# Alloy 908 UNS N09908: Properties and Applications
## Introduction to Alloy 908 UNS N09908
Alloy 908, also known as UNS N09908, is a nickel-iron-based superalloy designed for cryogenic applications. This material is particularly known for its excellent mechanical properties at extremely low temperatures, making it a preferred choice for various specialized industries.
## Chemical Composition
Keyword: Alloy 908 UNS N09908
The unique properties of Alloy 908 stem from its carefully balanced chemical composition:
– Nickel (Ni): 48-50%
– Iron (Fe): 38-42%
– Cobalt (Co): 4.5-5.5%
– Niobium (Nb): 2.7-3.3%
– Titanium (Ti): 1.3-1.7%
– Aluminum (Al): 0.75-1.25%
This composition provides the alloy with its characteristic combination of strength, toughness, and low thermal expansion.
## Mechanical Properties
Alloy 908 exhibits remarkable mechanical properties, especially in cryogenic environments:
– Tensile Strength: 1,240 MPa (180 ksi) at room temperature
– Yield Strength: 1,000 MPa (145 ksi) at room temperature
– Elongation: 12% minimum
– Excellent fracture toughness at cryogenic temperatures
– Low thermal expansion coefficient
## Physical Properties
The physical characteristics of Alloy 908 include:
– Density: 8.19 g/cm³ (0.296 lb/in³)
– Melting Range: 1,370-1,425°C (2,500-2,600°F)
– Thermal Conductivity: 11.7 W/m·K at 20°C
– Electrical Resistivity: 85 μΩ·cm at 20°C
## Key Advantages
Alloy 908 offers several distinct advantages:
– Exceptional strength-to-weight ratio
– Outstanding cryogenic performance
– Good weldability compared to other superalloys
– Excellent resistance to hydrogen embrittlement
– Low thermal expansion characteristics
## Primary Applications
Due to its unique properties, Alloy 908 finds applications in several critical areas:
### Aerospace Industry
– Cryogenic fuel tanks for spacecraft
– Components for liquid hydrogen and oxygen systems
– Structural elements in satellites
### Energy Sector
– Superconducting magnet systems
– Components for fusion reactors
– Cryogenic storage vessels
### Research and Development
– Particle accelerator components
– Cryogenic research equipment
– High-field magnet systems
## Fabrication and Processing
Working with Alloy 908 requires special considerations:
– Machining: Requires rigid setups and sharp tools due to work hardening
– Welding: Can be welded using conventional methods, but requires post-weld heat treatment
– Heat Treatment: Typically solution annealed at 980°C (1,800°F) followed by aging
– Forming: Can be cold worked but requires intermediate annealing for severe deformation
## Comparison with Other Superalloys
Compared to similar materials, Alloy 908 offers:
– Better cryogenic performance than Inconel 718
– Lower thermal expansion than 304 stainless steel
– Superior strength at low temperatures compared to titanium alloys
– Better resistance to hydrogen embrittlement than many high-strength steels
## Future Prospects
As cryogenic technology advances, the demand for Alloy 908 is expected to grow in:
– Next-generation space exploration vehicles
– Advanced magnetic confinement fusion reactors
– Quantum computing infrastructure
– High-energy physics research facilities
Alloy 908 UNS N09908 represents a critical material solution for extreme low-temperature applications where conventional materials fail. Its unique combination of properties ensures its continued importance in cutting-edge technological applications that push the boundaries of material performance.
