Short-range order of amorphous FeNiB alloy after neutron irradiation

Transmission Mössbauer spectroscopy was used to study irradiation-induced changes in the short-range order of an amorphous Fe_80-x Ni _x B₂₀ alloy. Neutron irradiation led to an increase of the width of a hyperfine field distribution implying atomic rearrangement towards disordering. Changes in a mean value of a HFD and Mössbauer line areas can be associated with a reorientation of spins due to radiation damage.     

EXAFS study of the atomic structure of amorphous Tb20Fe80

The atomic structure of amorphous Tb₂₀Fe₈₀ thin films has been studied by Extended X-ray Absorption Fine Structure (EXAFS) of both FeK and TbL _III absorption edges. The local site geometry around Fe atoms shows predominantly Fe nearest neighbors with an Fe-Fe distance distribution centered on 2.50±0.02 Å and a coordination number of 9.1±1. In contrast, the radial structure function (RSF) obtained at the Tb edge is broad and asymmetric. The peak in the RSF corresponds to a Tb-Fe near neighbor distance of 2.94±0.1 Å with no evidence for Tb-Tb nearest neighbor coordination. The width and the shape of the RSF suggest that the Tb-Fe atomic environment is anisotropic and strained probably as a consequence of the growth process. This distorted atomic environment is suggested to be responsible for the magnetic anisotropy in these alloys. Thermal annealing at 200 °C leads to reduction inK _u. We propose that this results from reordering of the Tb local environment such that the average structural anisotropy in the distribution is reduced. EXAFS data show that annealing at 400°C causes precipitation of bcc polycrystalline Fe. The addition of 7 at.% Au to the alloy prevents this recrystallization and preserves the amorphous state but does not prevent the structural relaxation which reducesK _u at lower temperatures.     

Microscopic collective dynamics of atoms in the amorphous metallic alloy Ni33Zr67

The structural properties and microscopic collective dynamics of atoms in the amorphous metallic alloy Ni₃₃Zr₆₇ are studied using molecular dynamics simulations with a pair-additive model potential. The calculated equilibrium structural and dynamic characteristics are compared with experimental data on neutron diffraction and inelastic X-ray scattering. Theoretical analysis of the structural relaxation of microscopic density fluctuations for amorphous metallic alloys is performed within the Lee’s recurrent relation approach. The results of theoretical calculations for the intensity of scattering I(k, ω) for the amorphous metallic alloy Ni₃₃Zr₆₇ are in good agreement with the results of computer simulation and experimental inelastic X-ray scattering data. The low-frequency excitations observed in the longitudinal current spectra are related to the vibrational motions of individual atom clusters, which include Ni and Zr atoms.     

Short-range order in the Fe-B-Sn amorphous system

Melt quenched FeBSn samples of different compositions were prepared with three different quenching rates and analyzed by Mössbauer spectroscopy and X-ray diffraction. In a previous work, the glass-forming tendency in this system was analyzed, In the present work, the short-range order is studied and an improvement in the determination of the glass-forming composition range is achieved. Mössbauer spectra were fit using hyperfine field distributions.     

Magnetic properties of the amorphous alloy Fe80Er20

Amorphous Fe₈₀Er₂₀ alloys were prepared with the melt spinning technique. The ribbons were investigated by Mössbauer spectroscopy from room temperature to 4.2 K. A phase transition from the paramagnetic to the ferromagnetic phase could be observed. The temperature dependence of the internal magnetic field was measured. The correlations of the hyperfine parameters were determined from the 4.2 K spectrum.     

块体非晶合金 Zr55Cu30Al10Ni5 结构弛豫的研究

应用同步辐射小角x射线散射和差示扫描量热分析对块体非晶合金Zr55Cu30Al10Ni5结构弛豫进行了研究.实验结果表明:经340℃、不同时间退火后的非晶内部的电子密度涨落随退火时间的延长先增大而后减小;玻璃转变温度附近焓弛豫峰的表观激活能则随退火时间的延长先减小而后增大.结果反映了随退火时间的延长,块体非晶合金内部类液体区不断减少及类固体区不断增加的过程.     

PES study of amorphous alloy Fe40Ni40P20

The electron structure of amorphous Fe₄₀NI₄₀P₂₀ has been investigated before and after annealing by XPS and UPS (HeI, HeII). It is shown that the spectra of UPS were modified obviously by various degree of annealing. Composition and chemical states of the components on the surface of the sample are also presented and the effect of structural ordering on the density of states (DOS) of the valence band is discussed.     

Quadrupole splitting on57Fe nuclei and local structure of the amorphous alloys Ni−Zr,Ni−Ta

Quadrupole splittings on⁵⁷Fe nuclei were studied by Mössbauer spectroscopy in amorphous and crystalline Ni-based alloys with 37 at .% Zr and 25–50 at .% Ta with 0.5 at .%⁵⁷Fe addition. Quadrupole splitting distributions and then the topological short range in Ni?Ta alloys were found to be similar to that of the Ni₃Ta intermetallic compound. The distribution of splittigs for Ni?Zr alloy is similar to that of its crystalline counterpart.     

Effect of dynamic loading on the structure of amorphous alloy Fe66Ni12Si20B2

Transmission- and depth-selective-conversion-electron Mössbauer spectroscopy (DCEMS) were applied to study variation of structural state in the bulk and in the surface layer (500, 1000, 1500 Å thick) of amorphous alloy under certain optimum conditions of the dynamic loading. The alloy structure remains amorphous. However, a certain variation of the short range order. An amorphous oxide Fe₂O₃ is formed on the amorphous alloy surface.     

Atomic structure and diffusivity in liquid Al80Ni20 by ab initio molecular dynamics simulations

The atomic structure and diffusivity in liquid Al₈₀Ni₂₀ are studied by ab initio molecular dynamics simulations. The local structures are analyzed by the pair correlation function, structure factor, coordinate number, Honneycutt–Anderson bond pair, and Voronoi tessellation methods. It is observed that the amount of icosahedral clusters increases, and the liquid becomes more ordered as the temperature decreases. The predicted self-diffusion coefficients of Al and Ni via the mean square displacements are very close to each other and agree well with the quasi-elastic neutron scattering measurements in the literature. The observation of equal self-diffusivity of Al and Ni is attributed to the formation of local solute-centered polyhedra, coupling the migration of Al and Ni. The Manning dynamic correlation factor is evaluated and found to be close to unity. The predicted interdiffusion coefficients using the Darken equation agree well with experimental data in the literature.     

d Band structure and alloying effects in crystalline and amorphous ZrCo and ZrNi

We study the electronic structure by photoemission of amorphous Zr₇₀Co₃₀, Zr₇₅ Ni₂₅ and crystalline Zr₂Co, Zr₂Ni. The results show that the electronic structures for the amorphous and crystalline states are quite similar. The valence bands of the amorphous alloys do not present features attributable specifically to the amorphous state. In both cases the valence band indicate a strong localization of the d levels and can be interpreted as a superposition of the Zr 4d levels in the upper part of the band, the Co or Ni 3d levels being centered in the low part of the part of the band. The present results and previous ones on ZrCu amorphous alloys show that the binding energies of the 3d levels increase with the distance between the alloying elements in the periodic table. Moreover the full width at half maximum of Co, Ni or Cu d levels is noticeably less than for pure elements. These results are considered at the light of atomic structure and theoretical models ; in particular it seems that the coordination number of the atoms plays a dominant role in the structure of the d levels.     

Ab initio molecular-dynamics simulations of short-range order in liquid Al80Mn20 and Al80Ni20 alloys

Atomic structures of liquid Al80Mn20 and Al80Ni20 have been calculated by first-principles molecular-dynamics simulations. For both liquid alloys, the local structure is characterized by a strong Al-TM (transition metal) affinity, which leads to a well-pronounced chemical short-range order. However, we show that the occurrence of magnetic moments localized on Mn atoms plays a key role in determining the short-range arrangement of Mn atoms which is also interpreted on the basis of the local fivefold symmetry.     

Phase segregation and crystallization in the amorphous alloy Ni70Mo10P20

Structural evolution of the amorphous alloy Ni₇₀Mo₁₀P₂₀ has been studied by x-ray diffraction, and by following transmission and high-resolution electron microscopy annealing both above and below the glass-transition temperature. When annealed above this temperature, the amorphous phase undergoes segregation into regions about 100 nm in size having different chemical composition. Diffraction from such samples produces diffuse rings, and the scattering vector corresponding to the maximum intensity varies from point to point within the interval of 4.88 to 4.78 nm⁻¹. When occurring between the glass-transition and crystallization temperatures, crystallization produces groups of nanocrystals, 20–30 nm in size, which are in direct contact with one another and form a polymorphic mechanism. The crystallization mechanism changes when the annealing temperature is brought below the glass-transition point. At these temperatures the amorphous matrix crystallizes entectically with formation of eutectic colonies. Fiz. Tverd. Tela (St. Petersburg) 40, 1577–1580 (September 1998)     

压力对Zr46.75Ti8.25 Cu7.5Ni10Be27.5大块非晶合金玻璃转变和晶化动力学的影响

利用X射线衍射和差示扫描量热分析研究了高温高压下Zr46.75Ti8.25Cu7.5Ni10Be27.5大块非晶合金的玻璃转变和晶化行为,结果发现压力降低了该大块非晶合金中的自由体积、热焓和晶化激活能.     

超细Ni80Cr20合金丝的冷拉拔制备及表征

开展特定直径超细Ni80Cr20合金丝的冷拉拔制备研究,并通过扫描电子显微镜（SEM）、X射线衍射仪（XRD）和金属丝强力仪等对超细合金丝进行了表征。研究结果表明：烧头过程最佳电解液浓度为0.05 mol/L,时间为3 s;制备的镍铬合金丝直径为24.54 m,表面光滑,尺寸精准;拉拔后晶粒尺寸减小,退火后晶粒尺寸长大;拉拔态镍铬丝由于加工硬化,其伸长率由16%降低至1.88%;退火可改善镍铬丝性能,其断裂强度降低,伸长率增大,合金塑性增强,氮气退火丝的断裂强度大于真空退火丝的断裂强度,伸长率则相反。