What is the difference between Inconel 625 and 718? - Knowledge

What is the difference between Inconel 625 and 718?

Inconel 625 and Inconel 718 are high-performance nickel-based superalloys that are increasingly being used in metal 3D printing. Their nickel-chromium-based composition makes them highly resistant to corrosion and high temperatures. Their excellent mechanical, thermal, and corrosion properties enable their use in demanding applications such as aerospace, industrial manufacturing, and military equipment.

Although these nickel-based alloys are relatively difficult to machine, 3D printing enables complex configurations with minimal material usage, which helps to create near-net-shape, lightweight parts, minimizing the need for machining. As a result, Inconel 625 and 718 have become popular materials for additive manufacturing.

What is the difference between Inconel 625 and 718?

But first, what exactly are Inconel 625 and 718? What is the difference between these two metal alloys? How are they 3D printed?

Inconel 625 vs. Inconel 718
Inconel is a trademark of Special Metals Corporation and encompasses more than two dozen nickel-based superalloys. These superalloys are high-performance alloys that offer excellent strength, high heat and corrosion resistance, and good weldability.

Inconel 625 was developed in the mid-20th century because of a high demand for high-strength materials that could be used in steam power plants and pipelines. This demand prompted 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 to be very useful for demanding applications such as aircraft engines.

Differences between Inconel 625 and 718
Inconel 625 and Inconel 718 share many common properties of the Inconel family. But the key difference between the two is that the main property of Inconel 625 is strong corrosion resistance, while the main property of Inconel 718 is high strength. The two alloys have their own roles and cannot replace each other.

The following table shows how the two alloys fare against one another.

		Inconel 625	Inconel 718
Chemical composition (main elements)	Ni	58 – 71%	Ni: ~ 53%
	Cr	21 – 23%	19%
	Mo	8 – 10%	3%
	Fe	5%	18 – 18.5%
	Nb+Ta	3.2 – 3.8%	5%
Density (23 °C)		8.7 g/cm³	8.22 g/cm³
Tensile strength (23 °C)		810 – 920 MPa	1034 – 1276 MPa
Yield strength (23 °C)		330 – 460 MPa	827 – 1034 MPa
Melting point		1290 – 1350 °C	1260 – 1335 °C
Operating temperature		~ 1000 °C	~ 700 °C
Heat treatment		Inconel 625 is strengthened via solid solution strengthening, which makes it suitable for solution treatment.	Inconel 718 is strengthened via precipitation hardening, which makes ageing treatment the appropriate heat treatment.
Corrosion resistance		Inconel 625 has lower Fe content than Inconel 718, which means higher Ni, Cr, and Mo content. Since Ni, Cr, and Mo are elements with excellent corrosion properties, Inconel 625 tends to have higher corrosion resistance than Inconel 718.
3D printing process		Powder bed fusion (PBF) processes, mainly selective laser melting (SLM) and selective laser sintering (SLS)
Mean particle size (D₅₀) of metal powder		~ 31 – 32 µm	~ 13.6 – 15 µm