신소재공학과

Seminar

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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.


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Notice Special 11/14 (Wed) Prof. Hui-Ming Cheng (Director and Professor, Tsinghua University, IMR CAS) ADMINI 2018.11.13 14
Notice Special 11/20 (Tue) Prof. Alfonso H. W. Ngan (Department of Mechanical Engineering, University of Hong Kong) file ADMINI 2018.11.13 11
Notice Regular 11/13 (Tue) Dr. Kang-Wook Lee (SK Hynix) ADMINI 2018.11.13 10
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Notice Special 11/2 (Fri) Dr. Sungbong Park (Intel Corporation) ADMINI 2018.10.30 148
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261 Regular 5/8 (Tue) Prof. Ju-Young Kim (UNIST MSE) ADMINI 2018.05.09 702
» Regular 5/1 (Tue) Prof. Duk-Yong Yoon (KAIST MSE) ADMINI 2018.04.30 840
259 Regular 4/24 (Tue) Kyeong Ho Chang (CEO, Innox Advanced Materials) ADMINI 2018.04.23 730
258 Regular 4/10 (Tue) Prof. Ki Jun, Yu (Yonsei Univ., School of Electrical and Electronic Engineering) ADMINI 2018.04.09 804
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256 Regular 3/27 (Tue) Prof. Seungbum Hong (KAIST MSE) ADMINI 2018.03.26 642
255 Regular 3/20 (Tue) Prof. Jung In-Ho (Seoul National University, MSE) ADMINI 2018.03.20 541
254 Regular 3/13 (Tue) Prof. Jong-Beom Baek (School of Energy and Chemical Engineering, UNIST) ADMINI 2018.03.13 506
253 Regular 3/6 (Tue) Prof. Seok-Young Ryu (KAIST CS) ADMINI 2018.03.05 429
252 Regular 2/27 (Tue) Dr. Jin-Woo Han (NASA) ADMINI 2018.02.27 489
251 Special 2/20 (Tue) Dr. Jae Beom Jang (Sungkyunkwan Univ) ADMINI 2018.02.19 447
250 Special 2/8 (Thu) Prof. Pei-Chen Su (Nanyang Technological University) file ADMINI 2018.02.05 453
249 Special 2/13 (Tue) Prof. Sungkyu Kim (Northwestern Univ) ADMINI 2018.01.31 519
248 Special 1/9 (Tue) Dr. Choon Won Byeon, ETRI ADMINI 2018.01.09 522
247 12/23 (Sat) Prof. Liangbing (Bing) Hu/Univ. of Maryland file ADMINI 2017.12.22 540
246 Regular 11/28 (Tue) Dr. Woo-Jin Lee (Ministry of Science and ICT.) ADMINI 2017.11.24 1178
245 Special 11/24 (Fri) Takashi NOGUCH (University of the Ryukyus) ADMINI 2017.11.23 845
244 Special 11/21 (Tue) Dr. Young Ki Lee (ETRI) file ADMINI 2017.11.20 1027
243 Special 11/22 (Wed) Prof. Sung Hoon Kang (Johns Hopkins University) file ADMINI 2017.11.20 1259
242 Regular 11/21 (Tue) Dr. Byoung Koun Min, (KIST) ADMINI 2017.11.17 1408
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