10/16 Seminar Speech

SpeakerProf. Nobuhiro Tsuji

OrganizationDepartment of Materials Science and Engineering, Kyoto University

TopicPossibilities of Bulk Nanostructured Metals as Advanced Structural Material

Date10:10 , 2017.10.16

LocationRoom 101, Liberal Education Classroom Building

Education

1989.3 Bachelor, Dept. Mater. Sci. Tech., Faculty of Eng., Kyoto Univ., Japan
1991.3 Master, Dept. Mater. Sci. Tech., Graduate School of Eng., Kyoto Univ., Japan.
1994.3 PhD, Dept. Mater. Sci. Tech., Graduate School of Eng., Kyoto Univ., Japan.

Professional Experience

1993.4-1994.3 JSPS (Japan Soc. For Promotion of Science) Research Fellow (DC)
1994.4-2000.3 Assistant Professor, Dept. Mater. Sci. Eng., Osaka Univ., Japan
2000.4-2009.2 Associate Professor, Dept. Adaptive Machine Systems, Osaka Univ., Japan.
2009.3-present Professor, Dept. Materials Science & Eng., Kyoto Univ., Japan
1998.7-1999.7 Visiting Scholar, Colorado School of Mines, USA (JSPS Research Fellow Abroad)
2001.4-2001.9 Part-time Lecturer, Tokyo Institute of Technology, Japan.
2003.7-2003.8 Visiting Professor, Risø National Laboratory, Denmark.
2004.12-2005.3 Part-time Lecturer, Toyohashi University of Technology, Japan.
2006.12-2007.1 Visiting Professor, Risø National Laboratory, Denmark.
2007.4-2007.9 Part-Time Lecturer, Gifu University, Japan.
2011.4-2011.9 Invited Professor, Institute of Materials Research (IMR), Tohoku University
2013.4, 2014.10, 2015.10, 2016.12, 2017.12
Visiting Professor, Dept. of Materials Science and Engineering, Indian Institute of Technology, Hyderabad
2015.4-2016.3 Invited Professor, Joining and Welding and Research Institute (JWRI), Osaka University
2015.10- Visiting Professor, International Research Center on Giant Straining for Advanced Materials, Kyushu University

Abstract

Bulk nanostructured metals (or ultrafine grained (UFG) metallic materials), of which mean grain size of the matrix is smaller than 1 um, usually perform surprisingly high strength, high fatigue strength and good low-temperature toughness, but their tensile ductility, especially uniform elongation, is limited in many cases. This is attributed to the early plastic instability caused by high flow stress and limited strain-hardening capability of the UFG materials [1]. Therefore, an important strategy for managing both strength and ductility in nanostructured metals is to increase the strain-hardening capability by controlling microstructures, such as, dispersing nano-particles in the UFG matrix, making the nanostructure multi-phased, etc. [2]. Nanostructures fabricated by severe plastic deformation (SPD) naturally have characteristics of deformation structures. This is one of the main microstructural reasons of limited ductility, as strain-hardened metals usually do not show large tensile elongation. In order to remove the deformed characteristics, annealing processes are usually applied. But in many cases of the SPD processed materials, the mean grain size becomes over 1 um after fully annealed microstructures are obtained, so that the strength decreases very much. Recently, on the other hand, we have succeeded in obtaining fully-annealed nanostructures in some alloys [3-7]. The materials show both high strength and enough strain-hardening ability to result in large uniform elongation. All these ways to manage strength and ductility will be presented in the seminar.

References:
[1] N.Tsuji, Y.Ito, Y.Saito and Y.Minamino: Scripta Mater., Vol.45, No.12 (2002), pp.893-899.
[2] N.Tsuji, N.Kamikawa, R.Ueji, N.Takata, H.Koyama and D.Terada: ISIJ International, Vol.48, No.8 (2008), pp.1114-1121.
[3] R.Saha, R.Ueji and N.Tsuji: Scripta Mater., Vol.68, Issue 10 (2013), pp.813-816.
[4] Y.Z. Tian, L.J. Zhao, S. Chen, A. Shibata, Z.F. Zhang, N. Tsuji: Scientific Reports, Vol.5 (2015), 16707.
[5] R.Zheng, T.Bhattacharjee, A.Shibata, T.Sasaki, K.Hono, M.Joshi and N.Tsuji: Scripta Mater., 131 (2017), pp.1-5.
[6] S.Yoshida, T.Bhattacharjee, Y.Bai and N.Tsuji: Scripta Mater., 134 (2017), pp.33-36.
[7] Y.Z.Tian, S.Gao, L.J.Zhao, S.Lu, Z.F.Zhang and N.Tsuji: Scripta Mater., 142 (2018), pp.88-91.