Crystallization of Fe-B amorphous alloy powders produced by chemical reduction

The crystallization behaviour of the Fe?B amorphous alloy powders prepared by the chemical reduction method has been investigated by Mössbauer spectroscopy. In comparison to amorphous ribbons prepared by melt-spinning, a different crystallization behaviour has been observed. After annealing the amorphous samples entirely crystallized into three crystalline phases: α-Fe, Fe₃B, and Fe₂B. In the case of Fe₈₀B₂₀ amorphous alloy ribbons produced by melt-spinning technique eutectic crystallization is commonly observed and results in the crystalline phases: α-Fe and Fe₃B. This kind of crystallization was not observed in the chemically prepared samples. The metastable tetragonal Fe₃B phase transformed completely into α-Fe and Fe₂B after annealing at 973 K for one hour.     

自催化沉积非晶态复合材料的组成与晶化特性研究

用自催化沉积非晶态(Ni,Cu)_100-xP_x+SiC复合材料,研究了复合材料的组成与晶化特性,结果表明,当x>14或者SiC体积分数小于12.8%时,复合材料即保持非晶态;时效温度达到603—618K,复合材料逐渐向晶态过渡,晶化相为fc c Ni和Ni_yP_z,稳定组织为(Ni,Cu)P+Ni₃P+SiC.较非晶态复合材料,晶态材料具有更高的力学性能. 关键词：     

Crystallization of mechanically alloyed amorphous W-Mg alloy under high pressure

Pure metal powder mixtures of W and Mg at the desired composition were milled in conventional high-energy ball mill, and amorphous alloy W₅₀Mg₅₀ was obtained after milling for 20 h. The structure evolution of elemental powder mixtures was studied following milling and subsequent high pressure and high temperature treatment. The amorphous alloy transform into a nanocrystalline material below 1050 °C at 4.0 GPa. On increasing the temperature, it transforms into a mixture of several new crystal phases under high-pressure condition. It also found that both mechanical alloying and high pressure treatment are the two necessary processes to form the nanocrystalline and the new phases.     

Structure and magnetic properties of nanocrystalline soft ferromagnets

The structure and magnetic properties of soft magnetic nanocrystalline composites crystallised from amorphous ribbons are reviewed. The Fe-Early Transition Metal-Boron (Nanoperm-type) nanostructures are discussed in details and compared to the Si containing (Finemet) alloys. The nanocrystallization process was studied by calorimetry; the spatial dimension, the composition and the relative fraction of the bcc and the residual amorphous phases were investigated by X-ray diffraction and Mössbauer spectroscopy. A small fraction of Fe atoms (about 4%) was found which cannot be assigned either to the residual amorphous or to the bcc phase. It is suggested that the magnetic anisotropy of the bcc phase is decreased due to the dissolved Zr and B impurities. The Curie point and Fe atomic moments in the residual amorphous tissue are determined and compared to that of a macrosized amorphous phase of similar composition. The observed deviations do not scale with the average characteristic size of the amorphous phase and thus cannot be explained in the framework of the existing models. Magnetic dipolar coupling and tensile stresses between the grains of the different phases are suggested for explaining the soft magnetic behaviour of the nanostructures.     

小角X射线散射表征非晶合金纳米尺度结构非均匀

表征纳米尺度结构非均匀对于理解非晶合金的变形、弛豫等动力学行为至关重要.受时空尺度限制,非晶合金纳米尺度结构非均匀的实验表征具有很大的挑战性.本文针对一种典型的锆基非晶合金,开展了同步辐射小角X射线散射原位拉伸实验.通过对散射曲线的定量分析,揭示了非晶合金在纳米尺度的非均匀结构图像.首先,Porod散射曲线呈现正偏离行为,表明非晶合金属于非理想两相散射体系,两相界面弥散且任一相内都存在电子密度涨落.基于散射曲线的Guinier定律分析,进一步揭示非晶合金中散射体形状远偏离球形,其特征尺度主要分布在0.8—1.6 nm之间,且在弹性变形阶段几乎不变.最后,通过Debye相关函数分析,发现这些纳米尺度散射体仅在1 nm之内存在强关联,符合非晶合金短程有序、长程无序的结构特征.研究结果表明非晶合金中存在具有复杂空间分布的纳米尺度非均匀结构.     

Partial crystallization of an amorphous alloy by electronic energy deposition

The first experimental evidence is reported of crystallization induced in an amorphous alloy by a high density of electronic excitation deposited along the path of swift heavy ions. The formation of nanocrystalline iron boride phases was observed in an amorphous Fe73.5Cu1Nb3Si13.5B9 alloy irradiated at low temperature with 5 GeV Pb ions up to fluences of 1 x 10(11) ions cm-2. No evidence for the formation of the Fe(Si) phase was found. This phenomenon was interpreted in terms of the relaxation of the high level of energy deposited in electronic excitations along the path of Pb ions in the target, which induces extensive stress and strain that could destabilize the amorphous structure.     

Magnetic properties of soft magnetic composites prepared with crystalline and amorphous powders

Physical properties of soft magnetic composites prepared with a mixture of amorphous (FeSiBC) and crystalline (Fe) powders coated with distinct electrical insulator contents are reported. Density, saturation polarization, permeability and coercivity of the cores reduce linearly with the increase of the softer magnetic phase amount and a general relation can be expressed by a rule of mixtures. The behavior of the coercivity, as a function of the magnetic phase content, differs from that previously reported for magnetic composites prepared with equal amounts of magnetic and non-magnetic phases. For frequencies upto 1 kHz the magnetic losses of the cores are constant, following the same behavior of the coercivity. A qualitative explanation of the behavior of the latter is addressed based on an expression applicable for crystalline and amorphous materials.     

Laser formed amorphous Fe-based alloy

the amorphous layers were obtained using the method of CW CO_2 laser scanning Fe-based alloy surface. The function of structure of Fe-based alloy, scanning speed, cooling method etc. for laser-formed amorphous state were discussed. A much thick amorphous layer can be made by laser scanning.     

Mössbauer study of the amorphous alloy with and without ion implanted

Amorphous alloys as a new magnetic materials have very important significance for both basic researches and applications. The CO, N ion-implanted amorphous Fe?B?Si?C alloys were studied by using X-ray diffraction, magnetic measurement and Mössbauer effect. It was shown that this amorphous alloys can be crystallized in different degree and in different phases by different kind and dose of implanted ions. The crystallization process was started in surface layer and then spread into interior.     

Influence of composition on hyperfine interactions in FeMoCuB nanocrystalline alloy

Influence of varying Fe/B ratio upon hyperfine interactions is investigated in the Fe_91?x Mo₈Cu₁B_x rapidly quenched alloys. They are studied both in the as-quenched (amorphous) state as well as after one-hour annealing at different temperatures ranging from 330 °C up to 650 °C. Such a heat treatment causes significant structural changes featuring a formation of nanocrystalline bcc-Fe grains during the first crystallization step. At higher annealing temperatures, a grain growth of bcc-Fe and occurrence of additional crystalline phases are observed. The relative fraction of the crystalline phase governs the development of magnetic hyperfine fields in the residual amorphous matrix even if this was fully paramagnetic in the as-quenched state. The development of hyperfine interactions is discussed as a function of annealing temperature and composition of the investigated alloys. ⁵⁷Fe Mössbauer spectrometry was used as a principal analytical method. Additional information related to the structural arrangement is obtained from X-ray diffractometry. It is shown that in the as-quenched state, the relative fraction of magnetic hyperfine interactions increases as the amount of B rises. In partially crystalline samples, the contribution of magnetic hyperfine interactions inside the retained amorphous matrix increases with annealing temperature even though the relative fraction of amorphous magnetic regions decreases.     

Microstructural characterization of rapidly solidified Al 90 Ce 10 alloy

In the present work, the microstructure of the melt-spun Al 90 Ce 10 alloy has been characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM) together with energy-dispersive spectrometry. It has been found that the microstructure of the melt-spun Al 90 Ce 10 alloy is composed of the amorphous phase, f-Al, f-Al 11 Ce 3 , Al 3 Ce and unidentified phases, quite different from that of the ingot-like alloy consisting of coarse primary f-Al- f-Al 11 Ce 3 dendrites embedded in the f-Al- f-Al 11 Ce 3 eutectic matrix. Moreover, the amorphous phase is dominant in the melt-spun Al 90 Ce 10 alloy according to the XRD and TEM results. Al 3 Ce particles, less than 100 nm in size, are dispersed in the partial amorphous phase. Polygonal f-Al 11 Ce 3 crystals embedded in the f-Al matrix are also observed. The presence of the hexagonal, kite-like and petal-like intermetallic particles surrounded by the amorphous phase indicates that there exist micro-inhomogeneous structures in the Al 90 Ce 10 melt. These results demonstrate that the overheating of the melt has a significant effect on the amorphization of the Al 90 Ce 10 alloy.     

Lithium Storage Property of Graphite/AlCuFe Quasicrystal Composites

Quasicrystals have long-range quasi-periodic translational ordering and non-crystallographic rotational symmetry.Al-Cu-Fe quasicrystals have great potential for lithium storage because of their high Al content and a large number of defects in the structure.In our previous study(J.Alloys Compd.805(2019)942)we showed that Al-Cu-Fe quasicrystals have good initial capacity whereas its cycle stability is poor.In the present study,graphite/AlCuFe is prepared by the mechanical alloying method.The results show that graphite/AlCuFe quasicrystal composites are successfully synthesized by planetary ball milling at 550 rpm for 80 h.The quasicrystal particle size decreases and the amorphous graphite forms onion-like carbon(OLC)when the two phases mix evenly.OLC forms on the surface of the Al-Cu-Fe quasicrystalline powder.Charge and discharge tests show that graphite/AlCuFe quasicrystal composites have high-stability capacity of 480 mAh/g after 20 cycles,which is larger than the sum of capacities of graphite and Al-Cu-Fe quasicrystals.     

Phase transformations of the amorphous Zn-Sb alloy under high pressures

Abstract

Phase transformations occurring in initially amorphous Zn₄₁ Sb₅₉ semiconductor at pressures to 10 GPa and temperatures to 350C were studied using the measurement of electrical resistance, in situ energy dispersive X-ray diffraction and neutron diffraction on quenched high-pressure phases at ambient pressure. The studied T- P region involves the regions of reversible and irreversible crystallisation and phase transitions between the equilibrium crystalline low-pressure and high-pressure phases.     

Local structure of Fe70Cr15B15 X-ray amorphous alloy

The local atomic and magnetic structure of Fe₇₀Cr₁₅B₁₅ X-ray amorphous alloy is studied by means of ¹¹B nuclear magnetic resonance (NMR) and ⁵⁷Fe Mössbauer spectroscopy. It is determined that Fe₈₅B₁₅ and Fe₇₀Cr₁₅B₁₅ X-ray amorphous alloys consist of microregions (nanocrystals) with short-range orders of t-Fe₃B and α-Fe phases. It was found out that chromium atoms in the Fe₇₀Cr₁₅B₁₅ X-ray amorphous alloy are evenly distributed in these two nanocrystals, forming t-(Fe,Cr)₃B and α-Fe(Cr) phases.     

Fast degradation of azo dye by nanocrystallized Fe-based alloys

Exploring new alloys with high efficiency in degrading organic pollutants in aqueous solutions is of wide interests. Here, we report that the nanocrystallized Fe_(82.65)Si_4B_(12)Cu_(1.35) alloy exhibits higher efficiency in decolorizing azo dye solutions compared to its amorphous counterpart. The increased efficiency is attributed to the formation of numerous microbatteries between the α-Fe(Si)and Fe_2 B nanocrystalline phases, which exhibit different corrosion potentials. These results suggest that nanocrystallized Fe-based amorphous composites hold promising application potential in degrading azo dyes solutions.     

典型高分子材料的固体核磁共振研究

本论文通过固体核磁共振（NMR）谱及动力学参量的测量,并结合X-射线衍射技术和DSC测量等研究了两种典型高分子材料的相结构、链的运动以及相与相之间的关系.  乙烯-醋酸乙烯共聚物( EVA) 是最主要的乙烯共聚物之一. 研究发现,EVA的相组成非常复杂,共有5个不同的组分. 除了PE中所观察到的常规单斜晶相和刚性的正交晶相外,我们发现还存在第三个晶相分量－运动性较强的晶相（SOCP,可能是转动相）. 它不仅拥有自己的熔点,而且它的化学位移和分子运动性不同于刚性正交晶相（LOCP）. 另一方面,非晶相也由两种不同的分量组成：运动受限的各相异性的非晶界面相和高度可动的橡胶型的非晶相. 我们进一步详细研究了EVA中的晶区链动力学和非晶区的低温冻结行为. 实验发现,在正交晶相中,高分子链以180° flip-flop方式运动,同时伴随沿链方向的平移型跳跃运动,并引起正交晶相和非晶相之间的长程链扩散,通过NOE的测量证实了这种相间链扩散的存在,并进一步通过实验证实这种相间链扩散是一种受限扩散而不是自由扩散. 同时非晶相的两个组分具有不同的低温冻结行为：当温度低于-弛豫转变温度时,橡胶型的非晶相中的长程分子运动被冻结,但仍存在分子的局域运动;而界面非晶在低温时冻结成一种有序取向结构,并用质子自旋扩散实验证实该有序结构与正交晶相相邻近.  少量纳米级片层状粘土分散在聚合物中就可赋予材料许多优异的性能,我们用固体NMR技术对EVA/REC复合材料的结构和其中粘土的分散性质进行研究,发现上述复合材料中所形成的晶体类型不仅依赖于各组分的性质还依赖于所形成的复合材料的类型.  偏氟乙烯/三氟乙烯共聚物（P（VDF-TrFE））是最主要的铁电高聚物之一. 我们利用变温固体¹⁹F MAS NMR 谱及弛豫数据的测量详细研究了电子辐照对P(VDF-TrFE)共聚物的分子结构、构型、运动性以及相变等的影响. 发现,电子辐照不仅改变了分子链段的构型和运动性,同时也改变了局部分子化学结构. 电子辐照促使铁电相向顺电相(或者非晶相)转变,与此同时诱发了富含VDF和含-TrFE链段从全反式的构型到混合的反式-旁式构型的转变. 电子辐照加剧顺电区域中的分子运动而在高温熔融态中(>100 ℃）,分子的运动反而受限.     

Structure evolution of a zirconium-based amorphous alloy upon megaplastic strain in the bridgeman chamber

The structure evolution of the Zr₅₀Ni₁₈Ti₁₇Cu₁₅ massive metal glass upon megaplastic strain (MPS) in the Bridgeman chamber is investigated in a wide interval of strain degrees at room temperature. It is demonstrated that upon MPS with n = 1/2 rotation of the Bridgeman anvil, nanocrystalline phases are precipitated in the alloy. With increasing strain, these phases are dissolved. It is suggested that nucleation centers of nanocrystalline phases (nanoclusters) are formed in the amorphous matrix upon MPS under compression without shear in the Bridgeman chamber. These phases grow in the shear bands transforming into the nanocrystalline phase upon MPS.     

Effect of ionic liquid on chain segment motion and charge detrapping in poly(l-lactide)/ionic liquid composites

The effect of ionic liquid on the chain segment motion and charge detrapping in poly(l-lactide) (PLA)/ionic liquid (IL) composites has been investigated by means of thermally stimulated depolarization current (TSDC), scanning electron microscopy, and differential scanning calorimetry. There are four current peaks (namely, α, ρ₁, ρ₂, and ρ₃ peaks, respectively) in TSDC spectra of PLA and PLA/IL composites. The α peak corresponds to the glass transition, the ρ₁ peak is attributed to space charge trapped in the amorphous phase, the ρ₂ peak is originated from space charge trapped in the interphase that includes PLA/IL interface and crystalline/amorphous interface of PLA, and the ρ₃ peak is originated from space charge trapped in the crystalline phase. With the increase of IL content from 0 to 5phr, ρ₂ and ρ₃ peaks gradually merge into one single peak. By analyzing the characteristic parameters of these peaks, it is found that IL can accelerate the mobility of chain segments and increase structural defects in PLA/IL composites. In addition, IL decreases the stability of trapped charge in both amorphous and crystalline phases, but not affecting the stability of trapped charge in interphase.     

Magnetoelectric properties of particulate and bi-layer PMN-PT/CoFe2O4 composites

Our studies comprise electrical dielectric and magnetoelectric properties of CoFe₂O₄ (CFO) and Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ [PMN-PT] magnetoelectric composites. The individual phases were prepared by conventional ceramic method. The particulate composites of ferrite and ferroelectric phases were prepared in ferroelectric rich region. Presence of both the phases in the composites was confirmed using X-ray diffraction techniques. The scanning electron microscopic images recorded in backscattered mode were used to study the microstructure of composites. Lattice constant, dielectric constant, electrical resistivity, ferroelectric, and magnetic properties of individual as well as particulate composites were studied. Further the bi-layer composites were made using the discs obtained from the powders of individual phases where hot press technique was employed to obtain disc of individual phases. CFO phase used in bi-layer composites was obtained using chemical co-precipitation technique. Magnetoelectric (ME) measurements were carried out on both, particulate and layered magnetoelectric composites. Comparison of ME signal obtained from particulate and layered composites revealed that the layered composites gives superior magnetoelectric signal. ME data obtained for layered composites show good agreement with the theoretical model.     

Time-resolved X-ray diffraction study of the transition of an amorphous TiCu alloy to the crystalline state

The transition of the TiCu alloy from an amorphous state to the crystalline state has been studied by time-resolved X-ray diffraction. An analysis of the diffraction pattern has shown that the crystallization of the amorphous TiCu alloy upon heating occurs for a short time (no longer than 0.5 s). A sharp transition is observed at the instant of crystallization, at which the intensity of the total diffraction pattern background decreases and diffraction lines of the crystalline phase γ-TiCu arise. No intermediate crystalline phases are observed. The change in the alloy structure is accompanied by the exothermic thermal effect. The kinetics of the change in the total intensity of the diffraction spectrum in the period preceding the crystallization is nonmonotonic. Ten seconds before the occurrence of diffraction lines of the γ-TiCu phase at 300°C, the integrated spectral intensity decreases. The effect observed is related to the relaxation processes in the amorphous state and the onset of formation of long-range structural order.