Monday, March 19, 2018
10:15 a.m., 3405 Engineering Building
Mississippi State University
Additive manufacturing (AM), as a process of fabricating 3D components in a layer-wise fashion, has great potential to revolutionize U.S. manufacturing in that it allows for on-demand generation of complex customized parts for extensive applications. However, the AM of metals introduces a melt pool and rapid thermal cycles that result in microstructures featured with anisotropy and porosity, thus deteriorating the mechanical properties of AM metallic builds. This presentation will discuss a phase-field centered multiscale model that real-time captures microstructure morphologies and porosity scenarios for given manufacturing processing variables, using selective electron beam melting of Ti-6Al-4V as an example. Upon experimental validation, it is found that, the development of the predominant grain structures in the thick and thin walls, i.e., the large vertical columnar <001>//Nz grains and slanted columnar grains with various grain orientations, respectively, can be attributed to the competition and collaboration between the thermal gradient and the crystallographically preferred grain growth. The analysis of printing parameters is then used to tailor the manufacturing conditions to achieve site-specific grain structure control. Two strategies, i.e., rolling induced plasticity-driven recrystallization and nucleant-controlled heterogeneous nucleation, are proposed to achieve the grain refinement. The preliminary efforts are also made to model the porosity evolution during the remelting of AM builds.
I will also talk about AM fabrication of piezocomposites which consist of a piezoelectric-ceramic phase and an elastic-polymer phase. Current piezocomposites cannot be achieved with controlled piezoelectric properties, due to the limited capability of traditional fabrication methods in carefully controlling the morphology of each phase. In this talk, I will present our recent research on computational design and AM fabrication of bi-continuous piezocomposites in which two phases are continuously interconnected in 3D. It is demonstrated the macroscopic piezoelectric properties of bi-continuous piezocomposites made by the AM-based fabrication process are functions of statistically porosity of ceramic phase, and two-phase interface connectivity. The research opens up the possibility of achieving piezocomposites with controlled piezoelectricity through tailoring the two-phase interface geometry, which may find applications for flexible electronics, wearable sensors, strain-tolerant hydrophone, etc
Dr. Lei Chen is an assistant professor at Mississippi State University currently. Dr. Chen received his BS and MS degrees from Huazhong University of Science & Technology, China in 2005 and 2007 respectively, and PhD degree from the National University of Singapore in 2012. Chen’s research interest is in the broad area of advanced manufacturing and materials design, with a focus of additive manufacturing of metals and piezoelectric composites. The research in the group is supported by NSF, ORAU, ARL, and ONR-SBIR. Chen has published over 60 authored or co-authored papers in top international journals including Nature, Nature Communications, Nano letters, Journal of Power Sources, Computer Methods in Applied Mechanics and Engineering, etc. Chen has received 1210 citations to date. He has received a number of awards from universities and organizations worldwide. Recent awards include the prestigious ASEE Southeastern Section New Researcher Award (2018), ORAU Ralph E. Powe Junior Faculty Enhancement Award (2017), Southeastern Conference Visiting Faculty Travel Award (2016), Y. Z. Hsu Scientific Paper Award (2015), Chinese Excellent Self-financed Student Abroad Award (2012), and President Graduate Fellowship Award at National University of Singapore (2009). He served as the NSF panelist and the reviewer of more than 20 international journals in the areas of computational mechanics, materials, energy and manufacturing. He has delivered more than 30 presentations in international conferences and local workshops or seminars.