L10 Ordering in MnAl and FeNi Influenced by Magnetic Field and Strain
L10 Ordering in MnAl and FeNi Influenced by Magnetic Field and Strain
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MnAl 和 FeNi 中 L10 有序度受磁场和应变的影响
DOI：
10.1093/micmic/ozad067.690
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发表时间：
2023
影响因子：
2.8
通讯作者：
Lewis, Laura H
中科院分区：
文献类型：
--
作者：
Han, Chaoya;Lejeune, Brian;Zhang, Xiaoyu;Ni, Chaoying;Lewis, Laura H
由于各种材料供应链的挑战，无约束元素的磁体吸引了越来越多的兴趣[1]。磁性材料，如不含稀土的FeNi和MnAl，由于其独特的化学有序的四方晶系晶体结构（表示为L10结构）所具有的高磁晶各向异性和其他相关磁性，一直受到相当大的关注[2 - 4]。然而，由于Fe和Ni的原子迁移率极低，L10 FeNi的合成成功有限[5]。在这项工作中，同构MnAl首先研究了代理，以了解L10有序过程。此外，来自TEM研究的FeNi中的L10有序的证据，其中有序的应用程序提供的应变和磁场的热处理过程中的严重塑性变形的FeNi合金促进。MnAl样品通过在氩气气氛中熔融纺丝（MS）来合成，以产生包含非平衡α-相（六方密堆积结构）的薄带，所述非平衡α-相是L10相的前体。为了诱导化学有序，样品在390 ℃下等温退火15分钟，其中静磁场（μ 0H = 600 Oe）的影响来自形成闭合磁通路径的两个SmCo磁体。从具有93%应变的冷轧（CR）样品中提取两个每个为1 cm x 7 cm x 0.3 mm的FeNi带样品。这些样品之一，标记为FSA（"场应变退火"），在285 ℃下在N2中进一步退火48天[2]。在退火过程中，平行于轧制方向施加10 MPa的拉伸应力和0.7 T的磁场。Carl Zeiss Auriga® 60 CrossBeam®聚焦离子束工具和扫描电子显微镜（FIB/SEM）用于成像和用于制备TEM横截面样品。使用具有EDAX检测器的JEM-2010F（200 kV）系统进行TEM成像和能量色散光谱（EDS）。图1a中的TEM图像呈现了FIB研磨、场退火的MnAl带的横截面视图。选区电子衍射（SAED）分析表明，在该样品中MnAl的两个相共存;这些是残留的γ-相和有序的τ-相（L10结构）。图1b是从图像中的圆圈区域获得的衍射图案，其示出了包含τ相超晶格反射的暗对比度晶粒。虽然检测到具有不规则晶界的相对大的τ相晶粒，但图1a中，大多数τ相晶粒看起来是层状的，并且与α相层状交替分布，如图1c中标记为τ + α的区域所示。这种形态是典型的马氏体相变，与文献[4]中的其他观察结果一致。据观察，这种层状结构通常从原始α相晶界或从界面开始。此外，在靠近薄带初始淬火区的区域，τ相晶粒密度较高，表明熔体快淬过程中产生的残余应变促进了τ相的异质形核和马氏体相变。FIB制备的冷轧（CR）和场应变退火（FSA）FeNi试样横截面的TEM图像如图2a和2b所示。如图1a所示，在CR试样中检测到由尺寸约为2 μ m x 200 nm的细长晶粒组成的冷轧织构{112}。< 111>在热能的协同作用下（温度远低于...
Due to various materials supply chain challenges, magnets free of constrained elements are attracting increasing interest [1]. Magnetic materials such as rare-earth free FeNi and MnAl have been receiving considerable attention due to the high magnetocrystalline anisotropy and other associated magnetic properties derived from their unique chemically ordered tetragonal crystal structure, denoted as the L10 structure [2-4]. However, synthesis of L10 FeNi has had limited success due to the extremely low atomic mobilities of Fe and Ni [5]. In this work, isostructural MnAl was first studied as proxy to understand the L10 ordering process. Furthermore, evidence of L10 ordering in FeNi derived from TEM studies is presented, where ordering was facilitated by the application of strain and magnetic field provided during thermal treatment of a severely plastically deformed FeNi alloy. The MnAl samples were synthesized by melt-spinning (MS) in an argon atmosphere to produce thin ribbons containing the non-equilibrium ϵ-phase (hexagonal close-packed structure), which is the precursor to the L10 phase. To induce chemical order, a sample was isothermally annealed at 390 C for 15 minutes with the influence of a static magnetic field (μ0H= 600 Oe) derived from two SmCo magnets that formed a closed flux path. Two FeNi ribbon specimens of 1 cm x 7 cm x 0.3 mm each were extracted from a cold-rolled (CR) sample with 93% strain. One of these samples, labeled as FSA (“field-strain annealed”), was further annealed in N2 at 285 C for 48 days [2]. During the annealing process, a tensile stress of 10 MPa and a magnetic field of 0.7 T were applied parallel to the rolling direction. A Carl Zeiss Auriga® 60 CrossBeam® focused ion beam tool and a scanning electron microscope (FIB/SEM) were used for imaging and for the preparation of TEM cross-sectional specimens. TEM imaging and energy-dispersive spectroscopy (EDS) were performed using a JEM-2010F (200 kV) system with an EDAX detector. The TEM image in Figure 1a presents a cross-section view of FIB-milled, field-annealed MnAl ribbon. Selected-area electron diffraction (SAED) analysis reveals that two phases of MnAl coexist in this sample; these are the residual ϵ-phase and the ordered τ-phase (L10 structure). Figure 1b is a diffraction pattern obtained from the circled region in the image which shows a darkcontrast grain that contains τ-phase superlattice reflections. Although relatively large τ-phase grains with irregular grain boundaries are detected, Figure 1a, most τ-phase grains appear to be lamellar in shape and are alternatively distributed with the ϵ-phase lamellae, as shown in the area labeled as τ+ ϵ in Figure 1c. This morphology is typical of a martensitic phase transformation, consistent with other observations in literature [4]. It is observed that this lamellar structure generally starts from an original ϵ-phase grain boundary or from an interface. Additionally, a higher density of τ-phase grains appears to be distributed in the region close to the initial quenched region of the ribbon, suggesting that residual strain arising from the melt spinning process may promote the heterogeneous nucleation of τ phase and the martensitic phase transformation. TEM images of FIB-prepared cross-sections of the cold-rolled (CR) and field-strain annealed (FSA) FeNi specimens are shown in Figure 2a and 2b. A cold rolling texture {112}< 111> consisting of elongated grains with approximate dimensions 2 μm x 200 nm, as shown in Figure 1a, was detected in the CR specimen. Recrystallization occurred in the FSA specimen (Figure 1b) under the synergistic effect of thermal energy (at a temperature well below the …