Heusler合金NiCoMnIn的弹热效应与相变滞后调控研究

Elastocaloric cooling technique, originating from the stress-induced superelasticity, is energy-efficient and environmentally friendly. Adiabatic temperature change and transformation hysteresis are significant parameters in determining the cooling efficiency of elastocaloric materials.The competition between stress-driven martensitic transformation and stress-induced dislocation slip is inevitable in shape memory alloys, and both phenomena affect the magnitude of elastocaloric effect. In view of this, controlling the interaction of austenite-martensite interfaces with defects and enhancing the fraction of reversible transforming phase are essential to obtain materials with a combination of narrow hysteresis and large adiabatic temperature.Therefore, the current proposal will utilize Heusler-type NiCoMnIn alloy as a model system. In such a system, due to high composition sensitivity of magnetic entropy change, we will build relationships among composition, transformation temperatures and transformation entropy changes and obtain optimized alloy compositions with large latent heat. Furthermore, for this alloy system, both martensite variant and austenite modulus are sensitive to crystallographic orientation. By controlling the solidification conditions, we will obtain highly oriented single-phase alloys with low elastic modulus, with an aim to reduce the transformation hysteresis and enhance the reversibility of adiabatic temperature change. The purpose of this project is to reveal control mechanisms for elastocaloric effect and to explore room-temperature solid-state refrigeration materials with large and reversible adiabatic temperature change.

基于应力驱动超弹性的弹热制冷是高效、绿色的新型制冷方法，绝热温变和应力滞后是决定弹热材料制冷效率的重要参数。鉴于应力驱动相变和应力诱导滑移变形在影响弹热效应方面的竞争关系，控制奥氏体-马氏体相界面与缺陷交互作用、扩大可逆相的体积分数被认为是获得低相变滞后、大绝热温变的关键。为此，本项目拟以Heusler型NiCoMnIn合金为对象，利用磁熵变对成分的敏感性，构建成分、相变温度与相变熵变的关系，优化出具有大相变潜热的合金成分；在此基础上，基于应力作用下奥氏体-马氏体变体转变和奥氏体弹性模量对晶体取向的敏感性，通过控制凝固条件获得高取向、低弹性模量的单相奥氏体合金，以达到降低相变滞后，进而提高绝热温变可逆性的目的。研究工作对于揭示弹热效应的控制机理、开发兼具低滞后和大循环绝热温变的室温固态制冷材料具有重要的意义。

绝热温变和应力滞后是决定形状记忆合金弹热材料制冷效率的重要参数。强一级相变特征的形状记忆合金具有双重效应：在带来巨热效应的同时，伴随着滞后现象的存在，使得加、去外场循环过程中系统耗散额外的能量，制冷材料绝热温变出现衰减，进而导致制冷系统的效率降低。为此，控制一级相变材料的应力滞后是实现大且可逆、稳定弹热温变的关键。本项目以Heusler型NiCoMnIn合金为对象，探索了合金成分、相变温度与相变潜热的关系，构建了合金凝固条件、晶体取向与超弹性相变特征参数间的关联，揭示了合金晶体取向特征对准绝热条件下滞后能量损耗、材料制冷性能系数的影响。发现择优晶体取向为[100]A 和[311]A的合金在6%的大施加应变条件下呈现极窄的等温应力滞后（Δσhys= 34 MPa）。合金的晶体取向特征显著地影响准绝热弹性制冷对应的应力-应变响应，不同晶体取向特征所导致的卸载阶段材料制冷性能系数的变化可达2.6倍。这些研究工作对于揭示弹热效应的控制机理、设计兼具低滞后和大循环绝热温变的室温固态制冷材料具有重要的意义。