세미나안내

[2015 10 01] 특별세미나 Prof. Sung Gyun Ki

Phase-field Model for Grain Boundary Segregation

MSE Graduate Students and Researchers

관리자 | 2015.09.30 11:01 | 조회 1477


Reception: MSE Graduate Students and Researchers

Reference: MSE Professors

Subject: MSE Special Seminar_ Prof. Sung Gyun Kim

 

 Date: 2015. 10. 01(Thu), 16:30 ~ 17:30

 Place: Science Building, Room.301

 Title: Phase-field Model for Grain Boundary Segregation

 Speaker: Prof. Sung Gyun Kim(Kunsan Univ.)

Host of a Seminar: Prof. Byeong-Joo Lee

Speaker Language: KOREAN

 

Abstract

Impurity atoms when segregated at grain boundary (GB) regions can dramatically change the physical and chemical properties of GBs. A typical example is a remarkable enhancement of the thermal stability in the nanocrystalline grain structure when the solute atoms are segregated at GBs. This thermal stability appears to be attributed to the GB energy reduction and/or solute drag effect (retarded GB mobility) by the segregation. Gibbs thermodynamic approach where GB is assumed to be a mathematically sharp interface has been employed for thermodynamic treatment of GBs with segregation. In order to model solute drag effect, however, the GB region should be regarded as a physical entity with a finite width because the solute drag effect is a result from the diffusional interaction between solute atoms and GBs. A powerful tool where both the thermodynamic and kinetic effects of the GB segregation are treated in a unified way is the phase-field model. Until now several phase-field models for GB motion with segregation have been proposed [1-4]. In this study we show that all the phase-field models for GB segregation are implicitly assuming a two phase system where the GB is regarded as a single phase independent from the matrix grain phase and they implicitly adopt the equal composition condition [2-4] or the equal chemical potential condition [1] between two phases. The model combined with the equal composition condition between two phases and the ideal solution behavior of solute and solvent atoms has been most widely used for simulation of the solute drag effect in grain growth. However, we show that the equal composition condition in this model makes the GB energy change only within a very restricted range. For an example with the solute concentration of 1% at grain matrix and typical other physical parameters, the segregation can reduce the GB energy at most within 10 %. This problem which may severely restrict the applicability of the model to real systems can be completely eliminated by adopting the equal chemical potential condition, instead of the equal composition condition. Even though such a phase-field model [1] has been proposed, there has not been any application of the model to grain growth phenomena. We anticipate the phase field model adopting the equal chemical potential condition to play a central role in elucidating the grain growth behaviors with GB segregation.


[1] P.R. Cha, S.G. Kim, D.H. Yeon and J.K. Yoon, Acta Mater., 50 (2002) 3817

[2] K. Gronhagen and J. Agren, Acta Mater., 55 (2007) 955

[3] S.G. Kim and Y.B. Park, Acta Mater., 56 (2008) 3739

[4] F. Abdeljawad and S.M. Foiles, Acta Mater., (2015) in Press

 

Department of Materials Science and Engineering


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