快速定向凝固新型铁基巨磁致伸缩合金晶体的制备及性能研究

Magnetostrictive alloys possess important potential applications in aeronautics and astronautics, energy safety and national defense, etc. The rare earth giant magnetostrictive alloys exhibit magnetostriction up to 1800 ppm. But due to the content of rare earth over 60%, the rare earth giant magnetostrictive alloys are too expensive to be used. The recently reported low-cost rare-earth-free FeGa magnetostrictive alloys exhibit the magnetostriction of just 300 ppm. The improvement of the magnetostriction of rare-earth-free (or slight amount of rare earth) magnetostrictive alloys encounters theoretical and technical bottlenecks.. . More recently, we have found that the magnetostriction of FeGa alloys could be improved up to 1900 ppm by the adding slight amount of strong magnetocrystalline anisotropic rare earth elements and by achieving non-equilibrium microstructure with supersaturation of rare earth elements through melt spinning technique. Therefore, the slightly rare earth doped FeGa alloys are expected as advanced iron-based giant magnetostrictive alloys. However, the miecroscopic mechanism of the enhancement of the magnetostriction caused by the slight addition of rare elements keeps unclear. One the orther hand, only two-dimensional ribbons can be produced by the melt spinning technique, with low degree of preferential orientation. In order to obtain three-dimensional crystals of the advanced iron-based giant magnetostrictive alloys, it is required to simultaneously realize the super saturation of rare earth elements and the crystal growth along the direction of the optimal magnetostrictive properties. So, the development of rapid directional solidification (Rapid DS) is of crucial importance.. . This project mainly investigates the rapid directional solidification technique and the control of metastable phase, preferential orientation and microstructure of advanced magnetoelastic materials. The solidification behavior of advanced magnetoelastic materials in the conditions of rapid directional solidification would be revealed. The formation of metastable phase, preferential orientation and the evolution of microstructure, and the corresponding mechanism, would be classified. The microscopic mechanis of the enhancement of the magnetostriction caused by the slight addition of rare elements would be clarified. Then advanced magnetoelastic metallic crystals with large magnetostrain properties would be prepared. Rapid directional solidification technique and theories would be developed.

磁致伸缩合金在航空航天、石油增采和国防建设等领域有重要应用前景。稀土巨磁致伸缩合金性能高（1800ppm），但稀土含量逾60%，成本极高，应用受限。近期报道低成本非稀土FeGa合金性能约300ppm。非稀土（少稀土）磁致伸缩合金高性能化遭遇原理和方法瓶颈。. 我们前期探索发现，在FeGa中添加微量（≤0.2%）强磁晶各向异性稀土元素，并通过快速凝固甩带获得过饱和固溶非平衡组织，性能高达1900ppm，有望成为新型铁基巨磁致伸缩合金。但快速凝固甩带仅获得二维薄带，且择优取向度低。高性能三维晶体制备需同步实现稀土过饱和固溶和沿性能最优方向生长，发展快速定向凝固至关重要。. 本项目重点研究新型铁基巨磁致伸缩合金快速定向凝固方法和晶体定向生长，确定其快速定向凝固行为，阐明亚稳相、择优取向和微结构演变规律及机制，阐明微量4f稀土元素FeGa合金磁致伸缩应变增强作用的物理机制，制备出高性能新型铁基巨磁致伸缩合金晶体，发展快速定向凝固理论与技术。

磁致伸缩合金在航空航天、石油增采和国防建设等领域有重要应用前景。稀土巨磁致伸缩合金性能高，但力学性能差，且成本高。新型FeGa合金力学性能好，成本低，极具发展前景，但磁致伸缩性能还较低。本项目在铁基磁致伸缩合金的功能新原理、材料新体系和制备新技术等方面取得如下研究成果：.1.发现了FeGa合金体心立方结构A2基体相中，存在modified DO3四方结构的高度共格纳米异质相，证明了FeGa合金磁致伸缩效应源于纳米相诱导的A2基体四方畸变，由此确定了FeGa合金大磁致伸缩效应的结构起源，揭示了“纳米异质结构”磁致伸缩效应新机理。.2.基于“纳米异质结构”磁致伸缩效应新机理，提出了微量固溶稀土大原子进一步增强FeGa合金磁致伸缩效应的的学术思路。采用快速凝固甩带方法（凝固速度为10的5-6次方K/s），通过强制固溶微量稀土原子与纳米相交互作用，引发基体晶格更大四方畸变，获得了超过1800ppm的巨磁致伸缩性能，比FeGa合金提高了5倍。.3.发展了快速定向凝固新方法，凝固速度在10的2次方K/s至10的4次方K/s范围内连续可调，采用微量（0.05%）Tb元素固溶的Fe基合金为对象，制备了铁基晶体材料，同步实现了微量稀土元素固溶和晶体沿<001>取向择优生长，获得了400ppm的磁致伸缩性能，比FeGa晶体（300ppm）提高30%。.在Adv Funct Mater、Acta Mater等知名学术期刊发表SCI论文32篇，授权国家发明专利4项。“新型磁弹性材料的功能调控、晶体生长及大磁致应变特性研究”获2017年度国家自然科学二等奖。蒋成保教授入选2014年度中组部领军人才计划。在第一届国际智能材料大会（WCSM-2015，韩国釜山）等学术会议上做特邀报告10余次。培养博士生4人，硕士生6人，博士生贺杨堃获校级优秀博士论文。

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