微稀土添加FeGa磁致伸缩合金轧制薄板研究

FeGa alloy is a new kind of magnetostrictive material developed in recent years, and expected to be widely used in micro-actuator and underwater acoustic transducer. However, FeGa magnetostrictive alloys are limited in practical application owing to the serious eddy current loss. Currently, the preparation of rolled FeGa sheets has become an important research subject. FeGa binary alloys are prone to brittle failure and intergranular crack during severe plastic deformation. Mechanical properties were improved by adding B, Cr, Mo and Nb. Unfortunately, the rolling process is complex and unsatisfied magnetostrictive properties could be acquired. Our recent research in rare earth (R) doped FeGa alloys indicated that trace doping rare earth in FeGa alloy can both improve mechanical and magnetostrictive properties. Thus, it is expected to acquire excellent magnetostrictive properties in rolled FeGaR sheets. In this project, we plan to prepare FeGaR rolled sheets by controlling rare earth precipitation. Rare earth precipitation in FeGaR rolled sheets will be investigated during recovery and recrystallization. It would be revealed about how the R precipitates act on the texture formation and evolution. Relationship between rare earth precipitates, texture evolution and magnetostriction would be elucidated. Finally, a trace rare earth enhanced strong <001> textured FeGa sheet would be developed.

FeGa合金是一种新型磁致伸缩材料，在高精度微位移控制、深海探测等领域有重要应用前景。然而涡流损耗问题制约该合金的应用，制备FeGa合金薄板已经成为该领域研究热点。.FeGa合金塑性低，传统轧制工艺无法成型。国际上通过添加B元素等改善了力学性能，但其轧制工艺复杂，且磁致伸缩效应低。我们前期研究发现：微量稀土元素添加FeGa合金，同时提高磁致伸缩效应和力学性能，为制备高磁致伸缩效应的FeGa合金薄板奠定了重要基础。.本课题以微量稀土添加FeGa合金为研究对象，拟深入研究薄板轧制中微量稀土的存在形式、析出行为，织构形成和演变，及其对磁致伸缩效应和力学性能的作用。从而，揭示出微量稀土添加FeGa合金在变形、回复、再结晶过程的富稀土相析出行为，阐明富稀土析出相对<001>织构形成和演化的作用机制，确定强<001>织构形成的关键控因素，制备出强<001>织构的微量稀土添加FeGa磁致伸缩合金薄板。

Fe-Ga合金是一种具有潜在应用前景的磁性功能材料。为追求磁致伸缩和力学性能双提升，本课题设计了(Fe0.83Ga0.17)100-xTbx (x=0-0.5)合金系，研究了稀土元素Tb的掺杂对Fe-Ga合金的微观组织形态、Tb元素存在形式、磁致伸缩性能及力学性能的作用规律。在定向凝固合金中，冷却速度较快，基体相生成<100>择优取向的柱状晶，Tb元素固溶度提高，析出相含量锐减，小尺寸析出相弥散分布在合金（亚）晶界处。值得注意的是，析出相与基体相存在半共格的位向关系，相界面上周期性地出现错配位错，导致基体相晶格畸变，形成局域应力场。在铸态和定向态下获得3.5 %和6.6 %的延伸率，是二元Fe-Ga多晶合金的7倍且远超Fe-Ga单晶合金的拉伸应变。合金力学性能的优化主要是由于基体相与析出相之间的交互作用引起断裂方式的改变导致的，在微量Tb掺杂的铸态和定向态合金中均发现了韧性断裂特征，表明第二相诱导合金的韧化。而Tb含量过高时，大量析出的脆性相对合金的延展性起到反作用，引起断裂应变的显著下降。探索了大原子在Fe-Ga合金中诱发巨磁致伸缩效应的结构起源，发现通过快速凝固将微量的大原子Tb强制固溶到基体中，在基体中产生了强烈的001晶格畸变，从而产生宏观的巨磁致伸缩效应。通过高温热处理技术调控Tb元素在Fe83Ga17合金薄带中的固溶度，发现随着热处理时间的增加，Tb元素发生扩散、偏聚，以2:17R相的形式析出，在此过程中A2基体的四方畸变程度逐渐降低，导致了合金磁致伸缩性能的剧烈降低。这一结果从反面证明了Fe-Ga-Tb合薄带中的巨磁致伸缩效应确实是由Tb固溶引起的。采用一系列轧制工艺成功制备出了合金薄板，合金薄板热处理过程中，随着温度的升高及时间的延长，薄板经历了再结晶、晶粒长大、晶粒长大被抑制的过程，富稀土第二相的分布状态经历了细小弥散分布、球状团聚分布、呈网状分布在晶界上的过程。确定了富稀土第二相是一种“贫铁、富铽”的高熔点第二相，在热处理过程中作为钉扎点阻碍晶界的移动。薄板在热处理中未发生异常长大过程，且热处理织构与轧制织构有一定的遗传关系。