Tailoring Polycrystalline Microstructures by Use of Interface Structure Transition

ChEMS Seminar

Featuring Suk-Joong L. Kang, Ph.D.
Materials Interface Laboratory
Department of Materials Science and Engineering
Korea Advanced Institute of Science and Technolgy

Location: Engineering Lecture Hall, Room 110
Free and open to the public

Recent investigations on microstructural evolution in polycrystalline materials, in particular ceramics, show that there exists a close correlation between the evolution of microstructure and the structure of interfaces. When an interface is faceted (atomically ordered), suppressed (stagnant) or abnormal grain growth (SGG or AGG) occurs. The systems in this category include BaTiO3, SrTiO3, WC-Co, Si3N4 and TiC. For non-faceted (atomically disordered) interfaces, normal grain growth (NGG) occurs. The examples which exhibit NGG are BaTiO3 at a low oxygen partial pressure, NbC-Co-B and MgO-doped Al2O3. The difference in microstructural evolution for faceted or non-faceted systems is attributed to differences in the dependency of interface mobility with driving force; that is, variable for faceted systems and invariable for non-faceted systems. As the growth (dissolution) rate of a grain is a product of driving force and interface mobility, control of polycrystalline microstructure should be possible via proper control of the two parameters. The interface structure, which is represented by the step free energy of the interface, is governed by thermodynamic parameters, including temperature and chemistry. As the driving force comes from the difference in curvature among grains, it is governed by the average size and size distribution of grains. This presentation provides our recent experimental and theoretical results pertaining to microstructure evolution and control in polycrystals. It will be demonstrated that proper control of interface structure (step free energy) in conjunction with the driving force can result in the development of various types of microstructure, ranging from ultra fine and moderately sized to duplex, in single-phase as well as two-phase systems. The principles of microstructural design of polycrystalline materials are suggested.