Inconel 625 and Inconel 718 are high-performance nickel superalloys that have been increasingly utilized in metal 3D printing. Their nickel-chromium base composition renders them highly resistant to corrosion and high temperatures. Their excellent mechanical, thermal, and corrosion properties have enabled their use in highly demanding applications, such as aerospace, industrial manufacturing, and military equipment.
Despite the fact that these nickel-based alloys are relatively difficult to machine, 3D printing’s capacity to realize complex configurations with minimal material usage can help create lightweight parts at near-net shape, which minimizes the need for machining. For that reason, Inconel 625 and 718 have become materials of interest for additive manufacturing.
But first, what exactly are Inconel 625 and 718? What is the difference between the two metal alloys? And how are they 3D printed?
Inconel 625 vs Inconel 718
Inconel is a trademark of Special Metals Corporation that comprises a family of over twenty nickel-based superalloys. These superalloys are high-performance alloys characterized by exceptional strength, high heat- and corrosion resistance, and good weldability.
Inconel 625 was developed back in the mid-20th century, as there was high demand for high-strength materials that could be used in steam power plants and piping. This demand led researchers to test chemical compositions that would guarantee high strength, such as mixing molybdenum and niobium with nickel. During the development of Inconel 625, researchers accidentally discovered Inconel 718, which proved highly useful for tough applications like airplane engines.
The difference between Inconel 625 and 718
Inconel 625 and Inconel 718 share many properties of the Inconel family. However, the key difference between them is that the main feature of Inconel 625 is high corrosion resistance, while that of Inconel 718 is high strength. Each of the two alloys has its own functions and cannot take the place of the other.
The following table shows how the two alloys fare against one another.
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Chemical composition (main elements) |
Ni |
58 – 71% |
Ni: ~ 53% |
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Cr |
21 – 23% |
19% |
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Mo |
8 – 10% |
3% |
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Fe |
5% |
18 – 18.5% |
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Nb+Ta |
3.2 – 3.8% |
5% |
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Density (23 °C) |
8.7 g/cm³ |
8.22 g/cm³ |
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Tensile strength (23 °C) |
810 – 920 MPa |
1034 – 1276 MPa |
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Yield strength (23 °C) |
330 – 460 MPa |
827 – 1034 MPa |
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Melting point |
1290 – 1350 °C |
1260 – 1335 °C |
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Operating temperature |
~ 1000 °C |
~ 700 °C |
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Heat treatment |
Inconel 625 is strengthened via solid solution |
Inconel 718 is strengthened via precipitation hardening, |
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Corrosion resistance |
Inconel 625 has lower Fe content than Inconel 718, which Since Ni, Cr, and Mo are elements with excellent |
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3D printing process |
Powder bed fusion (PBF) processes, mainly selective laser |
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Mean particle size (D50) of |
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How Inconel 625 and Inconel 718 are used in 3D printing
The most appropriate 3D printing process for Inconel nickel alloys is powder bed fusion (PBF), in which the alloys would be available in powder form. PBF is an additive manufacturing (AM) process that uses a high-energy power source, like a laser, to fuse powder material and create a three-dimensional object.
First, a layer of Inconel powder is spread over the bed of the 3D printer. Based on a computer-aided design (CAD) model that defines the shape of the part to be printed, a laser hits the powder and fuses the first layer of the model. The powder bed is then lowered to allow for a new layer of powder material to be spread over the previous layer. The laser continues to fuse the powder layer by layer as more powder is added over previous layers. This process continues until the whole model is constructed. The unfused powder is then removed in the post-processing stages and reused to manufacture the next model.
The two techniques under PBF that can be applied to Inconel 625 and 718 are selective laser melting (SLM) and selective laser sintering (SLS) – also known as direct metal laser sintering (DMLS).
SLM uses a high-energy laser to heat the nickel alloy powders above their melting point, causing them to melt and fuse, thus forming near-net-shape objects with high relative density.
On the other hand, SLS applies a laser onto the nickel alloy powder to fuse the targeted particles atomically at a temperature slightly below their melting point. This results in a specifically-shaped, high-density layer of fused powder that solidifies upon cooling.
For more information on SLM, SLS, and other PBF processes, click here.
3D printing Inconel 625 and Inconel 718 is quite cost-effective compared to the conventional, subtractive manufacturing processes, largely thanks to its ability to construct parts with minimal material usage and little to no waste.
In addition to that, 3D printing allows for lightweight products with designs that are difficult or even impossible to manufacture using traditional processes, all the while maintaining high mechanical, thermal, and corrosion properties. This results in a high strength-to-weight ratio that is vital for application areas that require lightweight, such as aerospace.
3D printing also reduces the need for machining, which is particularly important considering the low machinability of Inconel alloys. Nickel alloys are typically difficult to machine because of their high toughness and high hardness. They quickly work-harden, and the increasing hardening effect slows down further machining. Besides, warping may arise during the machining of small parts under high pressure.
What are Inconel 625 and Inconel 718 used for?
Thanks to their extremely high strength and high corrosion resistance, Inconel 625 and Inconel 718 have found their way into application areas, where they can easily outperform other materials, such as traditional steel.
Inconel 718 began in the aerospace industry because of its high strength and high-temperature resistance. It has become a very common material in that field that it now accounts for up to half the weight of a modern aircraft turbojet engine.
On the other hand, Inconel 625 found itself in applications that undergo corrosive conditions, such as the marine industry. Sea salt environments are highly corrosive. So, materials have to have extremely high corrosion resistance to withstand the effects of such corrosive environments.
Inconel 718 is commonly used in components within the following industries:
- Aerospace industry
- Automotive industry
- Power generation
- Welding products
- Marine industry
- Oil & Gas industry
- Petro processing
Inconel 625 is commonly used in the following application areas:
- Aerospace industry
- Chemical Processing
- Marine industry
- Oil & Gas industry
- Petro Processing
- Pollution & Waste
- Power Generation