A collaborative effort of University of Tennessee and Oak Ridge National Laboratory (ORNL) researchers forged a 2023 R&D 100 Award for an innovative process that improves longevity for 3D-printed metal goods.
Suresh Babu, UT-ORNL Governor’s Chair and senior advisor for research and STEM workforce development initiatives, and Alex Plotkowski, senior staff scientist at ORNL, led the team in developing OpeN-AM, a platform for performing operando neutron (OpeN) diffraction studies of metals during additive manufacturing (AM), also known as 3D printing.
They published their results, “Operando Neutron Diffraction Reveals Mechanisms for Controlled Strain Evolution in 3D Printing,” in August in Nature Communications. Their method provides a new pathway to tailor residual stress states and property distributions—improving fatigue life and resistance to stress-corrosion cracking—within 3D-printed components, and to qualify parts for large-scale structures relevant to energy systems.
“The residual stress is a locked-in stress within a material,” said Babu. “As long as they are not detrimental, you’re okay. For example, your smartphone glass has residual stresses—on the top, they have a compressive stress. That’s why we if drop it, it doesn’t crack. So, the residual stresses are not necessarily bad. But what is the sign of the residual stress? Whether it’s compressive or tensile is very important.”
A material’s inherent stress areas can impact the overall 3D printed part as the layers of material are heated, stacked, and cooled in the printing process. Increases in tensile stress can reduce the load capacity of the material, so it is vital to identify where it occurs.
“Neutron diffraction has been used for a long time to measure the lattice strain in materials,” said Plotkowski, who worked on other AM projects as a post-doc for Babu before joining ORNL. “However, we realized that it was important to understand the evolution of those strains during additive manufacturing. Measuring only the final state does not always give enough insight into those mechanisms that occur during processing.”
“What we have developed is a methodology in which we can put the AM process in a neutron beam line and while we are making the part, the neutron beam line will be extracting both elastic and plastic strains,” said Babu. “That way, we can develop models that are well-calibrated and can be used for other structures. This unique experimental system is our innovation.”
The team designed a custom additive manufacturing system to suit the needs of the OpeN-AM experiments, which took place within the VULCAN beamline at ORNL’s Spallation Neutron Source.
“We used a robotic arm and welding equipment to deposit material, and added infrared cameras to track the temperature,” said Plotkowski. “Then we performed the experiment, simultaneously depositing material, measuring the temperature distribution, and collecting neutron diffraction data in three different detectors.”
Their system provides unparalleled insight into the evolution of phase transformations and stressors that occur during the additive manufacturing process. New possibilities abound in knowing how these phenomena behave.
“Future research may go in two directions,” said Plotkowski. “First, we will need to understand in more detail the response of the material for different geometries or other variations in processing. That information can help to inform industrial-scale processing. At the same time, this technique could be used to investigate a whole variety of other materials, each with their own properties and phase transformations. We could even use this as a tool for designing new materials.”
The team will be honored at the 2023 R&D 100 gala banquet on November 16 in San Diego. Often referred to as the “Oscars of Innovation” and the “Nobel Prize of Engineering,” these awards honor the 100 most innovative technologies of the past year. The program, established over 60 years ago, is the only science and technology awards competition that recognizes new commercial products, technologies, and materials for their technological significance that are available for sale or license.
Randall Brown (865-974-0533, firstname.lastname@example.org)