Inconel 718 (or Alloy 718) is a special type of high-strength superalloy with a nickel-chrome base that makes it resistant to corrosion, high pressure and extreme temperatures of up to 700°C.
The material is composed of 50-55 % nickel, 17-21% chromium, 4.75-5.5 % niobium and tantalum, and trace amounts of molybdenum, titanium, cobalt, aluminium, manganese, copper, silicon and other elements.
Because of its unique properties, Inconel 718 has become useful in a wide range of applications ranging from manufacturing operations to military equipment and the aerospace industry.
Properties of Inconel 718
With a melting point of 1430°C, Inconel 718 showcases effective resistance to heat and high temperatures. It also works well in cryogenic conditions, which shows the range of temperature resistance that this material possesses.
Natural heat protection
This nickel superalloy has an intrinsic ability to create a strong and stable oxide layer when exposed to heat. This natural passivation feature protects the material against damage.
The protective oxide layer gives this Inconel variant a significant amount of resistance to oxidation, thereby protecting it from corrosion.
High mechanical strength
At room temperature, the superalloy material exhibits a minimum of 725 MPa yield strength and 1035 MPa tensile strength. When Inconel 718 undergoes solution and precipitation treatment, these figures increase to 1035 MPa and 1240 MPa, respectively.
Exceptional welding quality
Other Inconel alloys are difficult to weld due to brittleness and cracking at the exact welding point. However, Inconel 718 has been created to address this issue, whether electron-beam or arc welding is used.
Good malleability and machining quality
Most Inconel alloys tend to experience strain hardening when machining or shaping is attempted. Inconel 718 is different-- it’s easier to machine using a hard cutting implement through a slower cutting mechanism.
Roll threading of this superalloy is possible through 700°C induction heating after fully aging the material.
Production and processing
Inconel 718 may be produced through the following processes:
- Annealing: The metal is exposed to heat and then gradually brought down to lower temperature. This gives the material its strength and resistance to stress.
- Precipitation hardening: Also called age hardening or precipitation heat treatment, this method boosts the alloy’s strength by introducing impurities before heating.
In annealing – or also called solid solution strengthening – metal components are dissolved completely so that they will precipitate properly to give Inconel 718 the strength that it is designed to have.
In precipitation strengthening, nickel and niobium combine to form gamma double prime (or Ni3Nb). Extreme heat at above 800°C causes the nickel phases to precipitate.
From this, Inconel 718 may be processed into custom shapes and orientations when machined above 540°C.
Applications of Inconel 718
Inconel 718 has become associated with 3D printing technology, as this alloy works effectively in printing parts and components for a wide range of industries. Several studies have looked into the use of the superalloy in the additive manufacturing (AM) industry and further enhancements to maximise its features.
Gas turbine engine parts
Because of its efficient weldability and heat resistance, the superalloy has become an integral component of gas turbine engines.
Aerospace and aircraft manufacturing
Due to the strength and resistance of the material, Inconel 718 has become a popular component for turbojet engine parts such as compressor casings, discs and fan blades. The superalloy has also found its way into the production of rocket engines, especially with the alloy’s high heat resistance. This is the primary reason why Inconel 718 comprises about half of the components in conventional aircraft engine parts.
This Inconel variant works well in hot environments, and so it’s a natural fit for extreme heat applications such as metal die casting. Other non-ferrous metals are more popular in this industry but Inconel 718 has more than enough toughness to protect itself from damage. As a result, dies or die holders made of Inconel 718 last longer and resist deformation better.