Positive excess volume of liquid Fe-Cu alloys resulting from liquid structure change

The densities of liquid Fe-Cu alloy system were investigated in the temperature range of 1200-2000 K, covering both a superheating range and a large metastable undercooled regime. For all the Fe_xCu_100 − x (x=0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100) alloys, the density is a linear function of temperature. In all the cases, the densities of Fe-Cu alloys with different compositions are smaller than those of ideal solution. This indicates that Fe-Cu alloys deviate from ideal solution and have positive excess volumes. Furthermore, the liquid structure change is described by the pair distribution function and the coordinate number for different liquid Fe-Cu alloys. It is revealed that the atomic packing degree is responsible for the positive excess volume. Moreover, the thermal expansion coefficients are also derived and display a rise with the increase of Cu content.     

Predicting macroscopic thermal expansion of metastable liquid metals with only one thousand atoms

Results of thermal expansion prediction from atomic scale for metastable liquid metals are reported herein. Three pure liquid metals Ni, Fe, and Cu together with ternary Ni₆₀Fe₂₀Cu₂₀ alloy are used as models. The pair distribution functions were employed to monitor the atomic structure. This indicates that the simulated systems are ordered in atomic short range and disordered in long range. The thermal expansion coefficient was computed as functions of temperature and atom cutoff radius, which tends to maintain a constant when the cutoff radius increases to approximately 15 Å. In such a case, slightly more than 1000 atoms are required for liquid Ni, Cu, Fe and Ni₆₀Fe₂₀Cu₂₀ alloy, that is, the macroscopic thermal expansion can be predicted from the volume change of such a tiny cell. Furthermore, the expansion behaviors of the three types of atoms in liquid Ni₆₀Fe₂₀Cu₂₀ alloy are revealed by the calculated partial expansion coefficient. This provides a fundamental method to predict the macroscopic thermal expansion from the atomic scale for liquid alloys, especially in the undercooled regime.     

High Bs nanocrystalline Fe84−x−yCuxNbySi4B12 alloys (x=0.0-1.4, y=0.0-2.5)

In this study, Cu and Nb content dependences of magnetic properties for annealed Fe_84−x−yCu_xNb_ySi₄B₁₂ alloy ribbons fabricated by melt spinning were investigated. In Fe_83−xCu_xNb₁Si₄B₁₂ alloy systems, the coercivity H_c markedly decreases with increasing x and exhibits a minimum at around x=1.0-1.2, while the saturation magnetic flux density B_s shows a slight variation. In Fe_83−yCu₁Nb_ySi₄B₁₂ alloy systems, H_c markedly decreases at around y=0.5, while B_s shows a monotonic decrease. Fe₈₂Cu₁Nb₁Si₄B₁₂ nanocrystalline alloy ribbons exhibit a high B_s of 1.78 T and a low H_c of 3.2 A/m. The core losses of the present alloys at 1.0 T at 400 Hz, P_10/400, and at 1.0 T at 1 kHz, P_10/1k, are 1.3 and 4.4 W/kg, respectively.     

Phase formation in undercooled NdFeB alloy droplets

Small droplets of Nd_xFe_100−1.5xB_0.5x alloys (x=11.8–15) were undercooled and solidified using the drop tube technique for the purpose of studying metastable phase formation in this technically important alloy system. It was found that primary γ-Fe phase has been suppressed in most of the droplets due to significant undercooling levels achieved prior to solidification. Consequently, the primary crystallization either of metastable Nd₂Fe₁₇B_y (y≈1) phase or of Nd₂Fe₁₄B phase has been favored. The former occurs predominantly to low Nd alloys (x=11.8–13), while the latter prevails in Nd-rich alloys (x=14–15). By means of thermomagnetic analysis and powder X-ray diffraction analysis, it was determined that the metastable Nd₂Fe₁₇B_y phase has a Curie temperature of about 100°C and a hexagonal structure with lattice parameters as a=0.496 and c=0.416 nm.     

液态三元Ni-Cu-Fe合金比热的实验与计算研究

采用电磁悬浮落滴式量热方法测定了液态三元Ni₆₀Cu₂₀Fe₂₀合金在1436—2008K温度范围内的比热,实验获得的最大过冷度达232K(0.14T_L),结果表明比热值为33.27J·mol^-1·K^-1,并且随温度变化很小.在实验基础上,根据分子动力学方法结合嵌入原子势(EAM)和Quantum Sutton-Chen多体势(QSC)对比热进行了理论计算,揭示 关键词： 液态合金 比热 电磁悬浮 分子动力学计算     

Structural and magnetic correlation of Finemet alloys with Ge addition

The correlation between saturation magnetization and the magnetic moment per Fe atom in the nanocrystalline state is studied for Finemet-type alloys. These studies were performed on nanocrystalline ribbons whose compositions were Fe_73.5Si_13.5−xGe_xNb₃B₉Cu₁ (x=8, 10 and 13.5 at%). We used a simple lineal model, X-ray diffraction and Mössbauer spectroscopy data to calculate the magnetic contribution of the nanocrystals and the results were contrasted with the measured saturation magnetization of the different alloys. The technique presented here provides a very simple and powerful tool to compute the magnetic contribution of the nanocrystalline phase to the alloy. This calculus could be used to determine the volume fraction of nanocrystalline and amorphous phases in the nanocrystallized alloy, without using a very sophisticated microscopy method.     

机械合金化Fe100-xCux体系的X射线吸收精细结构研究

利用X射线吸收精细结构(XAFS)方法研究机械合金化制备的Fe_100-xCu_x(x=0,10,20,40,60,70,80,100,x为原子百分比)合金中Fe和Cu原子的局域环境结构.对于Fe_100-xCu_x(x≥40)二元混合物,球磨160h后,Fe原子的近邻配位结构从bcc转变为fcc,但Cu原子的近邻结构保持其fcc不变.与之相反,在Fe₈₀Cu₂₀和Fe₉₀Cu₁₀(x≤20)合金中,Fe原子的近邻配位保持其bcc结构而Cu原子的近邻配位结构从fcc转变为bcc结构.XAFS结果还表明,fcc结构的Fe_100-xCu_x样品中Fe的无序因子σ(0.0099nm)比bcc结构的Fe_100-xCu_x中的σ(0.0081nm)大得多;并且在机械合金化Fe_100-xCu_x(x≥40)样品中Fe原子的σ(0.0099nm)比其Cu原子的σ(0.0089nm)大.这表明机械合金化Fe_100-xCu_x样品中Fe和Cu原子可以有相同的局域结构环境但不是均匀的过饱和固溶体,而是由Fe富集区和Cu富集区组成的合金.我们提出互扩散和诱导相变机理来解释在球磨过程中Fe_100-xCu_x合金产生从bcc到fcc和从fcc到bcc变化的结构相变 关键词： XAFS 100-xCu_x合金')" href="#">Fe_100-xCu_x合金 机械合金化     

Long-term stability of soft magnetic properties of amorphous and nanocrystalline alloys based on iron

In the present paper long-term stability of magnetic properties of different amorphous and nanocrystalline alloys was studied. Magnetic properties were measured for annealed samples (300<Ta<900 K) directly after annealing and after long-term aging at room temperature. It was shown that for the Fe_75.3Cu₁Zr_1.7Si₁₃B₉ alloy magnetic permeability of the optimized samples is stable during 8 years aging. For Fe_86−xNb_xB₁₄ alloys the observed long-term instability (3 years aging) is due to annealing out of free volume leading to formations of small iron clusters coherent with the amorphous surroundings.     

First-principle study of the structural, electronic, and magnetic properties of amorphous Fe-B alloys

The structural, electronic, and magnetic properties of amorphous Fe_100−xB_x alloys (x=9, 17, 25, 27.3, 33.3, 36.3) are investigated using first-principles calculations. In these amorphous alloys, the short-range order is manifested as a series of Fe- or B-centered polyhedra such as tricapped trigonal prism, icosahedron, and bcc-like structural unit. The electron densities of states of the amorphous alloys resemble those of crystalline Fe borides, which further confirm the similarity of the local order in the amorphous and crystalline phases. All B atoms carry small negative moments of about −0.1μ_B, while small negative moments are also found on very few Fe sites for the Fe-rich compositions (x=9, 17). The average magnetic moment per Fe atom decreases nonlinearly with increasing B composition, which can be associated with the nonlinear relationship between mass density and composition.     

Al versus Si competition in FeSiAl alloys

In FeSiAl alloys, when Si substitutes for Al, important changes take place in the magnetism as well as in the structural properties. Alloys in the two composition series Fe₇₅Al_25−xSi_x (x=0, 7.5, 12.5, 17.5, 25) and Fe₇₀Al_30−xSi_x (x=0, 9, 15, 21, 30) were prepared by induction melting; afterwards they were crushed and then annealed in order to recover the DO₃ stable phase. The deformed FeAl samples show larger lattice parameters than the ordered ones; however, this difference (Δa) decreases when Si substitutes for Al until it becomes zero (i.e. until the ordered samples and the deformed ones have the same lattice parameters). This trend is the same for both sample series and does not depend on the Fe content of the alloy. However, the magnetization has a different behaviour depending on the Fe content. For deformed Fe₇₅Al_25−xSi_x alloys the saturation magnetization decreases with increasing Si content while for Fe₇₀Al_30−xSi_x deformed alloys the saturation magnetization has a plateau in which the saturation magnetization values do not vary.     

Microstructure evolution of undercooled Fe-Co-Cu alloys

Rapid solidification of undercooled Fe-Co-Cu alloys was investigated by means of fluxing purification and cyclic superheating technique. A transition in microstructure from dendrites to phase-separation occurred above a phase-separation undercooling ΔT_sep. When ΔT<ΔT_sep, dendrite was observed, the trunks were rich in Fe and Co, while Cu was rich at inter-dendrites. However, the phase-separated microstructure was obtained once ΔT>ΔT_sep, with a large sphere of L1 phase located almost at the center of the sample and enwrapped by L2 phase. ΔT_sep was 222, 88 and 45 K for Fe₅₀Co₃₀Cu₂₀, Fe₂₅Co₂₅Cu₅₀ and Fe₁₅Co₁₅Cu₇₀ alloys in this work, respectively. It was investigated that L1 phase solidified before L2 phase after liquid separation and followed different ways.     

Synthesis and magnetic properties of ferrites spinels MgxCu1−xFe2O4

Polycrystalline Mg_0.6Cu_0.4Fe₂O₄ ferrites have been prepared using solid-state reaction technique. Their structural and magnetic properties have been studied, using X-ray diffraction and magnetic measurements.Using mean field theory and high-temperature series expansions (HTSE), extrapolated with the padé approximants method, the magnetic properties of Mg_1−xCu_xFe₂O₄ have been studied. The nearest neighbor super-exchange interactions for intra-site and inter-site of the Mg_1−xCu_xFe₂O₄ ferrites spinels, in the range 0≤x≤1, have been computed using the probability approach, based on Mössbauer data. The Curie temperature T_c is calculated as a function of Mg concentration. The obtained theoretical results are in good agreement with experimental ones obtained by magnetic measurements.     

The evolution of covalent bonding structures of liquid In–Sn alloys

The short-range orders of liquid In_xSn_100−x binary alloys have been investigated along the liquidus based on the experimental results obtained using X-ray diffraction. The covalent bonding structures characterized by the shoulder on the high-Q side of the first peak of S(Q) for all the In_xSn_100−x melts are detected. With increasing Sn content, there is a rather continuous change of the local structure possibly related to the presence of nearly covalent bonds in the liquid alloy. The peculiar temperature dependence of the viscosity is assigned to the evolution of tetrahedral units. The observed correlation between liquid structures and peculiar viscosity behaviors provides new insight into nucleation phenomena from microscopic viewpoint.     

First-principle calculations of dilute nitride GaP1−xNx alloy in zinc-blende structures

First-principle plane-wave pseudopotential calculations using the density-functional theory within the local density approximation (LDA) have been carried out to investigate the structural, electronic and thermodynamic properties of zinc-blende dilute nitride GaP_1−xN_x alloy. We have found that the unit cell volumes of GaP_1−xN_x alloys are smaller than the value calculated from the linear interpolation of GaN and GaP binary alloys and there exists a negative deviation from Vegard's law. The Ga-P and Ga-N bond lengths of GaP_1−xN_x alloys reveal a slight relaxation. The incorporation of nitrogen into GaP leads to the giant reduction of the bandgap energy. We have investigated the thermal stabilities and obtained the most stable configurations of the GaP_1−xN_x alloy. In addition, the formation enthalpies have also been calculated, which could explain the difficulty in nitrogen incorporation into GaP.     

Electrical resistivity of ternary glassy and liquid Pd-alloys

The electrical resistivity of liquid (Pd₁₀₀Cu_100?x)₈₀Ge₂₀ alloys has been measured as a function of temperature. For Cu-rich negative temperature coefficients and for Pd-rich alloys positive temperature coefficients of the electrical resistivity have been observed. This behavior is very similar to recent observed resistivity temperature curves of glassy (Pd₁₀₀Cu_100?x)₈₀P₂₀ alloys. An explanation of the resistivity behavior in terms of liquid metals theory is suggested.     

Structural, magnetic properties and magnetostriction studies of Sm1−xNdxFe1.55 alloys

Structural, magnetic properties and magnetostriction studies of Sm_1−xNd_xFe_1.55 (0≤x≤0.56) alloys have been performed. X-ray diffraction analysis confirms the presence of single cubic Laves phase in Sm_1-xNd_xFe_1.55 alloys with 0≤x≤0.48. The lattice parameter of alloys increases linearly with increase in Nd content while the Curie temperature behaves in the opposite way. The alloy x=0.08 exhibits a giant magnetostriction value (λ_∥-λ_⊥) of −2187 ppm at a magnetic field of 12 kOe due to the anisotropy compensation between Sm³⁺ and Nd³⁺ ions.     

Electronic structure and optical properties of TbNi5−xCux

In this paper we present theoretical investigation of optical conductivity for intermetallic TbNi_5−xCu_x series. Within the framework of LSDA+U calculations, electronic structure for x=0, 1, 2 is calculated and additionally optical conductivity is obtained. Disorder effects of Cu for Ni substitution on a level of LSDA+U densities of states (DOS) are taken into account via averaging over all possible Cu ion positions in the unit cell for given doping level x. Gradual smoothing of optical conductivity structure at 2 eV together with simultaneous intensity growth at 4 eV corresponds to increase of Cu and decrease of Ni content.     

A Mössbauer spectroscopy and neutron diffraction study of magnetostrictive,melt-spun Fe–Ga alloy ribbons

Ribbons of Fe_100−xGa_x (x=15, 17.5, 19.5 and 22.5) were prepared by rapid solidification from the melt. ⁵⁷Fe Mössbauer spectroscopy and high resolution neutron diffraction have revealed that Fe_100−xGa_x alloys with x=15 and 17.5 have the disordered bcc (A2) structure even after annealing, but the alloy with x=19.5 developed the short-range ordered D0₃ phase when annealed. The x=22.5 alloys showed mainly D0₃ phase with a fraction of bcc phase. A fraction of the bcc phase transformed into D0₃ phase and the long-range ordering of D0₃ phase was improved after annealing. ⁵⁷Fe Mössbauer spectra showed no observable L1₂ phase in any samples even though less than 1% volume of L1₂ phases has been found in the annealed samples by neutron diffraction. The additional absorption at hyperfine field of 25 T in x=22.5 samples was regarded as a result of imperfect D0₃ structure, rather than L1₂ phase.     

Critical behaviour and magnetic properties of A-B spinel ZnxCu1−xFe2O4

Polycrystalline Zn_0.6Cu_0.4Fe₂O₄ ferrites have been prepared using a solid-state reaction technique. Their structural and magnetic properties have been studied, using X-ray diffraction and Mössbauer and magnetic measurements. These results have been compared to a more general theoretical study, on Zn_xCu_1−xFe₂O₄, based on mean field theory and high-temperature series expansions (HTSE), and extrapolated with the Padé approximant method. The nearest neighbour super-exchange interactions for the intra-site and the inter-site of Zn_xCu_1−xFe₂O₄ spinel ferrites, in the range 0≤x≤1, have been computed using the probability approach, based on Mössbauer data. The Curie temperature T_C is calculated as a function of Zn concentration. The theoretical results obtained are in good agreement with the experimental results obtained by magnetic measurements.