties, including its low thermal expansion characteristics and high strength at elevated temperatures.

## Physical Properties

Alloy 903 exhibits several notable physical properties:

– Density: 8.25 g/cm³
– Melting Range: 1315-1365°C (2400-2490°F)
– Thermal Expansion Coefficient: Low and controllable
– Electrical Resistivity: 0.85 μΩ·m at 20°C
– Magnetic Permeability: Typically low

These properties make Alloy 903 particularly valuable in applications where dimensional stability across temperature ranges is critical.

## Mechanical Properties

The mechanical properties of Alloy 903 UNS N19903 are impressive:

– Tensile Strength: 1100-1300 MPa (160-190 ksi)
– Yield Strength: 900-1100 MPa (130-160 ksi)

– Elongation: 10-15%
– Hardness: 35-40 HRC
– Fatigue Strength: Excellent

These characteristics are maintained over a wide temperature range, making the alloy suitable for both cryogenic and elevated temperature applications.

## Thermal Properties

Alloy 903’s thermal properties are among its most distinctive features:

– Thermal Conductivity: 11.7 W/m·K at 20°C
– Specific Heat Capacity: 460 J/kg·K at 20°C
– Thermal Expansion: Controlled and predictable
– Maximum Service Temperature: Approximately 650°C (1200°F)

The alloy’s low and predictable thermal expansion makes it particularly valuable in applications requiring precise dimensional control.

## Corrosion Resistance

While not primarily designed as a corrosion-resistant alloy, Alloy 903 demonstrates:

– Good resistance to oxidation at elevated temperatures
– Moderate resistance to various corrosive environments
– Better performance than many steels in certain conditions

For applications requiring superior corrosion resistance, protective coatings or different alloy selections may be necessary.

## Fabrication and Processing

Alloy 903 can be processed using standard techniques:

– Machining: Possible but challenging due to high strength
– Welding: Can be welded using appropriate techniques
– Heat Treatment: Typically solution treated and aged
– Forming: Can be formed using standard methods

Special consideration must be given to the alloy’s work hardening characteristics during fabrication.

## Applications of Alloy 903 UNS N19903

The unique properties of Alloy 903 make it suitable for various demanding applications:

### Aerospace Industry

– Jet engine components
– Turbine seals
– High-precision structural components

### Power Generation

– Gas turbine components
– Steam turbine parts
– Power transmission systems

### Precision Engineering

– Optical mounting systems
– Laser components
– Scientific instruments

### Other Applications

– Cryogenic equipment
– High-performance fasteners
– Specialized tooling

## Advantages of Alloy 903

The key advantages of Alloy 903 include:

– Excellent strength-to-weight