Redefinition of states of short-range order (SRO) in alloys

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K18954
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 26:Materials engineering and related fields
• Research Institution: Kyushu University
• Principal Investigator: Hata Satoshi 九州大学, 総合理工学研究院, 教授 (60264107)
• Project Period (FY): 2018-06-29 – 2021-03-31
• Keywords: 短範囲規則 / 電子顕微鏡 / 逆位相境界 / 合金 / 規則ー不規則変態 / 三次元 / 準周期構造 / 副単位胞

Outline of Final Research Achievements

Local atomic arrangements of short-range order (SRO) in Ni4Mo alloy were investigated by aberration-corrected annular-dark-field scanning transmission electron microscopy. The SRO structure is a three-dimensional domain structure that consists of the two structural parts: (i) a common structural unit among several long-range ordered (LRO) structures of stable Ni4Mo or metastable Ni3Mo and Ni2Mo phases and (ii) an aperiodic and anisotropic arrangement of sub-unit-cells of these phases. In the course of SRO-LRO transition, the structural part (i) grows continuously, while the structural part (ii) stops its growth and, instead, preferential growth of the stable Ni4Mo sub-unit-cells into its LRO domains. Finally, a new definition of SRO based on anti-phase domain boundary energy was proposed.

Free Research Field

金属物性

Academic Significance and Societal Importance of the Research Achievements

短範囲規則（SRO）構造は、合金をはじめとする種々の結晶化合物で観察され、特にハイエントロピー合金や鉄鋼材料などでは力学特性に顕著な影響を及ぼす構造因子として今も研究がなされている。従来の規則ドメインサイズや原子相関距離に基づくSROの定義に比べると、本研究から導いた逆位相境界（APB）エネルギーに基づくSROの定義は、局所的な原子配列やAPB、すなわち結晶欠陥あるいは部分規則状態の構造的特徴を示すものである。この定義は、例えば、転位とSROの相互作用や逆位相ドメイン組織の生成過程など、材料物性や組織制御との関係を考える上で有効なSROの知見になるものと考えられる。