신소재공학과

Seminar

Date 20180501 

MSE Regular Seminar



■ Title Principles of Chemically Induced Interface Migration and Abnormal Grain Growth


Speaker:  Prof. Duk-Yong Yoon (KAIST MSE)  

 

■ Date and Time :  5/1 (Tue) 16:00

 

■ Venue :  Applied Engineering Department (W1-1) Multimedia Lecture Hall (1st Floor)

 

 Abstract : 

In 1970s it was observed that grain boundaries and intergranular liquid films migrated when they came into contact with solute sources. Solute-rich alloys were produced behind the migrating interfaces.  Hillert proposed that the  solute atoms diffused ahead of the migrating interfaces producing coherency  strains that drove the migration. In this work solute atoms of large and small size  were used to vary the coherency strain from negative to positive values and when the estimated strain was 0, the interfaces did not migrate. This result was a definitive evidence for Hillert’s coherency strain theory and provides a foundation for a new perspective on solute diffusion process in polycrystalline systems .

      In some polycrystals the grains grow normally with a narrow size distribution which remains constant. Polycrystals sometimes show also abnormal grain growth  where only some grains grow to very large sizes while the others remain relatively small. In some alloys prepared by liquid phase sintering at low temperatures the grains are polyhedral with flat surfaces and grow abnormally. These flat surfaces are singular with the minimum surface energy with respect to the surface orientation. The singular surface moves forward by two dimensional nucleation of steps and hence the large grains grow much faster than the rest, resulting in abnormal growth. At high temperatures the grain surfaces undergo roughening transition and the grains become nearly spherical with atomically rough surface. The grains then grow normally.  The polycrystalline single phase alloys (without any liquid phase) also show the same roughening transition of grain boundaries with temperature increase and the change of grain growth from abnormal to normal. These results show that abnormal grain growth is caused by the nucleation and growth of steps on singular interfaces. In some materials  additives or change of atmosphere can also induce interface roughening and hence the change of grain growth behavior. His theory has been applied to the growth of large single crystals of various shapes and compositions from polycrystals.

No. Subject Author Date Views
Notice 7/25 (Wed) Dr. Chang Sub Kim (Department of MSE, MIT) ADMINI 2018.07.24 217
Notice 7/13 (Fri) Prof. Dong Ryeol Whang (Johannes Kepler University Linz, Austria) ADMINI 2018.07.09 219
Notice 6/5 (Tue) Prof. Sunghwan Lee (Baylor University) ADMINI 2018.06.05 428
263 5/29 (Tue) Prof. Sang Ho Oh (Yonsei Univ. College of Medicine) ADMINI 2018.05.29 431
262 5/15 (Tue) Prof. Myung Gil Kim (Dept. of Chemistry, Chung-Ang Univ.) ADMINI 2018.05.15 642
261 5/8 (Tue) Prof. Ju-Young Kim (UNIST MSE) ADMINI 2018.05.09 578
» 5/1 (Tue) Prof. Duk-Yong Yoon (KAIST MSE) ADMINI 2018.04.30 705
259 4/24 (Tue) Kyeong Ho Chang (CEO, Innox Advanced Materials) ADMINI 2018.04.23 609
258 4/10 (Tue) Prof. Ki Jun, Yu (Yonsei Univ., School of Electrical and Electronic Engineering) ADMINI 2018.04.09 700
257 4/3 (Tue) Master Byung-Gi Choi (Samsung Advanced Institute of Technology) ADMINI 2018.04.02 572
256 3/27 (Tue) Prof. Seungbum Hong (KAIST MSE) ADMINI 2018.03.26 543
255 3/20 (Tue) Prof. Jung In-Ho (Seoul National University, MSE) ADMINI 2018.03.20 416
254 3/13 (Tue) Prof. Jong-Beom Baek (School of Energy and Chemical Engineering, UNIST) ADMINI 2018.03.13 413
253 3/6 (Tue) Prof. Seok-Young Ryu (KAIST CS) ADMINI 2018.03.05 372
252 2/27 (Tue) Dr. Jin-Woo Han (NASA) ADMINI 2018.02.27 438
251 2/20 (Tue) Dr. Jae Beom Jang (Sungkyunkwan Univ) ADMINI 2018.02.19 408
250 2/8 (Thu) Prof. Pei-Chen Su (Nanyang Technological University) file ADMINI 2018.02.05 395
249 2/13 (Tue) Prof. Sungkyu Kim (Northwestern Univ) ADMINI 2018.01.31 478
248 1/9 (Tue) Dr. Choon Won Byeon, ETRI ADMINI 2018.01.09 495
247 12/23 (Sat) Prof. Liangbing (Bing) Hu/Univ. of Maryland file ADMINI 2017.12.22 515