# Alloy 908 UNS N09908: Properties and Applications
## Introduction to Alloy 908
Alloy 908, also known as UNS N09908, is a nickel-iron-based superalloy designed for cryogenic applications. This material exhibits excellent mechanical properties at extremely low temperatures while maintaining good corrosion resistance and weldability.
## Chemical Composition
The chemical composition of Alloy 908 plays a crucial role in its performance characteristics:
– Nickel (Ni): 48-50%
– Iron (Fe): Balance
– Cobalt (Co): 4.0-5.0%
– Niobium (Nb): 2.7-3.3%
– Titanium (Ti): 1.3-1.7%
– Aluminum (Al): 0.75-1.25%
– Carbon (C): ≤0.03%
– Manganese (Mn): ≤0.50%
– Silicon (Si): ≤0.50%
– Phosphorus (P): ≤0.015%
– Sulfur (S): ≤0.015%
## Mechanical Properties
Alloy 908 demonstrates remarkable mechanical properties across a wide temperature range:
### Room Temperature Properties
– Tensile Strength: 965-1170 MPa (140-170 ksi)
– Yield Strength: 690-860 MPa (100-125 ksi)
– Elongation: 15-25%
– Modulus of Elasticity: 190 GPa (27.5×10⁶ psi)
### Cryogenic Temperature Properties (4K)
– Tensile Strength: 1650-1930 MPa (240-280 ksi)
– Yield Strength: 1240-1520 MPa (180-220 ksi)
– Elongation: 20-30%
– Fracture Toughness: Excellent
## Physical Properties
The physical characteristics of Alloy 908 include:
– Density: 8.19 g/cm³ (0.296 lb/in³)
– Melting Range: 1350-1400°C (2460-2550°F)
– Thermal Expansion Coefficient: 10.8×10⁻⁶/°C (6.0×10⁻⁶/°F) at 20-100°C
– Thermal Conductivity: 11.7 W/m·K (81 BTU·in/hr·ft²·°F) at 20°C
– Electrical Resistivity: 0.85 μΩ·m at 20°C
## Key Features and Advantages
Alloy 908 offers several unique advantages:
– Exceptional strength and toughness at cryogenic temperatures
– Low thermal expansion coefficient
– Good weldability compared to other superalloys
– Excellent resistance to hydrogen embrittlement
– Maintains mechanical properties after prolonged exposure to cryogenic temperatures
– Good fatigue resistance
## Heat Treatment
Proper heat treatment is essential for optimizing Alloy 908’s properties:
Keyword: Alloy 908 UNS N09908
– Solution Annealing: Typically performed at 980-1010°C (1800-1850°F) followed by rapid cooling
– Aging: Carried out at 720-760°C (1325-1400°F) for 8 hours, followed by air cooling
## Applications
Alloy 908 finds its primary use in cryogenic applications, particularly in:
### Superconducting Magnet Systems
– Structural components for large superconducting magnets
– Support structures in fusion reactors
– Magnetic confinement devices
### Aerospace Industry
– Cryogenic fuel storage and handling systems
– Components for space exploration vehicles
– Liquid hydrogen containment systems
### Energy Sector
– Components for hydrogen energy systems
– Cryogenic pumps and valves
– Superconducting power transmission systems
### Research Facilities
– Particle accelerator components
– Nuclear magnetic resonance (NMR) equipment
– Cryogenic research apparatus
## Fabrication and Machining
Working with Alloy 908 requires special
