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In the last decade, additive manufacturing has developed into a revolutionary technology that plays an important role in the fourth industrial revolution. Thanks to the design flexibility enabled by the technology, interest in additive manufacturing has grown significantly. A challenge with the method is that manufactured components can contain small voids, leaving them unfit for use. Sneha’s research now shows that it is possible to manufacture more reliable components through a highly streamlined post-processing.

Electron beam melting - new possibilities for production in difficult-to-machine materials

The possibilities for manufacturing components in hard materials, such as superalloys, have traditionally been limited. The process has been costly and required expensive tools with a short life cycle. Therefore, the industry's attention has now focused on the additive manufacturing process electron beam melting (EBM) which enables direct production of components with complex designs in the nickel-iron based superalloy Alloy 718.

- Alloy 718 is a very strong material that can withstand high temperatures, chemical attacks, and strong impact, Sneha says. Therefore, it can be used to advantage in, for example, aircraft engines where temperatures can rise upwards of 600 degree Celsius.

Demand for additively manufactured components in Alloy 718 is high in the aerospace and energy industry where design flexibility and short manufacturing times are of great importance. However, the as-produced components often contain imperfections that render them unreliable for the above demanding applications, but these imperfections can be removed through post-processing. This is where the focus of Sneha's research lies.

- Components manufactured through EBM are also lighter since less material is required for manufacturing in comparison to more traditional methods, she explains and continues, this can in the long run contribute to a reduced fuel consumption in the aerospace industry.

Post-processing to create reliability

It is common for EBM-manufactured components to contain certain defects, such as small pores. For the aerospace and energy industries to be able to use the components, with their extremely high-quality requirements, an additional process is needed before the components can be used, so-called post-treatment.

- The small pores that occur during EBM manufacturing make the components unreliable, Sneha explains. Therefore, I have investigated how the various stages of thermal post-treatments affect the structure of the materials at wide length scales.

In her brand-new dissertation, Sneha strengthens the limited knowledge about optimal thermal post-treatment of EBM-manufactured components in Alloy 718.

Part of the post-treatment process includes hot isostatic pressing (HIPing) and heat treatment. The HIPing method, in particular, involves placing EBM-manufactured components in a heated chamber to soften them, thereafter by applying a high gas pressure the components are densified.

- The pressure in the chamber presses the components with the same amount of pressure on all sides. This means that it retains its shape but becomes more compact, Sneha explains. The goal is to minimize the pores that have occurred during EBM-manufacturing.

A more efficient process that can save time and money

By experimenting with gas pressure, time, and temperature, Sneha has concluded that it is possible to successfully use post-treatment to increase the reliability of EBM-manufactured components.

Today, the whole post-treatment process of EBM-manufactured components takes around 25 hours, which according to Sneha's study is twice as long time as what is actually needed.

- My study shows that through the right post-treatment process, it is possible to remove the pores in EBM-manufactured components and thus making them very reliable. I have tried to treat several different types of structures, all of which have had a consistent result, Sneha explains. I have also found that it is possible to shorten the post-treatment time to about 10 hours, instead of 25 hours, she concludes.

The results of the study may be of great importance to the aerospace and energy industries, primarily in the form of reduced costs and lead times.

Read Sneha Goel's dissertation: “Thermal post-treatment of Alloy 718 produced by Electron beam melting

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