Alloy 718 vs. Inconel 718: A Comprehensive Comparison
In the world of high-performance alloys, Alloy 718 and Inconel 718 are often used interchangeably, leading to confusion about whether they are the same material or not. This article aims to clarify their relationship, explore their characteristics, and provide a comparative analysis of their performance and chemical compositions.
Understanding Alloy 718 and Inconel 718
Alloy 718 is a nickel-based superalloy renowned for its exceptional strength, corrosion resistance, and ability to withstand high temperatures. It was developed in the 1950s by Special Metals Corporation, making it one of the earliest superalloys designed for high-stress environments, including aerospace applications.
Inconel 718, on the other hand, is a trademarked name for the same alloy by the Special Metals Corporation. The term “Inconel” is a brand name that has become synonymous with certain nickel-chromium alloys noted for their high resistance to corrosion and oxidation.
Chemical Composition
The chemical composition of Alloy 718/Inconel 718 is crucial in defining its properties, particularly its strength and resistance to various forms of degradation. Below is a typical composition table for Alloy 718/Inconel 718:
| Element | Composition (%) |
|---|---|
| Nickel (Ni) | 50-55 |
| Chromium (Cr) | 17-21 |
| Iron (Fe) | 18.5 min (balance) |
| Niobium (Nb) | 4.75-5.50 |
| Molybdenum (Mo) | 2.80-3.30 |
| Titanium (Ti) | 0.65-1.15 |
| Aluminum (Al) | 0.20-0.80 |
| Cobalt (Co) | 1.00 max |
| Manganese (Mn) | 0.35 max |
| Silicon (Si) | 0.35 max |
| Copper (Cu) | 0.30 max |
Key Performance Characteristics
1. Strength and Toughness:
- Alloy 718/Inconel 718 exhibits excellent tensile and yield strengths, maintaining these properties across a broad temperature range. This makes it suitable for applications requiring high strength at both room and elevated temperatures.
2. Corrosion Resistance:
- The alloy demonstrates outstanding resistance to corrosion and oxidation, particularly in environments where sulfides and chlorides are present. This property is critical in aerospace and marine applications.
3. Heat Resistance:
- With a melting point of around 1300°C (2372°F), Alloy 718/Inconel 718 retains its strength and mechanical properties at high temperatures, making it suitable for use in turbines, engines, and other high-heat environments.
4. Fatigue Resistance:
- It has good fatigue resistance, which is essential for components subjected to cyclic loading, such as turbine blades and springs.
5. Weldability:
- Alloy 718/Inconel 718 is generally weldable using conventional techniques, although precautions must be taken to avoid the formation of brittle phases and maintain the alloy’s properties post-weld.
Applications
The versatility and robustness of Alloy 718/Inconel 718 make it indispensable in various industries:
- Aerospace: Gas turbine engines, rocket motors, and airframe components.
- Power Generation: Turbine blades, seals, and fasteners.
- Oil and Gas: Wellhead components, blowout preventers, and downhole tools.
- Automotive: Turbocharger turbines and exhaust systems.
- Marine: Propeller blades, shafts, and seawater applications.
Comparison with Other Materials
To understand where Alloy 718/Inconel 718 stands among similar materials, consider the following comparison:
| Material | Alloy 718/Inconel 718 | Alloy 625 | Alloy X-750 |
|---|---|---|---|
| Nickel (Ni) | 50-55 | 58 | 70.0 |
| Chromium (Cr) | 17-21 | 20-23 | 14.0-17.0 |
| Iron (Fe) | 18.5 min | 5.0 max | 5.0-9.0 |
| Molybdenum (Mo) | 2.80-3.30 | 8.0-10.0 | 1.0-2.75 |
| Titanium (Ti) | 0.65-1.15 | – | – |
| Aluminum (Al) | 0.20-0.80 | – | 0.40-1.0 |
| Niobium (Nb) | 4.75-5.50 | – | 0.70-1.20 |
| Tensile Strength (MPa) | 1000-1200 | 760-1100 | 1200-1400 |
| Yield Strength (MPa) | 800-1000 | 330-830 | 800-1000 |
| Density (g/cm³) | 8.2 | 8.4 | 8.2 |
| Applications | High-temp aerospace, | Chemical processing, | Springs, industrial |
| marine, power generation | marine, oil & gas | machinery |
Conclusion
In conclusion, while Alloy 718 and Inconel 718 are often used interchangeably, they refer to the same high-performance nickel-based superalloy developed by Special Metals Corporation. Its remarkable strength, corrosion resistance, and ability to withstand high temperatures make it a cornerstone material in demanding industries such as aerospace, oil and gas, and power generation. Understanding its composition and performance characteristics is essential for selecting the right material for specific applications where reliability and durability are paramount. Whether referred to as Alloy 718 or Inconel 718, this alloy continues to push the boundaries of what is possible in extreme environments.
By clarifying their similarities and differences, this article aims to provide a comprehensive guide to Alloy 718/Inconel 718, ensuring clarity for engineers, researchers, and enthusiasts alike who seek to harness the power of this exceptional material.