Announcement: Pease be informed that the Colloquium will be cancelled.
Metal 3D printing is a collection of disruptive technologies that fabricate metal parts from 3D models, usually layer upon layer. Or, more generally, you can print any geometry you can dream of. Despite such an extreme degree of flexibility, the widespread use of metal 3D printing is currently limited by various defects and deleterious microstructures. They could impair the performance like corrosion resistance and fatigue life of the product. Our research focus is to understand their formation and evolution during the laser powder bed fusion (LPBF) process. LPBF is a dominant metal 3D printing process. In 2016, we built a LPBF simulator and integrated it with the high-speed x-ray imaging and diffraction techniques at the Advanced Photon Source. In 2017, we demonstrated the power of the platform and published our first paper in Scientific Reports (1). In 2019, we published the results of keyhole morphology evolution in Science (2) and fast spatter formation in Physical Review X (3). On 27 November 2020, we published the results of boundary and origin of keyhole porosity in Science (4). In this presentation, we will introduce the keyhole and keyhole porosity during laser melting. Three key points: one, keyhole widely exists in laser 3D printing of metals; two, the keyhole porosity boundary is smooth and sharp; three, in the dominant keyhole porosity mechanism, acoustic waves drive the rapid migration of the pores near the keyhole tip away from the keyhole.
1. C. Zhao, K. Fezzaa, R. W. Cunningham, H. Wen, F. De Carlo, L. Chen, A. D. Rollett, T. Sun*, Real-time monitoring of laser powder bed fusion process using high-speed X-ray imaging and diffraction. Scientific Reports 7, 3602 (2017).
2. R. Cunningham#, C. Zhao#, N. Parab, C. Kantzos, J. Pauza, K. Fezzaa, T. Sun, A. D. Rollett*, Keyhole threshold and morphology in laser melting revealed by ultrahigh-speed x-ray imaging. Science 363, 849-852 (2019).
3. C. Zhao, Q. Guo, X. Li, N. Parab, K. Fezzaa, W. Tan*, L. Chen*, T. Sun*, Bulk-Explosion-Induced Metal Spattering During Laser Processing. Physical Review X 9, 021052 (2019).
4. C. Zhao*, N. D. Parab, X. Li, K. Fezzaa, W. Tan, A. D. Rollett*, T. Sun*, Critical instability at moving keyhole tip generates porosity in laser melting. Science 370, 1080-1086 (2020).
Dr. Cang Zhao is currently an assistant professor at the Department of Mechanical Engineering at Tsinghua University. He received his Ph.D. degree in Structural Engineering from the University of California, San Diego in 2015, his master’s degree in Condensed Matter Physics from the University of Science and Technology of China in 2011, and his bachelor’s degree in Materials Science and Engineering from the University of Science and Technology Beijing in 2009. Prior to his current position, he worked as a postdoctoral researcher at the Advanced Photon Source of Argonne National Laboratory from 2016 to 2019. A few keywords could be used to summarize his research: metal additive manufacturing, cellular solids, and multiscale mechanics. He has published more than twenty peer-reviewed papers in journals such as Science and Physical Review X to date. In addition, he has achieved the Outstanding Postdoctoral Performance Award in Applied Science from Argonne National Laboratory and the President Award of the Chinese Academy of Sciences.
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