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You are invited to the lecture of Prof. Suk-Joong L. Kang (Korea Advanced Institute of Science and Technology). The lecture entitled "Normal and Abnormal Grain Growth in Polycrystals" will be on Friday, 30 August 2013 at 11 a.m. in the K-9 lecture room.

Normal and Abnormal Grain Growth in Polycrystals

Suk-Joong L. Kang

Materials Interface Laboratory, Department of Materials Science and Engineering,
Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu,
Daejeon, 305-701 Republic of Korea

Grain growth is a common phenomenon occurring during the fabrication of polycrystalline materials. Grain growth has conventionally been categorized into two types: normal and abnormal. Normal grain growth is characterized by a unimodal and invariable relative grain size distribution (relative size distribution of grains with respect to the average sized grain) as a function of the annealing time. The grain growth kinetics can be well described by the classical grain growth laws. On the other hand, abnormal grain growth is characterized by a bimodal size distribution of grains and a variable relative size distribution with the annealing time (nonstationary grain growth).

This presentation provides information about our recent theoretical as well as experimental results pertaining to grain growth behavior and its control in polycrystalline materials. A close correlation has been found between the grain growth behavior and the structure of the interface [1-4]. When the interface is faceted (atomically ordered), nonstationary grain growth occurs. For rounded (rough, atomically disordered) interfaces, normal (in another word, stationary) grain growth occurs. The difference in grain growth behavior for faceted and rough systems, nonstationary and stationary, is attributed to the difference in the dependence of the growth rate on the driving force: that is, linear for rough interface and non-linear for faceted interface [3-5]. According to theoretical as well as experimental results on the growth of faceted crystals, the nonlinear behavior exhibits a critical driving force, below which the rate is inconsiderable while above which the rate is linearly proportional to the driving force [6,7]. Grain growth behavior during annealing of polycrystals is predicted in terms of the maximum driving force Δgmax relative to the critical driving force Δgc: normal for Δgc = 0, pseudo-normal for Δgmax >> Δgc > 0, abnormal for Δgmax ≥ Δgc > 0, and stagnant for Δgmax << Δgc [5,8]. A number of experimental results support the above theoretical prediction of grain growth behavior, showing the generality of our suggested principle of microstructural evolution. Application of the microstructure evolution principle is also demonstrated for fabrication of single crystals.

[1] B. K. Lee et al, Acta Mater. 48 (2000) 1575; [2] S. Y. Chung et al, Acta Mater. 50 (2002) 3361; [3] B. K. Yoon et al, Acta Mater. 53 (2005) 4677; [4] Y. I. Jung et al, Acta Mater. 54 (2006) 2849; [5] S.-J. L. Kang et al, J. Amer. Ceram. Soc. 92 (2009) 1464; [6] S. D. Peteves and R. Abbaschian, Metall. Trans. A, 22 (1991) 1271; [7] S.-M. An et al, Acta Mater. 60 (2012) 4531; [8] Y. I. Jung et al, J. Mater. Res. 24 (2009) 2949.