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Nimonic 75: Properties and Applications in High-Temperature Environments
Nimonic 75 is a nickel-chromium alloy known for its exceptional strength and resistance to oxidation at elevated temperatures. Developed in the mid-20th century, this superalloy has become a cornerstone in industries where high-temperature performance is critical. Its unique combination of mechanical properties and corrosion resistance makes it a preferred material for demanding applications.
Chemical Composition and Key Properties
The chemical composition of Nimonic 75 plays a crucial role in its performance characteristics. The alloy primarily consists of:
- Nickel (Ni): 72-77% (provides the base matrix and corrosion resistance)
- Chromium (Cr): 18-21% (enhances oxidation resistance)
- Iron (Fe): 5% maximum (typically present as an impurity)
- Titanium (Ti): 0.2-0.6% (contributes to precipitation hardening)
- Carbon (C): 0.10% maximum (affects mechanical properties)
These elements combine to give Nimonic 75 its distinctive properties:
- Excellent creep resistance at temperatures up to 815°C (1500°F)
- Outstanding oxidation resistance in continuous service up to 925°C (1700°F)
- Good mechanical strength maintained at high temperatures
- Superior resistance to thermal fatigue
- Good fabricability and weldability compared to other superalloys
Mechanical Properties at Elevated Temperatures
One of the most remarkable aspects of Nimonic 75 is its ability to maintain mechanical integrity under extreme heat. At room temperature, the alloy typically exhibits:
- Tensile strength: 690-860 MPa (100-125 ksi)
- Yield strength: 275-550 MPa (40-80 ksi)
- Elongation: 30-45%
As temperatures increase, Nimonic 75 demonstrates superior performance compared to conventional alloys:
| Temperature (°C) | Tensile Strength (MPa) | 0.2% Proof Stress (MPa) |
|---|---|---|
| 20 | 760 | 345 |
| 600 | 620 | 275 |
| 700 | 480 | 205 |
| 800 | 275 | 140 |
Heat Treatment and Microstructure
Keyword: nimonic 75
The performance of Nimonic 75 can be optimized through proper heat treatment. The standard treatment involves:
- Solution treatment at 1080-1120°C (1975-2050°F) followed by rapid cooling
- Aging at 700-750°C (1290-1380°F) for 16 hours to precipitate strengthening phases
This treatment results in a microstructure consisting of:
- A gamma (γ) nickel matrix with chromium in solid solution
- Fine gamma prime (γ’) precipitates (Ni3(Al,Ti)) that provide precipitation strengthening
- Chromium carbides at grain boundaries for improved creep resistance