Feature published in 3D ADEPT MAG in September–October 2020, then online in January 2021. The ExOne interview reflects that period. Editorial clarifications correct material characteristics and distinguish test specimens from installed components.
Additive manufacturing of superalloys is of interest to aerospace, energy and nuclear applications, where some components face demanding thermal and mechanical conditions. Inconel 718 is among the materials considered for these uses.
Superalloys are valued particularly for their mechanical performance at elevated temperatures. Nickel-based alloys, including Inconel 718, are an important family in metal AM; they are not the only alloys that can be processed.
This feature examines material properties, processing routes and selected applications. Choosing an alloy does not remove the need to qualify the part, process and treatments for its intended use.
Introducing Inconel 718
Inconel 718 (IN718) is a precipitation-hardenable nickel-chromium-iron superalloy. Its history predates metal AM: the alloy’s early development does not mean that it was already being 3D printed in the 1960s.
Mechanical performance depends on metallurgical condition, processing and heat treatment. Values for a conventional product are therefore not guaranteed minima for every printed part.
The Special Metals datasheet gives a melting range of 1,260–1,336°C. This does not define an allowable service temperature or establish suitability for cryogenic use.
The 2020 ExOne powder datasheet lists 50–55% nickel, 17–21% chromium, 4.75–5.5% niobium plus tantalum and 2.8–3.3% molybdenum, with iron forming the main balance. Molybdenum is therefore not merely a trace element.
Inconel 625 is another nickel-chromium alloy, strengthened mainly by molybdenum and niobium in solid solution. Its composition and strengthening mechanism differ from those of 718. The grades are not interchangeable, and comparing them requires more than price or iron content.
Processing Inconel 718
Inconel 718 can be processed by laser powder bed fusion (PBF-LB/M) or electron beam powder bed fusion (PBF-EB/M). Binder jetting is another route: printing is followed by debinding and sintering, rather than complete powder melting during the printing step.
The process, parameters and subsequent treatments influence part microstructure and performance. Assessment therefore needs to cover the complete manufacturing chain.
In the interview for this feature, Kyle Myers, then ExOne’s R&D manager, explains the supplier’s approach. On 5 August 2020, ExOne announced Inconel 718 qualification at the “Third-Party Qualified” level of its own programme, bringing its qualified-material count to 22.
Related coverage: our report on ExOne’s announcement.
This supplier qualification is not blanket approval for aerospace or nuclear use. Compliance still needs to be demonstrated for the component and its specification.
The manufacturer of binder jetting systems does not develop their own unique chemistries and powders. As per the words of Myers, they “mostly develop processing parameters that work for traditional materials and commonly used powders”. “These traditional materials are qualified to known standards which most of our customers are familiar with, which allows them to adopt our manufacturing process for their application quicker. Therefore, any customer that already designs a part, for their application with the inherent physical and mechanical properties to that specification, can insert binder jetting into their manufacturing process. Other customers may want to take advantage of AM, but work with a similar alloy to In718. They will need to do their homework to make sure the specifications of In718 can fit their specific application”, Myers told 3D ADEPT Media.
Processing history, including scan strategy, geometry and thermal cycles, influences microstructure. Treatments must be defined for the part and process concerned. ASTM F3055-14, cited here in its historical context, covers UNS N07718 produced by full-melt powder bed fusion using a laser or electron beam.
Its scope is not limited to stress relief and hot isostatic pressing: it also addresses manufacturing plans, feedstock, chemistry, properties and inspection. It does not automatically cover binder jetting. Supplier and purchaser need to establish the requirements and edition applicable to their project.
Applications of Inconel 718
Material selection depends on service temperature, loading, corrosion and inspection requirements. High-temperature strength alone does not establish suitability for every tool exposed to extreme heat.
Turbine-engine discs and casings are among the applications associated with the alloy. For a printed aerospace part, grade, build orientation, treatments and qualification need verification; not every turbine blade is made from Inconel 718.
In her 2019 doctoral thesis at the University of Manchester, Faye McCarthy investigates the repair of Inconel 718 aeroengine components using laser blown powder deposition. Her research examines how process parameters affect defects and microstructure in the repaired regions.
Additive repair is an option for selected worn components. Its applicability depends on the substrate, damage, deposition process and repair validation. Locally replacing material does not by itself establish that a blade can return to service.
The alloy is also of interest for space propulsion and research into nuclear materials. In the latter field, alloy tests must be distinguished from the actual installation of a component.
In a 4 May 2020 announcement, Westinghouse reported installation of a thimble plugging device in Exelon’s Byron Unit 1 reactor during the spring 2020 refuelling outage.
Editorial clarification: the NEI technical report published in December 2021 distinguishes irradiated 316L steel and alloy 718 test specimens from the installed device, which used 316L steel. This example therefore does not establish installation of an Inconel 718 component at Byron.
The report describes a hybrid component: elements produced by laser powder bed fusion on a conventionally manufactured baseplate. The programme included testing and qualification specific to that component.
Other developments cited in the feature concern bottom nozzles and fuel-assembly grids, exploring new geometries and hydraulic behaviour. Such design work should not be equated with deployment of every component mentioned or with general validation of Inconel 718 for nuclear service.
This feature was first published in the September–October 2020 issue of 3D ADEPT MAG.
THE 3D ADEPT WEEKLY NEWSLETTER
The industry moves fast. Stay ahead.
Every week, the latest additive manufacturing news, in-depth features and real-world applications, straight to your inbox. Plus, be the first to know when a new issue of 3D ADEPT Mag is out.
Free · One email a week · Unsubscribe anytime
Clicking loads our email provider’s sign-up form, including its analytics and Google’s anti-bot protection. You’re only subscribed if you complete the sign-up. Read our privacy policy.