Tohoku University · 재료과학
오모리 히로히로 교수의 연구실은 주로 철기반 형상 기억 합금과 초탄성 합금의 물성 및 미세구조 제어를 핵심으로 하며, 온도에 따른 임계 응력 변화를 최소화하거나 제어할 수 있는 신소재 개발에 초점을 맞추고 있습니다. 특히 자기적 기여로 인한 엔트로피 변화를 조절하여 초탄성 응력의 온도 의존성을 낮추거나 반전시키는 데 성공했으며, 고온에서의 안정성과 큰 초탄성 변형률을 동시에 확보하는 데 기여하고 있습니다. 또한, 단일결정 및 대결정성 구조의 형성 기법 개발을 통해 합금의 기계적·자기적 성능을 극대화하는 데에도 기여하고 있습니다.
표시된 성과는 수집된 데이터 기준으로 산출되며, 일부 차이가 있을 수 있습니다.
In superelastic alloys, large deformation can revert to a memorized shape after removing the stress. However, the stress increases with increasing temperature, which limits the practical use over a wide temperature range. Polycrystalline Fe-Mn-Al-Ni shape memory alloys show a small temperature dependence of the superelastic stress because of a small transformation entropy change brought about by a magnetic contribution to the Gibbs energies. For one alloy composition, the superelastic stress var
In polycrystalline materials, grain growth occurs at elevated temperatures to reduce the total area of grain boundaries with high energy. The grain growth rate usually slows down with annealing time, making it hard to obtain grains larger than a millimeter in size. We report a crystal growth method that employs only a cyclic heat treatment to obtain a single crystal of more than several centimeters in a copper-based shape-memory alloy. This abnormal grain growth phenomenon results from the forma
Shape memory alloys recover their original shape after deformation, making them useful for a variety of specialized applications. Superelastic behavior begins at the critical stress, which tends to increase with increasing temperature for metal shape memory alloys. Temperature dependence is a common feature that often restricts the use of metal shape memory alloys in applications. We discovered an iron-based superelastic alloy system in which the critical stress can be optimized. Our Fe-Mn-Al-Cr
Martensitic and magnetic properties of Fe–Mn–Ga single and polycrystalline alloys were investigated. It was found that Fe–Mn–Ga alloys exhibit martensitic transformation from the paramagnetic L21 Heusler parent phase to the ferromagnetic L10 martensite phase. The martensitic transformation temperatures increased by about 20 K by the application of a magnetic field of 7 T, and a metamagnetic phase transition was observed. In addition, a magnetic field-induced strain of 0.6% associated with magnet
Effects of grain size on superelastic properties in Fe-34Mn-15Al-7.5Ni alloy wires with a ⟨110⟩ fiber-texture were investigated by cyclic tensile tests. It was confirmed that the critical stress for induced martensitic transformation and the superelastic strain are functions of relative grain size d/D (d: mean grain diameter, D: wire diameter), and that the critical stress is proportional to (1–d/D)2 as well as in Cu-based shape memory alloys. A large superelastic strain of about 5% was obtained
Microstructure and martensitic transformation yielding a magnetic change were investigated for Fe43.5Mn34Al15Ni7.5 alloy with B2-type fine precipitates. Thermoelastic martensitic transformation from the ferromagnetic parent phase to the weak magnetic martensite with a nano-twinned fcc structure was confirmed. High-angle annular dark-field scanning transmission electron microscopic observation revealed that a β particle of about 10 nm maintains coherency with the matrix martensite phase, even tho
