Friday, April 22, 2022 10am to 11am
Virtual Event
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Abstarct:
Zirconia-based shape memory ceramics represent a distinct family of shape memory materials due to their ability to reversibly transform between tetragonal and monoclinic phases. Compared to shape memory metal alloys, shape memory ceramics possess much higher transformation stresses with a larger hysteresis and a broader range of tunable transformation temperatures, rendering them great promise for niche applications involving high-temperature actuation or high energy dissipation. The shape memory and superelastic effects of zirconia have been demonstrated in the material form of micro-pillars and micro-particles. However, owing to the intrinsic brittleness and the large volume change upon martensitic transformation, scaling shape memory ceramics up for bulk applications has been extremely challenging. Here, we explore the scaling-up of shape memory ceramics by design and control of the mesostructure, to match the mesoscale characteristic length scale with the microstructure. This strategy minimizes the triple junction among grains and therefore the mechanical constraint upon martensitic transformation, likely enabling shape memory and superelastic functionalities without catastrophic failure. We apply this design philosophy to various material forms of shape memory ceramics, including granular packings, micro-architectures, and metal matrix composites, which are fabricated via chemical synthesis followed by state-of-the-art additive manufacturing approaches. In addition to confirming martensitic transformation in these bulk structures upon thermal and mechanical stimulation, we find the transformation mode significantly deviating from their monolithic polycrystalline counterpart. The latter features a macroscopically discontinuous transformation mode with conspicuous peaks in differential scanning calorimetry and plateaus in stress-strain curves, whereas the mesostructure engineered materials exhibit a progressive mode with the transformation volume continuously changing with temperature or stress. Such a change in the transformation mode is shown to originate from the heterogeneous distribution of driving force and reduction of the nucleation barrier owing to mesostructure engineering.
Biography:
Hang Z. Yu is an Assistant Professor of Materials Science and Engineering at Virginia Tech. He received his bachelor’s degree in physics from Peking University in 2007 and his Ph.D. degree in materials science and engineering from Massachusetts Institute of Technology in 2013. The primary interest in Dr. Yu’s research group at Virginia Tech lies in advanced manufacturing of structural metals and multi-functional metal matrix composites, e.g., those based on shape memory ceramics. In particular, Dr. Yu is a research pioneer of solid-state additive manufacturing using additive friction stir deposition, having written the first book on the topic, which will be published by Elsevier in July 2022 (https://www.elsevier.com/books/additive-friction-stir-deposition/yu/978-0-12-824374-9). Dr. Yu’s research has been recognized by the ICTAS Junior Faculty Award and American-Made Challenges prizes.
Virtual Event
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