主题：Stacking fault energy: a metallurgist's measure of the deformation mechanism

报告人：Prof. Se Kyun Kwon

时间：2017年6月16日（周五） 8:30-10:00

地点：李薰楼468室

报告摘要：

Plastic deformation mechanisms govern the mechanical properties of materials. In the face-centered cubic structuresuch as austenitic steels,dislocation glide is usually the major deformation mode and ε-martensite formation/twinning is activated as a secondary deformation mechanism. At the first stage of plasticdeformation, an intrinsic stacking fault is generated by a leading partial dislocation. The formation energy of such a planar fault is defined as the stacking fault energy (SFE). The stacking fault will successively evolve to full-slip or micro-twinning by a trailing partial or a twinning partial dislocation depending upon materials and applied stress condition.It has long been recognized that the SFE determines the deformation mechanism; as the SFE increases, the deformation mechanism changes from ε-martensite + dislocation glide to twinning + dislocation glide and finally  to dislocation glide-only. Therefore, it is important to know the size of the SFE in order to understand the deformation mechanism of a material. In this talk, we disclose the physical terms behindthe volumetric model of the SFE proposed by Olson-Cohen and the deformation-mode boundary of ε-martensite and mechanical twinning.

主讲人简介：

KWON, Se Kyun is an associate professor in Alternative Technology Laboratory, Graduate Institute of Ferrous Technology, Pohang University of Science and Technology. He got his B.S., M.S. and Ph.D. in POSTECH (advisor: Prof. B.I. Min) and worked as a research fellow in Uppsala University(2003-2005) and NIMS (2002-2003).His current research focuses on the theory and methodology of first principles theory and its applications to material systems mainly including strongly correlated electron systems, spintronics,metallic systems, High-Mn steels and Electrical Steels.His work has been published on PNAS, Acta Mater, PRL, PRB, etc.

Selective Publications
[1] M. Jo, Y.M. Koo, B.-J. Lee, B. Johansson, L. Vitos, and S.K. Kwon, Theory for Plasticity of Face-centered Cubic Metals,PNAS111, 6560 (2014).
[2] J.S. Jeong, W. Woo, K.H. Oh, S.K. Kwon, and Y.M. Koo, In situ Neutron Diffraction Study of the Microctructure and Tensile Deformation Behavior in Al-added High Manganese Austenitic Steels. Acta Mater.60, 2290 (2012).
[3] S.S. Baik, S.K. Kwon, and B.I. Min, Optimization of Magnetic Flux Density in Electrical Steels: Slater-Pauling Pattern Repetition in Multicomponent Alloys. Phys. Rev. B85, 052402 (2012).
[4] M.P.J. Punkkinen, S.K. Kwon, J. Kollar, B. Johansson, and L. Vitos, Compressive Surface Stress in Magnetic Transition Metals. Phys. Rev. Lett106, 057202 (2011).
[5] S.K. Kwon, Z. Nabi, K. Kádas, L. Vitos, J. Kollár, B. Johansson, and R. Ahuja. Surface energy and stress release by layer relaxation. Phys. Rev. B72, 235423 (2005).
[6] S.K. Kwon and B.I. Min. Origin of the giant magnetic moments of Fe imputiries on and in Cs films.Phys. Rev. Lett.84, 3970 (2000).