Advancing the understanding of metal additive manufacturing via physical simulation and in situ transmission electron microscopy: a viewpoint

The complex microstructure evolution and heterogeneities in metal additive manufacturing (AM) continue to delay the adoption of AM parts by additional industries. Achieving uniform and superior properties in AM parts requires better fundamental understanding of the microstructural evolution. A suitable pathway to gain such understanding is via in situ techniques such as high-speed X-ray imaging, high-resolution infrared cameras, or via synchrotron and neutron diffraction. However, these methods are complex and resource intensive. Modeling may be a more economical avenue, yet, to make these models more robust and reliable, data from in situ techniques are often required. We believe that in some cases, physical simulation methods originally developed for research on conventional processing such as forging, rolling, and welding may provide similar insights. This viewpoint article discusses existing experimental methods for tracking the microstructure evolution during AM in lab-scale settings, focusing on Ni-based superalloys as a case study. The proposed physical simulation methods include the Gleeble thermo-mechanical simulator, dilatometry, and the arc-melting heat treatment technique. These methods can also be integrated into various X-ray, synchrotron, and neutron diffraction set-ups. We discuss how insights derived from thermo-kinetic modeling can underpin the experimental observations from physical simulations. Last, in situ transmission electron microscopy is evaluated as a powerful method with unparalleled resolution for observing the microstructure evolution directly during simulated AM processes. We believe that these methods can be extended to other alloy systems, enhancing scientific understanding, and streamlining the efficient development of AM parts with superior and more uniform properties, promoting the more widespread adoption of AM.