ADVANCED MATERIALS & PROCESSES | JANUARY/FEBRUARY 2024 48 3D PRINTSHOP MICROSTRUCTURAL INFO IN REAL TIME Researchers from Cornell University were able to look at the microstructure of a 3D-printed metal alloy as it was being printed to study thermomechanical deformation, including bending, fragmentation, and oscillation. “There’s a lot of information missed by conducting only postmortem characterizations,” says Atieh Moridi, assistant professor at Cornell. “Now we have tools to be able to watch these microstructural evolutions as they are happening. We want to be able to understand how these tiny patterns or microstructures are formed because they dictate everything about performance of printed parts.” The group focused on a form of 3D printing in which a powder, in this case, the nickel-based superalloy IN625, is applied via nozzle and melted by a high-power laser beam, then cools and solidifies. Because it is not feasible to access high-energy x-rays in the lab, the researchers created a portable twin of their 3D-printing setup and brought it to the Center for High Energy X-ray Sciences at the Cornell High Energy Synchrotron Source (CHEXS@CHESS). During the experiment, a focused x-ray beam was sent into the hutch, where it passed through the IN625 as it was heated, melted, and cooled. A detector on the other side of the printer captured the patterns of diffraction that result from the x-rays interacting with the material. Typically, researchers would try to consolidate the amount of diffraction data to analyze it; but the team decided to study the raw detector images which provided a richer, holistic picture of how the IN625 took shape, revealing “unique features that most of the time we’re missing,” Moridi said. The group identified key microstructural features that were created by the process’s thermal and mechanical effects, including: torsion, bending, fragmentation, assimilation, oscillation, and interdendritic growth. cornell.edu. PRINTED MATERIAL GLOWS UNDER STRESS 3D-printed shapes made with a solution that includes bioluminescent materials glow in response to mechanical stresses such as compression, stretching, or twisting. Engineers at University of California San Diego combined bioluminescent dinoflagellates and a seaweed-based polymer called alginate to form a solution, which was then processed with a 3D printer to create a diverse array of shapes, such as grids, spirals, spiderwebs, balls, blocks, and pyramid- like structures. The 3D-printed structures were then cured as a final step. When the materials are subjected to compression, stretching, or twisting, the dinoflagellates within them respond by emitting light. This response mimics what happens in the ocean, when dinoflagellates produce flashes of light as part of a predator defense strategy. In tests, the materials glowed when the researchers pressed on them and traced patterns on their surface. The materials were even sensitive enough to glow under the weight of a foam ball rolling on their surface. The greater the applied stress, the brighter the glow. The researchers were able to quantify this behavior and developed a mathematical model that can predict the intensity of the glow based on the magnitude of the mechanical stress applied. “This current work demonstrates a simple method to combine living organisms with non-living components to fabricate novel materials that are self-sustaining and are sensitive to fundamental mechanical stimuli found in nature,” says Chenghai Li, a mechanical and aerospace engineering Ph.D. candidate at UCSD. The researchers envision that these materials could potentially be used as mechanical sensors to gauge pressure, strain, or stress. Other potential applications include soft robotics and biomedical devices that use light signals to perform treatment or controlled drug release. ucsd.edu. Schematic showing the three major stages of solidification during AM of IN625. Courtesy of A. Dass et al./Cornell University. These 3D-printed soft, living materials glow in response to mechanical stress, such as compression, stretching, or twisting. Courtesy of UC San Diego Jacobs School of Engineering.
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