题目：Can we tailor materials microstructure?

　　报告人：Dr. Suk-Joong L. Kang, president of KICET

　　单位：韩国陶瓷工程技术研究所
　　　　　(Korea Institute of Ceramic Engineering and Technology, KICET)

　　时间：12月15日（周五），上午10:00-12:00，

　　地点：李薰楼468室

　　摘要：Can we tailor materials microstructure?

　　Tailoring of microstructure has long been a fundamental issue in the international materials community because the microstructure considerably affects the properties of materials. For some cases, we want a fine microstructure down to a nanoscale; but, for some other cases, we want a coarse or a duplex microstructure with some abnormally large grains embedded in a fine matrix. Any microstructure we observe is the result of grain growth, which is a result of the migration of grain boundaries. Therefore, understanding the mechanism and behavior of boundary migration is critical for grain growth control and microstructure tailoring.

　　Recently, we found that boundary migration is governed by a mixed mechanism, diffusion or interface reaction of atoms. The migration of a rough (atomically disordered) boundary is governed only by diffusion, which has a linear kinetics with respect to the driving force. On the other hand, the migration of a (even partially) faceted (atomically ordered) boundary is governed by an interface reaction of atoms and the diffusion of atoms with a driving force smaller and larger than a critical value, respectively. For the regime of interface reaction control, the migration rate is insignificant, irrespective of the driving force, while the migration rate is linearly proportional to the driving for the regime of diffusion control. This mixed control of boundary migration exhibits nonlinear migration behavior of the boundary with respect to the driving force.

　　Based on the mixed control mechanism, we deduced the mixed mechanism principle of microstructural evolution, which is the coupling of the critical driving force for the appreciable migration of the boundary (Δg_c) and the maximum driving force for boundary migration (Δg_max) [1, 2]. By adjusting the relative value between Δg_c and Δg_max, we can prepare samples of the same system with different microstructures, ranging from fine to coarse and duplex. We can thus tailor materials microstructure. The generality of the microstructural evolution principle has been supported by many experimental results, not only in ceramics but in metals. Application of the principle has also been demonstrated for solid state conversion of single crystals [3].

　　References

　　[1] S.-J. L. Kang, et al., J. Am. Ceram. Soc. 92, 1464-71 (2009).
　　[2] R. K. Bordia, et al., J. Am. Ceram. Soc. 100, 2314-52 (2017).
　　[3] S.-J. L. Kang, et al., J. Am. Ceram, Soc. 98, 347-60 (2015).