The OpeN-AM experimental platform, installed at the VULCAN instrument at ORNL’s Spallation Neutron Source, features a robotic arm that prints layers of molten metal to create complex shapes. Image: Jill Hemman, ORNL/U.S. Dept. Of Energy.
The OpeN-AM experimental platform, installed at the VULCAN instrument at ORNL’s Spallation Neutron Source, features a robotic arm that prints layers of molten metal to create complex shapes. Image: Jill Hemman, ORNL/U.S. Dept. Of Energy.

By using neutrons to visualize the additive manufacturing process at the atomic level, scientists have shown they can measure strain in a material as it evolves and track how atoms move in response to stress.

“The automotive, aerospace, clean energy and tool-and-die industries – any industry that needs complex and high-performance parts – could use additive manufacturing,” said Alex Plotkowski, materials scientist in the Materials Science and Technology Division of Oak Ridge National Laboratory (ORNL) and lead scientist of the study. Plotkowski and his colleagues report their findings in a paper in Nature Communications.

ORNL scientists have developed OpeN-AM, a 3D printing platform that can measure evolving residual stress during manufacturing using the VULCAN beamline at ORNL’s Spallation Neutron Source (SNS), a US Department of Energy (DOE) Office of Science user facility. When combined with infrared imaging and computer modeling, this system provides unprecedented insight into material behavior during manufacturing.

Over the course of two years, the scientists conceived and produced the OpeN-Am platform for measuring strain in a material as it evolves, which determines how stresses will be distributed. They then used the OpeN-Am platform to measure how the atoms in low-temperature transformation (LTT) steel move in response to stress, whether induced by temperature or load.

Residual stresses are stresses that remain even after a load or the cause of the stress is removed; they can deform a material or, worse, cause it to fail prematurely. Such stresses are a major challenge for fabricating accurate components with desirable properties and performance.

“Manufacturers will be able to tailor residual stress in their components, increasing their strength, making them lighter and in more complex shapes,” Plotkowski said. “The technology can be applied to anything you want to manufacture.

“We have successfully shown that there is a way to do that. We are demonstrating we understand connections in one case to anticipate other cases.”

The scientists recently earned a 2023 R&D 100 Award for this technology.

In the study, they used a custom wire-arc additive manufacturing platform to perform what’s called operando neutron diffraction of an LTT metal at SNS. Using SNS’s VULCAN beamline, they processed the steel and recorded data at various stages during manufacturing and after cooling to room temperature. They then combined the diffraction data with infrared imaging to confirm their results.

The system was designed and built at the Manufacturing Demonstration Facility (MDF), a DOE Advanced Materials and Manufacturing Technologies Office user consortium, where a replicate system was also constructed to plan and test experiments before executing at the beamline.

SNS operates a linear particle accelerator that produces beams of neutrons to study and analyze materials at the atomic scale. The OpeN-Am platform allows scientists to peer inside a material as it’s being produced, literally observing the mechanisms at work in real time.

The LTT steel was melted and deposited in layers. As the metal solidified and cooled, its structure transformed, in what is called a phase transformation. When that happens, atoms rearrange and take up different space, and the material behaves differently.

Normally, transformations that happen at high temperatures are hard to understand when looking at a material only after processing. But by observing the LTT steel during processing, the scientists showed that they can understand and manipulate the phase transformation.

“We want to understand what these stresses are, explain how they got there and figure out how to control them,” Plotkowski said.

“These results provide a new pathway to design desirable residual stress states and property distributions within additive manufacturing components by using process controls to improve nonuniform spatial and temporal variations of thermal gradients around key phase transformation temperatures,” the authors write in the paper.

Plotkowski hopes scientists from around the world come to ORNL to do similar experiments on metals they would like to use in manufacturing.

This story is adapted from material from ORNL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.