You need high strength and performance at elevated temperatures for aerospace engines. Inconel 718 delivers this advantage, making up over 30% of the finished component mass in modern aircraft engines. If your priority is superior corrosion resistance and flexibility, Inconel 625 stands out. When you compare Inconel 718 vs. Inconel 625, focus on your application’s demands. This guide helps you select the right superalloy for your aerospace project.
Key Takeaways
- Inconel 718 is ideal for high strength applications, especially in parts that face heavy loads and temperatures up to 700°C.
- Inconel 625 excels in corrosion resistance and flexibility, making it suitable for components exposed to harsh chemicals and high temperatures.
- Consider the specific needs of your aerospace project, such as strength, temperature limits, and corrosion resistance, when choosing between the two alloys.
- Both alloys require specialized machining and welding techniques, but Inconel 625 is generally easier to weld than Inconel 718.
- Use a decision tree to guide your selection process, focusing on your most critical requirements to avoid costly mistakes.
Inconel 718 vs. Inconel 625 quick Comparison
Chemical Composition
When you compare nickel 625 vs 718 chemical composition, you see both alloys contain nickel and chromium as their main elements. However, each alloy includes different additional elements that affect their performance in aerospace applications.
| Alloy | Main Elements | Additional Elements |
|---|---|---|
| Inconel 718 | Nickel, Chromium | Iron, Molybdenum, Niobium, Columbium |
| Inconel 625 | Nickel, Chromium | Molybdenum, Niobium |
These differences in chemical makeup lead to unique material properties for each alloy. Inconel 718 includes more strengthening elements, which gives it higher strength. Inconel 625 focuses on elements that boost superior corrosion resistance.
Purity
You want to know the purity of these nickel alloys because impurities can affect their mechanical properties and corrosion resistance. Both inconel 718 and inconel 625 maintain very low levels of sulfur and phosphorus, which helps ensure consistent performance.
| Alloy | Typical Sulfur (%) | Typical Phosphorus (%) | Other Notable Impurities (%) |
|---|---|---|---|
| Inconel 625 | ≤ 0.015 | ≤ 0.015 | Si ≤ 0.50, Mn ≤ 0.50 |
| Inconel 718 | ≤ 0.015 | ≤ 0.015 | Si ≤ 0.35, Mn ≤ 0.35 |
You can rely on both alloys for high purity in aerospace manufacturing.
Key Properties
The mechanical properties of inco 718 & 625 set them apart for different aerospace needs. Here is a performance comparison of their main strengths:
| Properties | Inconel 625 | Inconel 718 |
|---|---|---|
| Tensile Strength | 790–910 MPa | 930–1530 MPa |
| Yield Strength | 320–450 MPa | 510–1330 MPa |
| Elongation at Break | 33–34% | 12–50% |
| Temperature Resistance | Up to 980°C | Up to 700°C |
| Corrosion Resistance | Superior | Good |
| Weldability | Excellent | Good |
| Cost | Higher | Moderate |
You see that inconel 718 offers high strength and is ideal for parts that need to handle heavy loads. Inconel 625 stands out for superior corrosion resistance and higher temperature limits. The difference between suitable temperature of uns n06625 and uns n07718 material is clear: you can use inconel 625 at higher temperatures, while inconel 718 is best for high strength up to 700°C.
Corrosion Resistance
Inconel 625 provides superior corrosion resistance, especially in harsh chemical environments. You benefit from its high chromium and molybdenum content, which protects against aggressive chemicals and saltwater. Inconel 718 offers good oxidation resistance but does not match the corrosion resistance of inconel 625.
Thermal Properties
The thermal properties of uns n06625 & n07718 show that inconel 625 can operate at higher temperatures. This makes it a better choice for exhaust systems and heat shields. Inconel 718 performs well at elevated temperatures but is limited to about 700°C.
Main Standards
You need to follow strict standards in aerospace manufacturing. Both inconel 718 and inconel 625 meet several international and industry-specific standards.
| Standard | Applicable Alloy |
|---|---|
| AMS 5599 | Inconel 625 |
| AMS 5666 | Inconel 625 |
| AMS 5837 | Inconel 625 |
| AMS 5832 | Inconel 718 |
| AMS 5664 | Inconel 718 |
| ASTM B 443 Gr 1 | Inconel 625 |
| ASTM B 446 Gr 1 | Inconel 625 |
| ASTM B 444/B 829 | Inconel 625 |
| ASTM B 705/B 775 | Inconel 718 |
| EN 2.4856 | Inconel 625 |
| ISO 15156-3 | Inconel 625 |
| NACE MR0175-3 | Inconel 625 |
Note: AMS 5832 and AMS 5664 are key for inconel 718 in high-strength, high-temperature aerospace parts. AMS 5599 and ASTM B 443 Gr 1 are common for inconel 625 in corrosive and high-temperature environments.
Aerospace Uses
You will find inconel 718 and inconel 625 in many aerospace components, but each alloy fits different roles based on its material properties.
Inconel 718:
- Turbine rotating parts (shafts, blades, discs)
- Airfoils for aerodynamic surfaces
- Supporting structures for engine and airframe
- Pressure vessels in rocket engines
Inconel 625:
- Exhaust systems and heat shields
- Engine thrust reversers
- Ducting systems exposed to corrosive gases
- Components in chemical processing within aircraft
When you need high strength and durability, inconel 718 is your best choice. If you require superior corrosion resistance and flexibility at higher temperatures, inconel 625 will serve you better. This performance comparison helps you match the right alloy to your aerospace needs.
Selection Criteria
Mechanical Strength & Temperature
You need to consider mechanical strength and high temperature resistance when choosing between inconel 718 and inconel 625 for aerospace applications. Both alloys can operate at maximum temperatures up to 980°C (1800°F). However, you will notice important differences in their performance at elevated temperatures and under extreme conditions:
- Inconel 718 offers higher mechanical strength, especially above 700°C. You can rely on this alloy for parts that must handle heavy loads and stress, such as turbine discs and shafts.
- Inconel 625 provides reliable durability in high-temperature environments, but its mechanical strength is lower than inconel 718. You might choose this alloy for components that need flexibility and resistance to deformation rather than maximum strength.
Tip: If your application demands high strength at high temperatures, inconel 718 is usually the better choice. For parts exposed to extreme conditions but not heavy mechanical loads, inconel 625 works well.
Corrosion Resistance
Corrosion resistance is a critical factor in aerospace, especially for components exposed to fuel, hydraulic fluids, or marine environments. You will find that inconel 625 stands out for its excellent corrosion resistance in a wide range of conditions. This alloy performs exceptionally well in hydraulic tubing and marine applications, where exposure to salt spray and aggressive chemicals is common.
Inconel 718 also resists corrosion, but it does not match the level of protection provided by inconel 625. Research shows that both alloys outperform standard stainless steel (like SS316L) in salt spray tests. After 200 hours in a 5% NaCl solution at 35°C, neither alloy showed harmful surface changes or significant weight loss. This makes both inconel 718 and inconel 625 suitable for extreme conditions, but you should select inconel 625 when corrosion resistance is your top priority.
Fabrication & Machinability
You must consider the machinability difference of inconel 625 and 718 when planning your manufacturing process. Both alloys are challenging to machine due to their tendency to harden quickly under mechanical stress. This property increases tool wear and requires advanced techniques.
| Alloy | Machinability Rating (AISI) |
|---|---|
| Inconel 625 | 17% |
| Inconel 718 | 12% |
Inconel 625 is slightly easier to machine than inconel 718, but both require specialized tooling and skilled operators. You may experience longer production times and higher costs because of these challenges. Welding also presents difficulties, but inconel 625 generally offers better weldability.
Note: The need for advanced manufacturing methods can extend lead times for aerospace projects using these alloys.
Cost & Availability
You should evaluate both the cost and availability of inconel alloys before making your final selection. Inconel 625 typically costs more per kilogram than inconel 718. Prices can vary by region and year, but here is a recent overview:
| Year | Inconel 625 (USD / lb) |
|---|---|
| 2021 | $14 – $20 |
| 2022 | $30 – $50 |
| 2023 | $22 – $35 |
| 2024 | $18 – $28 |
| 2025 | $22 – $40 |
| Region / Source | 2025 Range (USD per lb) |
|---|---|
| United States (distributor) | $30 – $40 |
| Europe (mill/distributor) | $32 – $42 |
| China (factory price, bulk) | $22 – $32 |
You may also face longer lead times due to the complexity of machining and welding inconel alloys. The need for specialized equipment and skilled labor can increase both production costs and delivery times. If your project has strict deadlines, you should plan for these factors when selecting between inconel 718 and inconel 625.
Applications for Inconel 718 and Inconel 625
Inconel 718 / UNS N07718 / W.Nr. 2.4668
You often choose inconel 718 for high-stress applications in aerospace. Nickel 718 gives you excellent fatigue strength, creep resistance, and impact toughness. This alloy keeps its strength at high temperatures, which makes it ideal for demanding environments. You will find nickel 718 in many critical aerospace components:
- Turbine discs that must handle extreme rotational forces
- Blisks (bladed disks) for jet engines
- Engine casings that protect internal parts from heat and pressure
- Engine-adjacent frame components that require both strength and durability
Nickel 718 performs well in application scenarios where you need resistance to repeated stress cycles and high temperatures. You can rely on this alloy for gas turbines, jet engines, and rocket motors. Its corrosion resistance also helps in aggressive environments, such as those found in the oil and gas industries.
Tip: When you need a material that resists deformation and fracture under sudden impacts, nickel 718 stands out as a top choice for aerospace applications.
Inconel 625 / UNS N06625 / W.Nr. 2.4856
You select inconel 625 when you need superior corrosion resistance and flexibility at high temperatures. Nickel 625 works well in aerospace components that face harsh chemical processing or thermal cycling. The following table shows how different aerospace parts benefit from inconel 625:
| Aerospace Component | Benefits of Inconel 625 |
|---|---|
| Gas Turbine Engines | High-temperature strength, oxidation resistance, fatigue resistance |
| Rocket Engines | High-temperature stability, resistance to thermal cycling |
| Heat Shields for Spacecraft | Exceptional heat resistance, oxidation resistance |
| Seals and Gaskets | High resistance to oxidation and thermal degradation |
Nickel 625 is also common in exhaust systems, ducting, and heat shields. You will see this alloy used in application scenarios where exposure to corrosive gases or saltwater is likely. Inconel 625 also finds use in the oil and gas industries, where its resistance to aggressive chemicals is valuable.
Note: If you need a material that can handle both high temperatures and corrosive environments, inconel 625 gives you reliable performance across many aerospace and industrial uses.
Heat Treatment
You can control the performance of Inconel 718 and Inconel 625 by choosing the right heat treatment method. This process changes the microstructure of each alloy, which affects strength, hardness, and resistance to stress. When you select a heat treatment method, you need to match it to your aerospace part’s requirements.
For Inconel 718, you often use aging, homogenization, and solution treatments. These steps help you boost mechanical properties and improve the alloy’s structure. The table below shows how each heat treatment method changes Inconel 718:
| Heat Treatment Process | Effect on Inconel 718 Mechanical Properties | Notes |
|---|---|---|
| Aging Process | Precipitation of γ″ and γ′ phases improves mechanical properties | Simple aging enhances properties for fine dendrite structure |
| Homogenization at 1180°C | Eliminates residual stress and introduces isotropic tensile properties | Higher temperature improves microstructure |
| Solution Treatment at 1050°C | Dissolves Laves phases, improves high-temperature stress rupture performance | Modifies long chain-like Laves phases to granular ones |
| Heat Treatment at 750°C | Precipitation of γ″ increases hardness | Hardness increased from 225 HV to 236 HV |
You will notice that Inconel 625 responds differently. Stress relief and annealing are common choices. These treatments help you control phase composition and hardness. Here is a summary for Inconel 625:
| Heat Treatment Process | Effect on Inconel 625 Mechanical Properties | Notes |
|---|---|---|
| Stress Relief at 870°C | Formation of δ phase, decreases lattice parameter of γ phase | Alters phase composition |
| Annealing at 1050°C | Fully dissolves δ phase, no effect on hardness | Maintains hardness |
| Annealing at 1150°C | Hardness decreases by approximately 10% | Higher temperature affects hardness |
| Heat Treatment at 750°C | γ″ precipitation increases hardness | Hardness increased from 225 HV to 236 HV |
Tip: You can fine-tune the properties of both alloys by adjusting the heat treatment method. Always check the specific needs of your aerospace application before you choose a process.
Decision Guide
Decision Tree
You want a quick way to choose between these two superalloys. Use this simple decision tree to match your aerospace needs:
- Do you need the highest possible strength at temperatures up to 700°C?
- Yes → Choose Inconel 718.
- No → Go to the next question.
- Will your part face extreme corrosion or chemical exposure?
- Yes → Choose Inconel 625.
- No → Go to the next question.
- Is your component exposed to temperatures above 700°C?
- Yes → Inconel 625 is better.
- No → Inconel 718 may be best.
- Do you need easier welding and fabrication?
- Yes → Inconel 625 offers better weldability.
- No → Both alloys are suitable.
When you compare inconel 718 vs. inconel 625, always start with your most critical requirement. This approach helps you avoid costly mistakes.
Checklist
Before you make your final choice, review this checklist. It will help you decide between inconel 718 vs. inconel 625 for your aerospace project:
- My part needs high strength at elevated temperatures (up to 700°C).
- My application faces aggressive corrosion or chemical attack.
- I require good weldability and easier fabrication.
- My budget can support a higher material cost.
- My design needs flexibility at very high temperatures.
If you check more boxes for strength and temperature, inconel 718 vs. inconel 625 leans toward 718. If you check more for corrosion, weldability, or extreme heat, inconel 625 is likely the better fit.
Tip: Always review your project’s environment and stress conditions. The inconel 718 vs. inconel 625 decision depends on matching alloy properties to your real-world needs.
You can see the main differences between Inconel 718 and Inconel 625 in their strength, temperature limits, and corrosion resistance. The table below highlights these key points:
| Property / Feature | Inconel 625 | Inconel 718 |
|---|---|---|
| Main Strength | Excellent corrosion resistance | High strength, good corrosion resistance |
| Max Operating Temp. | ~980 °C | ~700 °C |
| Tensile Strength | ~827 MPa | ~1240 MPa |
| Typical Applications | Marine, chemical, aerospace | Aerospace, power, tooling |
Choose your alloy by matching these properties to your project’s needs. Use the decision guide to select with confidence and ensure long-term performance in aerospace environments.
FAQ
What is the main difference between Inconel 718 and Inconel 625?
You will notice Inconel 718 gives you higher strength at elevated temperatures. Inconel 625 offers better corrosion resistance and flexibility. Choose Inconel 718 for heavy loads. Pick Inconel 625 for harsh chemical or marine environments.
Tip: Match the alloy to your most critical requirement.
Can you weld both Inconel 718 and Inconel 625 easily?
You can weld both alloys, but Inconel 625 is easier to weld. Inconel 718 may require special techniques to avoid cracking. Always use skilled welders and proper procedures for best results.
Which alloy costs more for aerospace projects?
You will usually pay more for Inconel 625. It costs more per pound than Inconel 718. Plan your budget carefully if you need large quantities of Inconel 625.
- Inconel 625: Higher cost
- Inconel 718: Moderate cost
How do you choose the right alloy for your aerospace part?
You should list your project’s needs. Focus on strength, temperature, corrosion, and fabrication. Use a checklist or decision tree. This approach helps you select the best alloy for your application.
Note: Always review your design and environment before making a final choice.
