Projects

Grant-in-Aid for Scientific Research (S)

Breakthrough toward “second-generation” grain boundary engineering
Head of laboratory Sadahiro Tsurekawa( Kumamoto University, Faculty of Advanced Science and Technology, Professor )
Collaborative researchers 大村 孝仁(国立研究開発法人物質・材料研究機構 構造材料研究拠点・副拠点長)
小林 重昭(足利工業大学工学部・准教授)
Dr. Seiichiro II (National Institute for Materials Science)
連携研究者 森園 靖浩(熊本大学大学院先端科学研究部・准教授)
研究協力者 山室 賢輝(熊本大学工学部技術部・技術専門職員)
Pavel Lejček(チェコ科学アカデミー物理研究所・教授)
Dmitri A. Molodov(アーヘン工科大学・教授)
Term of project Academic years 2016-2020 (April 2016 - March 2021)

Purpose and Background of the Research

Fig.1 Effect of grain boundary control on corrosion in austenitic stainless steel (SUS304): (a) Conventionally processed, (b) grain boundary engineered. (S.Tsurekawa et al., Acta Mater., 54,3617, (2006).)
Fig.1 Effect of grain boundary control on corrosion in austenitic stainless steel (SUS304): (a) Conventionally processed, (b) grain boundary engineered. (S.Tsurekawa et al., Acta Mater., 54,3617, (2006).)

Bulk properties of polycrystalline materials are significantly affected by grain boundaries. Tadao Watanabe has proposed the concept of grain boundary engineering for providing desirable properties of polycrystalline materials” in 1983 / 1984 on the basis of the structure-dependent grain boundary properties, which is nowadays known to be useful for achieving enhanced bulk properties like creep resistance and corrosion resistance (Fig. 1). As mentioned above, “first generation” grain boundary engineering achieved certain results. However, there still remain some issues to be settled for further establishment of grain boundary engineering: e.g., grain boundary engineering is not commonly applied to the materials with a high stacking fault energy.

Motivation of this project is to achieve a breakthrough toward “second generation” grain boundary engineering. We will deal with two major issues as follows:

Issue 1: Comprehensive understanding of grain boundary phenomena to strengthen fundamental base of grain boundary engineering

  • Local mechanical properties near the grain boundary – Understanding Hall-Petch relation on the basis of the interaction between grain boundary and dislocations.
  • Structure and properties of grain boundaries.

Issue 2: Guiding principle for grain boundary control of materials with high stacking fault energy

Research Methods

(1) Orientation controlled bicrystals are used for nanoindentation tests to study the local mechanical properties near the grain boundaries, and for in-situ deformation / observation in TEM to examine the relation between the dislocation motion and mechanical response.
 (2) Quantitative evaluation of grain boundary microstructure using the fractal and percolation theory.

Expected Research Achievements and Scientific Significance

The achievements of this study make it possible to apply the grain boundary engineering to a wide-rang of materials, and would promote an innovation for development of new advanced materials based on grain boundary functions. In addition, we propose a new elements strategy because grain boundary engineering can achieve enhanced properties even for conventional materials without using further allying elements.

Publications Relevant to the Project

  • T. Watanabe, S. Tsurekawa, The Control of Brittleness and Development of Desirable Mechanical Properties in Polycrystalline Systems by Grain Boundary Engineering, Acta Mater., 47, 4171-4185, 1999.
  • S. Tsurekawa, Y. Chihara, K. Tashima, P. Lejček, Local plastic deformation in the vicinity of grain boundaries in Fe-3 mass% Si alloy bicrystals and tricrystal, J. Mater. Sci., 49, 4698 - 4704, 2014.