Ni-Mn基Heusler合金的显微结构调控及性能研究

Study on Microstructure Regulation and Properties of Ni-Mn-Based Heusler Alloys

摘要: Ni-Mn基Heusler合金因其磁–结构相变特性表现出多种功能特性，如磁热效应、磁阻效应与磁场诱导形状记忆效应等，受到广泛关注。本文针对其中的Ni-Mn-In合金展开研究，利用定向凝固技术，制备得到了具有强织构的样品，并利用扫描电子显微镜、X射线衍射仪、差热扫描量热仪等仪器，对样品的显微结构、相变行为以及性能变化进行了深入研究。研究表明，在室温下样品为L2₁立方奥氏体，且定向凝固后得到了织构。通过对喷铸与定向凝固样品的相变行为进行分析，发现定向凝固后相变温度显著上升(从约170 K升高至约200 K)，居里温度则基本保持不变。同时，定向凝固样品的相变宽度更窄，即相变更剧烈，相变的热滞后行为也得到显著改善(从19.8 K降低至12.5 K)。此外，对定向凝固样品的热膨胀性能进行了测试：在升温奥氏体相变过程(215~230 K)中，沿生长方向(LD)发现了显著的负热膨胀现象，热膨胀系数α_L = −259.6 ppm/K，而垂直于生长方向(ND)则呈现正热膨胀行为，热膨胀系数高达452.7 ppm/K，远高于喷铸样品的173.9 ppm/K。综上所述，定向凝固方法对Ni-Mn-In合金的相变行为起到显著调控作用，并成功在该体系合金中获得了负热膨胀性能。

Abstract: Ni-Mn-based Heusler alloys have attracted widespread attention due to their magnetic-structural phase transition characteristics, which exhibit various functional properties such as the magnetocaloric effect, magnetoresistance, and magnetic-field-induced shape memory effect. This paper focuses on the Ni-Mn-In alloy, where directional solidification technology was used to prepare samples with strong texture. The microstructure, phase transition behavior, and performance changes of the samples were thoroughly studied using instruments such as scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry. The research shows that at room temperature, the sample is in the L2₁ cubic austenite phase, and after directional solidification, a texture is obtained. By analyzing the phase transition behavior of both spray-cast and directionally solidified samples, it was found that the phase transition temperature significantly increases after directional solidification (rising from approximately 170 K to around 200 K), while the Curie temperature remains nearly unchanged. Meanwhile, the phase transition width of the directionally solidified sample is narrower, indicating a more abrupt transition, and the thermal hysteresis behavior of the phase transition is also significantly improved (reduced from 19.8 K to 12.5 K). Additionally, the thermal expansion properties of the directionally solidified samples were tested: during the austenitic phase transition process (215~230 K) upon heating, a significant negative thermal expansion phenomenon was observed along the growth direction (LD), with a thermal expansion coefficient of α_L = −259.6 ppm/K, whereas perpendicular to the growth direction (ND), positive thermal expansion behavior was exhibited, with a thermal expansion coefficient as high as 452.7 ppm/K, which is much higher than the 173.9 ppm/K of the spray-cast sample. In conclusion, the directional solidification method plays a significant role in modulating the phase transition behavior of Ni-Mn-In alloys and, for the first time, negative thermal expansion properties were obtained in this alloy system.