Effect of Grain Boundary Energy on Surface-Energy Induced Abnormal Grain Growth in Columnar-Grained Film

Jung, Jung-Kyu,Hwang, Nong-Moon,Park, Young-Joon,Joo, Young-Chang 대한금속학회 2002 METALS AND MATERIALS International Vol.8 No.1

In columnar-grained film with anisotropy in the surface energy, abnormal grain growth occurs to minimize the overall energy. We studied the effect of grain boundary energy on the surface-energy driven abnormal grain growth in thin films using the Monte Carlo computer simulation. Our simulation results show that the growth speed of abnormal growth slows down when grain boundary energy increases. It is because the speed of normal growth driven by the grain boundary energy minimization gets faster with increasing grain boundary energy, while that of the abnormal growth induced by the fixed surface energy is consistent. The growth kinetics was monitored based on the growth velocity of the abnormal grains relative to the average growth velocity of all the grains. It was also found that the abnormal growth kinetics was retarded by impingements among abnormally growing grains when there was more than one abnormal grain.

Estimation of the Effect of Grain Boundary Diffusion on Microstructure Development in Magnetite Bi-crystal under Oxygen Chemical Potential Gradient at 823 K

Mitsutoshi Ueda,Toshio Maruyama 한국세라믹학회 2012 한국세라믹학회지 Vol.49 No.1

Mass transport near grain boundary in a magnetite bi-crystal has been estimated at 823 K by finite element method. Mass transport near grain boundary strongly depends on the diffusivities along grain boundary. If grain boundary diffusion has the same oxygen activity dependence as lattice diffusion, there is no mass transport between grains and grain boundary. On the other hand, mass transport between grains and grain boundary is observed in the case that grain boundary diffusion has different oxygen activity dependence.

Estimation of the Effect of Grain Boundary Diffusion on Microstructure Development in Magnetite Bi-crystal under Oxygen Chemical Potential Gradient at 823 K

Ueda, Mitsutoshi,Maruyama, Toshio The Korean Ceramic Society 2012 한국세라믹학회지 Vol.49 No.1

Mass transport near grain boundary in a magnetite bi-crystal has been estimated at 823 K by finite element method. Mass transport near grain boundary strongly depends on the diffusivities along grain boundary. If grain boundary diffusion has the same oxygen activity dependence as lattice diffusion, there is no mass transport between grains and grain boundary. On the other hand, mass transport between grains and grain boundary is observed in the case that grain boundary diffusion has different oxygen activity dependence.

Electrochemical micro-couple mechanism based on Si and Mn segregations revealing the initiation of grain boundary dissolution for Q235 carbon steel

Yong Zhou,Fuan Yan 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.120 No.-

The purpose of this work was to reveal the initiation mechanism of grain boundary dissolution (GBD) forcarbon steels in acidic electrolytes containing NO2 – . For Q235 carbon steel in a HNO3-NaNO2 solution withpH 4, the electrochemical methods of potentiodynamic polarization and scanning Kelvin probe forcemicroscope (SKPFM) were applied to explore electrochemical behavior, and the surface methods of scanningelectron microscope (SEM), electron back-scatter diffraction (EBSD) and scanning tunneling microscope(STM) were applied to explore surface microstructure and composition. Q235 carbon steelpresented the electrochemical behavior of activation-passivation-transpassivation in pH 4 HNO3-NaNO2 solution, GBD occurred on steel surface during anodic polarization. GBD initiation, which showeda selective characteristic, was found at the grain boundaries of relatively high Si and Mn contents (highSi-Mn grain boundary) when Q235 carbon steel was polarized to active–passive transition potential. Thegrain boundary segregations of Si and Mn played a critical role in the initiation of GBD, and an electrochemicalmicro-couple (EMC) mechanism based on the Si and Mn segregations was proposed to revealGBD initiation. EMC potential difference between high Si-Mn grain boundary and grain interior wasgreater than that between low Si-Mn grain boundary and grain interior, resulting in that GBD initiatedat high Si-Mn grain boundary. The detailed EMC mechanism of GBD initiation was discussed in this work.

이방성 결정립 계면에너지의 2차원 결정립 성장에 미치는 효과에 대한 컴퓨터 모사

김신우,Kim, Shin-Woo 한국결정성장학회 2012 韓國結晶成長學會誌 Vol.22 No.4

결정립 성장은 여러 가지 재료의 성질에 미치는 큰 영향으로 재료공학에서 매우 중요하다. 그래서 본 연구에서는 PC에서 대규모 상장 모델을 사용하여 이방성 결정립 계면에너지의 2차원 결정립 성장에 미치는 효과를 조사하였다. 컴퓨터 모사에서는 $2000{\times}2000$의 그리드 시스템과 약 7300개의 초기 결정립 개수가 사용되었다. 결정립계 에너지의 이방성의 비, ${\sigma}_{max}/{\sigma}_{min}$는 1부터 3까지 변경되었다. 이방성이 증가함에 따라 결정립 성장 지수, n은 2.05에서 2.37로 증가하였다. 결정립 크기의 분포는 등방성인 경우에는 중앙에 평탄한 영역을 보였으나 이방성의 경우에는 중앙의 평탄한 영역이 사라지고 매우 느리게 사라지는 작은 결정립에 기인하여 작은 결정립 크기의 분포가 약간 증가하였다. 마지막으로 모사된 결정립 미세구조가 이방성에 따라 비교, 분석되었다. The grain growth is very important because of its great influence on the various materials properties. Therefore, in this study, the effects of anisotropic grain boundary energy on grain growth in 2-D have been investigated with a large scale phase field simulation model on PC. A $2000{\times}2000$ grid system and the initial number of grains of about 73,000 were used in the computer simulation. The anisotropic ratio of grain boundary energy, ${\sigma}_{max}/{\sigma}_{min}$, has been varied from 1 to 3. As the anisotropy increased, the grain growth exponent, n, increased from 2.05 to 2.37. The grain size distribution showed a central plateau in the isotropic case, and was changed into no central plateau and the increasing population of very small grains in the anisotropic case, resulting from slowly disappearing grains. Finally, simulated microstructures were compared according to anisotropy.

Grain boundary engineering approach to improve hydrogen embrittlement resistance in FeMnC TWIP steel

Kwon, Young Jin,Jung, Seung-Pill,Lee, Byeong-Joo,Lee, Chong Soo Elsevier 2018 International journal of hydrogen energy Vol.43 No.21

<P><B>Abstract</B></P> <P>This investigation aimed to improve hydrogen embrittlement (HE) resistance of Fe17Mn−0.8C (wt %) TWIP steels by use of grain boundary engineering approach. The degree of enhancement in HE resistance by grain boundary engineering was compared with those of Al-added TWIP steels (Fe17Mn−0.8C1Al and Fe17Mn−0.8C2Al). By applying grain boundary engineering, the special boundaries that shared a high fraction of lattice points between neighboring grains were increased from 48% to 59%, and the morphology of grain boundaries was changed to ragged type. After hydrogen charging, fracture strength and reduction of area were clearly degraded in all four samples (Base, GBE, 1Al, and 2Al), revealing a transition of fracture mode from dimple fracture to intergranular fracture. However, the alloy with higher fraction of special boundaries had higher resistance to hydrogen-induced intergranular embrittlement. The HE resistance of GBE was obviously improved to a level similar to that of Al-added TWIP steels. Important implication of this work is that HE resistance can be greatly enhanced by controlling the distributions of grain boundary characters (GBCs) without adding Al. This was attributed to not only the higher fraction of special boundaries, but also the loss of continuity of random boundaries.</P> <P><B>Highlights</B></P> <P> <UL> <LI> HE resistance of FeMnC TWIP steel was enhanced by applying grain boundary engineering. </LI> <LI> The beneficial role of special boundaries to HE was quantitatively investigated. </LI> <LI> HE resistance of FeMnC TWIP steel can be greatly improved without Al addition. </LI> </UL> </P>

Grain-boundary plane orientation dependence of electrical barriers at Σ5 boundaries in SrTiO₃

Lee, S.B.,Lee, J.H.,Cho, Y.H.,Kim, D.Y.,Sigle, W.,Phillipp, F.,van Aken, P.A. Elsevier Science 2008 ACTA MATERIALIA Vol.56 No.18

Dependence of the electrical properties on grain-boundary plane orientation is examined by a combination of high-resolution transmission electron microscopy, impedance spectroscopy, and electron energy-loss spectrometry using two kinds of SrTiO<SUB>3</SUB> Σ5 ([100]/36.8<SUP>o</SUP>) bicrystalline grain boundaries: symmetric (310) (18.4<SUP>o</SUP>/18.4<SUP>o</SUP>) and asymmetric (8.4<SUP>o</SUP>/28.4<SUP>o</SUP>). While the symmetric grain boundary is observed to be straight with the symmetric (310)//(310) plane orientation, the asymmetric grain boundary is faceted into symmetric (310)//(310) and (210)//(210), and asymmetric (100)//(430). Grain-boundary impedance is observed only in the asymmetric grain boundary, and the electron energy-loss spectrometry quantification indicates that the asymmetric (100)//(430) facets are more oxygen-deficient than the symmetric ones. The results suggest that the asymmetric (100)//(430) facets are the most resistive among the three different facets.

Comparison of three-dimensional morphologies of abnormally growing grains between Monte Carlo simulations and experiments of Fe-3% Si steel

Na, Tae-Wook,Cho, Da-Hee,Park, Chang-Soo,Park, Jong-Tae,Han, Heung Nam,Hwang, Nong-Moon Elsevier 2018 Materials characterization Vol.144 No.-

<P><B>Abstract</B></P> <P>Three-dimensional (3-D) Monte Carlo simulations of grain growth with sub-boundaries in the presence of precipitates were performed based on the distribution of realistic grain boundary energy data. The simulated grains with sub-boundaries grew abnormally. The simulated and experimental morphologies of the abnormally growing grains in Fe-3%Si steel were compared. The experimental 3-D morphology was reconstructed from serially sectioned images. Both the simulated and experimental 3-D morphologies of abnormally growing grains have highly irregular and complicated shapes whereas both the simulated and experimental 3-D morphologies of normally growing grains have relatively regular and simple shapes. Growth by wetting is responsible for the highly irregular shape of the experimental abnormally growing grains of Fe-3%Si steel as well as for the highly irregular shape of the simulated abnormally growing grains.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Grains with sub-boundaries grew abnormally in the MC simulation with realistic grain boundary energy. </LI> <LI> The experimental 3-D morphology of Goss grain was reconstructed from serially sectioned images. </LI> <LI> 2-D sectioned microstructures of the MC simulation and experiment have highly irregular shape. </LI> <LI> Both simulated and experimental 3-D morphologies of AGG have similar complicated shapes. </LI> </UL> </P>

Abnormal grain growth induced by grain boundary segregation of yttrium in grain-oriented Fe-3%Si steel

Park, Hyung-Ki,Han, Chan-Hee,Park, Chang-Soo,Park, Jong-Tae,Joo, Hyung-Don Elsevier 2018 Materials characterization Vol.146 No.-

<P><B>Abstract</B></P> <P>The possibility of abnormal grain growth in grain-oriented Fe-3%Si steel by grain boundary segregation was investigated. Yttrium was selected to inhibit normal grain growth because its segregation at grain boundaries would efficiently reduce the grain boundary energy of iron, decreasing the driving force for grain growth. After secondary recrystallization, abnormal grain growth was successfully achieved without any precipitates. Observations by the Laue diffraction method confirmed that the abnormally grown grains had the Goss orientation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The abnormal grain growth in Fe-3%Si was induced without precipitates by alloying of yttrium. </LI> <LI> Grains grew abnormally to sizes exceeding 10 mm after secondary recrystallization. </LI> <LI> Observations by the Laue diffraction method confirmed that the abnormally grown grains had the Goss orientation. </LI> </UL> </P>

Misorientation Characteristics at the Growth Front of Abnormally-Growing Goss Grains in Fe–3%Si Steel

Tae‑Young Kim,Tae‑Wook Na,Hyung‑Seok Shim,Yong‑Keun Ahn,Yong‑Kwon Jeong,Heung Nam Han,Nong‑Moon Hwang 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12

Penetrating morphologies at the growth front of abnormally-growing Goss grains in Fe–3%Si steel was examined in view ofthe possibility that they are the two-dimensional section of the solid-state wetting (SSW) along the triple junction line. Toobtain the statistically meaningful data, 102 penetrated grain and 204 penetrating abnormally-growing Goss grain morphologieswere examined. The misorientation angles of penetrating and penetrated grains were measured by electron backscattereddiffraction. Among the 102 examined penetrated grain boundaries, none has low misorientation angles less than 15°,whereas 17.2% of the 204 penetrating grain boundaries have low misorientation angles, and 23.5% of them have coincidencesite lattice boundaries. Besides, boundary energies of penetrating Goss grains, which were estimated from misorientationangles of the three grains in the penetrating morphology, satisfied the energetic condition for SSW along the triple junctionline. These results imply that the abnormal grain growth of Goss grains in Fe–3%Si steel occurs by the mechanism of subboundaryenhanced SSW.