A research team led by Tao Sun, associate professor of materials science and engineering at the University of Virginia, using data obtained via experiments at the U.S. Department of Energy’s Advanced Photon Source (APS) has made new discoveries that can expand additive manufacturing in aerospace and other industries that rely on high-performance metal parts. Their results were published in the journal Science.
The results address the issue of detecting the formation of keyhole pores, one of the major defects in a common additive manufacturing technique called laser powder bed fusion, or LPBF.
Introduced in the 1990s, LPBF uses metal powder and lasers to three-dimensional (3-D) print metal parts. But porosity defects remain a challenge for fatigue-sensitive applications like aircraft wings. Some porosity is associated with deep and narrow vapor depressions which are the keyholes.
The formation and size of the keyhole is a function of laser power and scanning velocity, as well as the materials’ capacity to absorb laser energy. If the keyhole walls are stable, it enhances the surrounding material’s laser absorption and improves laser manufacturing efficiency. If, however, the walls are wobbly or collapse, the material solidifies around the keyhole, trapping the air pocket inside the newly formed layer of material. This makes the material more brittle and more likely to crack under environmental stress.
Sun and his team, including researchers from APS, Carnegie Mellon University (CMU), University of Wisconsin-Madison and DOE’s Kansas City National Security Campus, developed an approach to detect the exact moment when a keyhole pore forms during the printing process. “By integrating operando synchrotron x-ray imaging, near-infrared imaging, and machine learning, our approach can capture the unique thermal signature associated with keyhole pore generation with sub-millisecond temporal resolution and 100% prediction rate,” Sun said. The operando high-speed synchrotron x-ray imaging experiments were performed at the APS X-ray Science Division (XSD) Imaging Group’s 32-ID-B x-ray beamline of the APS, a Department of Energy Office of Science user facility at Argonne National Laboratory.