Grain boundary enhanced ductility of ultrafine grained materials

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K04783
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 26050:Material processing and microstructure control-related
• Research Institution: Doshisha University
• Principal Investigator: Miyamoto Hiroyuki 同志社大学, 理工学部, 教授 (10298698)
• Co-Investigator(Kenkyū-buntansha): 湯浅 元仁 同志社大学, 理工学部, 准教授 (70635309)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 強ひずみ加工 / 超微細結晶材料 / ナノ結晶材料 / 強度 / 加工性

Outline of Final Research Achievements

Severe plastic deformation (SPD) can fabricate high-strength materials by forming ultrafine grained (UFG) microstructure. But, in general, as in other methods, strengthening accompanies ductility loss. Low ductility, which is usually evaluated by the uniaxial tensile tests, has been attributed to low strain hardening of UFG structure where dislocation slip and its accumulation is very limited. In the present work, it is shown that the compressive ductility, or classically called malleability of UFG materials can be comparable or potentially superior to that of coarse-grained counterparts in an appropriate stress state. The high malleability of UFG materials by SPD can be attributed to the unique deformation mechanism related with non-equilibrium grain boundaries and their high damage tolerance. The present results present a prospect for expanding industrial application of UFG materials, which has been limited because of low tensile ductility.

Free Research Field

金属材料工学

Academic Significance and Societal Importance of the Research Achievements

構造用金属材料の高強度化は構造物の軽量化の手段であり、省資源省エネルギーに寄与できる。高強度化の強化手法の一つである結晶粒微細化はその他の方法と比較して、希少金属が多い合金元素が不要であるため、今後は重要な方法となる。一方、通常は高強度化により延性が低下する。本研究では圧縮応力下での展性は通常粒径材と比較しても遜色ないことが明らかになった。このことは加工条件をうまく選択すれば、超微細結晶材料の二次加工性を引き出すことができることを示唆している。