Grain Boundary Mobility Control: A Case Study in Zirconia Ceramics
Massachusetts Institute of Technology
Competition between densification and coarsening is the key issue in ceramic sintering, which requires a rational design of grain boundary mobility within the applicable processing window. Using zirconia as a model system, we demonstrate a facile control of grain boundary mobility over orders of magnitude, via conventional state variables including temperature, atmosphere and electric field. Specifically, >1,000 times enhanced mobility can be obtained by (electro-)chemical reduction, indicating greatly accelerated cation diffusion by cation reduction and novel electron-phonon interactions on ion dynamics as proved by first-principles simulations. On the other hand, a rapid mobility quench has been observed in cubic zirconia, suppressing grain growth kinetics and enabling two-step sintering to fabricate nano-grain ceramics. A generalized mean-field growth theory echoes with our observations, addressing a critical role of multi-grain junctions which were previously unaware of. To conclude, we believe there is plenty of room in ceramic’s processing and microstructural control, where mechanistic understandings from continuum to atomistic scale are of vital importance.
Yanhao Dong is now a postdoctoral researcher at the Massachusetts Institute of Technology. He obtained his BS degree in materials science in 2012 from Tsinghua University, and his MS degree in materials science in 2014, his MS degree in applied mechanics in 2015, and his PhD degree in material science in 2017, all from the University of Pennsylvania. His PhD dissertation focused on cation diffusion in zirconia ceramics, covering from phenomenological sintering and grain growth experiments to continuum-level solution of transport and growth theory to atomistic simulation of defect energetics and kinetics. He received the inaugural Global Distinguished Doctoral Dissertation Award from the American Ceramic Society, Best Paper Award from Journal of the American Ceramic Society and Outstanding Reviewers Award from Scripta Materialia. His current research interest is on ceramics and functional oxides for energy application.