Download Normal and Abnormal Grain Growth in Polycrystalline Materials Suk

Normal and Abnormal Grain Growth in Polycrystalline Materials
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
[email protected]
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.
Grain growth behavior during sintering 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[5,6]. A number of
experimental results support the above theoretical prediction of grain growth behavior,
showing the generality of our suggested principles of microstructural evolution. Application
of the microstructure evolution theory is also demonstrated for fabrication of polycrystals
with desired microstructures.
[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] Y. I. Jung et al, J. Mater. Res. 24 (2009) 2949