取向MnCoSi基合金可逆巨磁致伸缩效应研究

MnCoSi alloy is a potential magnetostrictive material. Due to the rare tricritical behavior, reversible magnetostriction can be fulfilled during the magnetic field induced second-order transition. However, due to the high temperature of tricritical point and large critical field in MnCoSi alloy, the obtained room-temperature magnetostriction is generated from high field-induced first-order transition, which is accompanied by large irreversibility. Besides these, poor mechanical property and the difficulty to prepare textured samples also affect its further application as a magnetostrictive material. In order to overcome these hurdles, the current proposal intends to reduce the temperature of tricritical point and the critical field by designing composition. By this improvement, low field-induced second-order metamagnetic transition can be obtained at room temperature. Base on this, the current proposal will attempt to prepare textured and dense samples by improving the preparation method. With the existence of texture, enhanced magnetostriction can be achieved in MnCoSi-based bulk. The current proposal is aiming to design a transition metal-based alloy with giant reversible magnetostrictive effect under low field at room temperature. The implementation of this proposal is helpful to the application of MnCoSi-based alloys as a magnetostrictive material.

由于具有特殊的三相临界行为，MnCoSi基合金能够通过磁场诱导的二级相变实现可逆巨磁致伸缩效应，克服了一级相变磁致应变不可逆的缺陷，而且不含有稀缺的重稀土元素，具有重大研究价值。然而，正份MnCoSi合金难以取向、易碎，且磁致伸缩驱动场高、伸缩量有限，更关键的是由于三相点温度较高，磁致伸缩效应不可逆。针对这些缺陷，本项目拟基于合金成份设计，通过三相临界行为的调控，降低体系三相点温度及相变临界场，以获得室温、低场诱导的二级相变；并在此基础上，创新和改进取向制备技术，实现取向、致密MnCoSi基合金的制备，增大合金块体饱和磁致伸缩。最终，在取向且致密的MnCoSi基合金中，通过磁场诱导的二级相变，实现室温、低场、可逆的巨磁致伸缩效应。本项目的研究成果对于MnCoSi基合金在磁致伸缩领域的推广应用具有重要价值。

巨磁致伸缩材料在振动器、灵敏器件、声纳、能量转化等军、民用领域具有较大的应用价值。虽然多种巨磁致伸缩材料已被发现，但现有的材料存在包含重稀土元素以及磁致伸缩效应有限的不足。所以，基于新机制开发新型无稀土巨磁致伸缩材料具有重要意义。本项目基于MnCoSi合金特殊的三相临界行为，通过合理的调控，利用磁场诱导的二级相变，实现了室温、低场、可逆且较大的磁致伸缩效应。在优化后的合金中，室温相变临界磁场由原先的2.5 T降低至0.5 T，饱和磁致伸缩达到1000 ppm以上，效应媲美于Terfenol-D多晶。这大幅度增加了该类无稀土磁致伸缩材料的应用价值。本项目还基于调控结果，分析了合金相变临界磁场与Mn-Mn间距的联系，揭示了调控机理，给出了实现室温、低场且可逆磁致伸缩的可行方案；制备了织构化的MnCoSi合金，提升了合金的磁致伸缩效应，分析了织构形成的基本原因；通过磷以及过渡金属元素共掺，消灭了合金高温结构相变，在保证磁致相变存在的情况下，实现了合金致密无裂纹。总之，本项目系统地研究并调控了MnCoSi合金的三相临界行为，同时降低了合金的相变临界磁场及三相点温度，利用磁场诱导的二级相变，实现了室温、低场、可逆且较大的磁致伸缩效应，完成了预期研究目标。

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