Researchers observe metal 3D printing dislocations in real-time
Tracking the printing process with X-ray diffraction and directly measuring how and when dislocations form and spread
In a major scientific advance, researchers at the US Department of Energy’s (DOE) Argonne National Laboratory, Oak Ridge National Laboratory, and other universities have observed how the microstructure of metals changes in real-time during 3D printing. This breakthrough was made possible by Argonne’s Advanced Photon Source (APS), a DOE Office of Science user facility. The findings were published in Nature Communications.
Previously, scientists could only analyze the microstructures of 3D printed components after the printing process was finished.
“Metals are made of atoms arranged in ordered crystal structures,” said Tao Sun, the project’s lead investigator and a professor at Northwestern University who also holds a joint appointment at Argonne. “But under rapid heating and cooling, some atoms fall out of alignment. These defects – called dislocations – can strengthen or weaken the final part.”
Using beamline 1-ID-E at the APS, the team conducted 3D printing of 316L stainless steel, a commonly used structural alloy. They tracked the printing process with real-time X-ray diffraction, directly measuring how and when dislocations form and spread.
“Our analysis shows how powerful the APS is for studying defects that were previously only seen through after-the-fact analysis,” said Andrew Chuang, a physicist at APS. “This is the first time this real-time technique has been applied to this laser-based method to study the dislocation evolution in a metal wire.”
The data revealed that dislocations form early, just as the metal changes from liquid to solid. It was previously thought that they form later as stresses build up during cooling and solidification. A key factor was a specific reaction in which two solid phases form at the same time from the liquid, creating a high density of dislocations.
This deeper understanding could help engineers improve the strength and reliability of 3D printed parts. By adjusting printing variables, developers would be able to precisely control the formation of dislocations at the microscopic level. By this means, they could take full advantage of the dislocations’ beneficial attributes while minimizing the detrimental ones.
The insights gained could also spur the development of new alloys. Adjusting the chemical makeup of stainless steels – for example, by tweaking the ratios of chromium or nickel, or by adding elements like aluminum – can influence how dislocations form and how stress is distributed.
“This type of 3D printing could create customized metal parts that are reliable and extra-strong and would survive extreme conditions,” said Lin Gao, a postdoctoral researcher in the Nuclear Science and Engineering division at Argonne. “It may be key to building advanced metal components for next-generation nuclear reactors now being designed at Argonne and other labs.”
