Effect of nanocrystallization on the mechanical and magnetic properties of finemet-type alloy (Fe<Subscript>78.5</Subscript>Si<Subscript>13.5</Subscript>B<Subscript>9</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript>)

The kinetics of primary crystallization and the effect of structural parameters of the precipitating nanocrystalline α-phase Fe-Si on changes in microhardness, coercive force, and saturation magnetization in an amorphous Finemet-type 5BDSR alloy (Fe_78.5Si_13.5B₉Nb₃Cu₁) obtained by melt quenching are studied. It is found that both an increase in bulk density and an increase in the average nanoparticle size contribute to the hardening of the amorphous/nanocrystalline alloy.     

Formation and structure of nanocrystals in bulk Zr<Subscript>50</Subscript>Ti<Subscript>16</Subscript>Cu<Subscript>15</Subscript>Ni<Subscript>19</Subscript> metallic glass

The possible formation of a nanocrystalline structure in controlled crystallization of a bulk Zr₅₀Ti₁₆Cu₁₅Ni₁₉ amorphous alloy has been studied using differential scanning calorimetry, transmission and high-resolution electron microscopy, and x-ray diffraction. It was established that crystallization of the alloy at temperatures above the glass formation point occurs in two stages and brings about the formation of a nanocrystalline structure consisting of three phases. Local spectral x-ray analysis identified the composition and structure of the phases formed.     

Dependence of the optical properties of Fe<Subscript>78</Subscript>Si<Subscript>10</Subscript>B<Subscript>12</Subscript> amorphous alloy on its structural state

The optical properties of Fe₇₈Si₁₀B₁₂ ferromagnetic alloy in amorphous, crystalline, and intermediate structural states have been investigated by ellipsometry in the spectral range of 0.22–18 μm. It is established that alloy crystallization leads to a significant change in the optical constants and the frequency dependences of the dielectric functions calculated based on these optical constants. The structural reconstruction under heat treatment leads to an increase in the intensity and shift of interband absorption bands. The plasma and relaxation frequencies of conduction electrons are determined; their numerical values also depend on the degree of atomic ordering.     

Specific heat and electrical resistivity of an icosahedral-structure Zr<Subscript>70</Subscript>Pd<Subscript>30</Subscript> alloy and of its amorphous and crystalline analogs

Binary icosahedral and crystalline phases of the Zr₇₀Pd₃₀ alloy were obtained in crystallization from the amorphous state during heat treatment. The specific heat and electrical resistivity of the icosahedral, amorphous, and crystalline phases were measured and compared. An increase in the electronic density of states on the Fermi surface, lattice softening, and an increase in the electron-phonon coupling constant were observed to occur with decreasing structural order. Despite the high valence electron density in the icosahedral phase, where the electronic densities of states are twice those in the crystal, the electrical resistivity of the icosahedral phase is ～50 times as high. Superconductivity was observed for the first time in the icosahedral phase of a binary system of transition metal atoms, Zr₇₀Pd₃₀.     

Crystallization kinetics of Al<Subscript>86</Subscript>Ni<Subscript>8</Subscript>Ho<Subscript>6</Subscript> amorphous alloy

We investigate the processes of crystallization and determined the structure and thermal properties of Al₈₆Ni₈Ho₆ amorphous alloy in a wide temperature range. A three-stage nature of the crystallization process upon heating to a temperature of 700 K is found. According to data of high-temperature X-ray diffraction analysis, the crystallization of an Al₈₆Ni₈Ho₆ amorphous ribbon is rather complex: aluminum crystallites grow in the amorphous phase to a temperature of 470 K, a Ho₃Ni₅Al₁₉ phase is formed above 563 K, and a HoAl₃ phase appears above 598 K. The phases of Ho₃Ni₅Al₁₉ and HoAl₃ are retained up to a temperature of 723 K. A three-stage kinetic model of the crystallization process with the reaction sequence is proposed based on calculations by multivariate nonlinear regression. The values of the total activation energy for each crystallization stage reach 239, 378, and 247 kJ/mol.     

Nanocrystallization of an amorphous Fe<Subscript>80</Subscript>B<Subscript>20</Subscript> alloy during severe plastic deformation

The structural evolution of an amorphous Fe₈₀B₂₀ alloy subjected to severe plastic deformation at room temperature or at 200°C was studied. Deformation leads to the formation of α-Fe nanocrystals in an amorphous phase. After room-temperature deformation, nanocrystals are localized in shear bands. After deformation at 200°C, the nanocrystal distribution over the alloy is more uniform. Possible causes of the crystallization of the amorphous phase during severe plastic deformation are discussed.     

Structural transformations in the Al<Subscript>85</Subscript>Ni<Subscript>6.1</Subscript>Co<Subscript>2</Subscript>Gd<Subscript>6</Subscript>Si<Subscript>0.9</Subscript> amorphous alloy during multiple rolling

The effect of multiple rolling at room temperature on the structure and crystallization of the Al₈₅Ni_6.1Co₂Gd₆Si_0.9 amorphous alloy has been studied using transmission electron microscopy, differential scanning calorimetry, and X-ray diffraction. The total plastic strain is 33%. It has been shown that the deformation results in the formation of aluminum nanocrystals with the average size that does not exceed 10–15 nm. The nanocrystals are formed in regions of localization of plastic deformation. The deformation decreases the thermal effect of nanocrystallization (∼15%) as compared to the heat release at the first stage of crystallization of the unstrained sample. The morphology, structure, and distribution of precipitates have been investigated. Possible mechanisms of the formation of nanocrystals during the deformation have been discussed.     

Magnetic and Mössbauer Studies of Fe<Subscript>76</Subscript>Mo<Subscript>8</Subscript>Cu<Subscript>1</Subscript>B<Subscript>15</Subscript> Nanocrystalline Alloy

The influence of different degrees of crystallinity on the magnetic behaviour of heat-treated nanocrystalline Fe₇₆Mo₈Cu₁B₁₅ alloy has been investigated using a combination of Mössbauer spectrometry and magnetic measurements. The evolution of magnetically active regions and their growth with rising contents of nanocrystals are followed by distributions of hyperfine interactions. Combined electric quadrupole and magnetic dipole interactions corresponding to non-magnetic and magnetic regions inside the amorphous phase, respectively, were revealed. A deterioration of the soft-magnetic properties takes place for the samples exhibiting low fraction of crystallinity. The very good soft-magnetic behaviour is regained for the samples where the primary crystallization process is almost finished.     

Influence of deformation on the structural transformation of the Pd<Subscript>40</Subscript>Ni<Subscript>40</Subscript>P<Subscript>20</Subscript> amorphous phase

The influence of plastic deformation on the structure of the Pd₄₀Ni₄₀P₂₀ amorphous alloy has been investigated using X-ray diffraction and measurements of the velocity of sound. It has been revealed that the rolling of the sample leads to a change in the structure of the amorphous phase (distortion of the first coordination sphere) and that the structural transformations are more pronounced in the near-surface region of the sample. The rolling also results in a decrease in the transverse velocity of sound. The observed effects decrease with time. It has been demonstrated that the revealed effects are associated with the inelastic deformation of the amorphous alloy.     

Electron microscopic investigation of the kinetics of the layer and island crystallization of amorphous V<Subscript>2</Subscript>O<Subscript>3</Subscript> films deposited by pulsed laser evaporation

An electron microscopic investigation was performed on the kinetics of the layer and island crystallization of amorphous V₂O₃ films deposited by pulsed laser evaporation of vanadium in an oxygen atmosphere. The crystallization was initiated by the action of an electron beam on an amorphous film in the column of a transmission electron microscope. The kinetic curves were plotted on the basis of a frame-by-frame analysis of the video recorded during the crystallization of the film. It was found that the layer crystallization of amorphous films is characterized by a quadratic dependence of the fraction of the crystalline phase x on the time t, whereas the island crystallization is described by an exponential dependence of x on t. The kinetic curves of island crystallization of amorphous films were analyzed on the basis of the α-version of the Kolmogorov model. For each type of crystallization, there are specific values of the dimensionless relative length unit δ₀, which is equal to the ratio of the characteristic length unit to the parameter characterizing the unit cell of the crystal. It was established that, for the layer crystallization, the relative length unit lies in the range δ₀ ~ 4300–4700, whereas for the fine-grained island crystallization, it amounts to δ₀ ~ 110.     

Anomalous magnetoresistivity of the superconducting Zr<Subscript>80</Subscript>Pt<Subscript>20</Subscript> system in quasicrystalline and amorphous states

The binary icosahedral Zr₈₀Pt₂₀ system has been synthesized during the crystallization of an initially amorphous alloy fabricated by melt quenching on the surface of a rotating copper wheel. The temperature and field dependences of the electrical resistivity and magnetoresistivity of the icosahedral and amorphous phases are studied and compared in a temperature range of 1.5–300 K and magnetic fields up to 8 T. Superconductivity has been detected for the first time in the icosahedral and amorphous phases of the Zr₈₀Pt₂₀ system. For both phases, the magnetoresistivity is positive and depends anomalously on the magnetic field. The anomalous behavior of magnetoresistivity is satisfactorily described by the theory of weak localization and electron-electron interaction in three-dimensional disordered systems, which takes into account electron scattering by superconducting fluctuations. The absolute values and temperature dependences of the electron-electron interaction constant and the times of inelastic scattering of conduction electrons are estimated for the icosahedral and amorphous phases of this binary system.     

<Emphasis Type="Italic">In situ</Emphasis> X-ray diffraction study of structural evaluation in Fe<Subscript>73</Subscript>Cu<Subscript>1.5</Subscript>Nd<Subscript>3</Subscript>Si<Subscript>13.5</Subscript>B<Subscript>9</Subscript> amorphous alloy at high temperature

The thermodynamics structural relaxation of Fe₇₃Cu_1.5Nd₃Si_13.5B₉ amorphous alloy from room temperature to 400°C has been investigated by measuring the structure factor with in situ X-ray diffraction. The structural information of the atomic configuration such as radial distribution function (RDF) and neighbor atomic distance was gained by Fourier transformation. The research result shows that the amorphous structure remains stable in the temperature range of 30 to 400°C but exhibits distinct changes in local atomic configuration with the increase of temperature. The quantitative determination of the neighbor atomic distance suggests that the degree of short-range order changes by the temperature altering the second nearest neighbor local atomic configuration of the amorphous when structural relaxation occurs. Supported by the Natural Science Foundation of Hebei Province of China (Grant No. A2007000296), the National Natural Science Foundation of China (Grant No. 50731005), SKPBRC (Grant Nos. 2007CB616915 and 2006CB605201), and PCSIRT (Grant No. IRT0650)     

Features of the formation of an oxide layer on the surface of amorphous Zr<Subscript>41.2</Subscript>Ti<Subscript>13.8</Subscript>Cu<Subscript>12.5</Subscript>Ni<Subscript>10.0</Subscript>Be<Subscript>22.5</Subscript> alloy

Field investigations were performed into the nature of oxidation of Zr_41.2Ti_13.8Cu_12.5Ni_10.0Be_22.5 alloy (Vitreloy-1), a new alloy highly promising for in -vessel mirrors of the ITER (International Thermonuclear Experimental Reactor). The main methods of investigation were X-ray photoelectron spectroscopy and multi-angle ellipsometry. The resistance of the optical properties of Vitreloy-1 against radiation impact was explained by the oxidation of the surface layer, based on the features of the diffusion process in amorphous alloys and of interaction between amorphous metal alloys with hydrogen.     

Mechanical alloying of Ni<Subscript>80</Subscript>Ta<Subscript>20</Subscript> and Ni<Subscript>80</Subscript>Nb<Subscript>20</Subscript>. Crystallization of the amorphous phase

The sequence and crystallization kinetics of the amorphous phase have been analyzed by differential scanning calorimetry and X-ray diffraction for mechanochemically activated Ni₈₀Ta₂₀ and Ni₈₀Nb₂₀ samples. The formation of equilibrium products from the amorphous phase occurs through the formation of metastable products of the A3 type. The kinetic parameters (activation energy and reaction order) and thermodynamic characteristics of this process are determined. Crystallization of the amorphous phase for the Ni₈₀Ta₂₀ and Ni₈₀Nb₂₀ systems occurs due to the growth of existing nuclei through the polymorphic and eutectic mechanisms, respectively. The thermal effects of the synthesis of equilibrium products from a mechanochemically activated mixture of components are identified.     

Atomic and magnetic structures of Fe<Subscript>70</Subscript>Al<Subscript>5</Subscript>B<Subscript>25</Subscript> amorphous alloys

The short-range order around boron, aluminum, and iron atoms in Fe₇₅B₂₅ and Fe₇₀Al₅B₂₅ amorphous alloys has been studied by ¹¹B and ²⁷Al nuclear magnetic resonance at 4.2 K and ⁵⁷Fe Mössbauer spectroscopy at 87 and 295 K. The average magnetic moment of iron atoms μ(Fe) in these alloys has been measured by a vibrating sample magnetometer. It has been revealed that the substitution of aluminum atoms for iron atoms does not disturb μ(Fe) in the Fe₇₀Al₅B₂₅ alloy, gives rise to an additional contribution to the ¹¹B NMR spectrum in the low-frequency range, and shifts maxima of the distribution of hyperfine fields at the ⁵⁷Fe nuclei. In the Fe₇₀Al₅B₂₅ amorphous alloy, the aluminum atoms substitute for iron atoms in the nearest coordination shells of boron and iron atoms. This alloy consists of nanoclusters in which boron and iron atoms have a short-range order of the tetragonal Fe₃B phase type.     

Glass-forming ability and thermal stability of Fe<Subscript>62</Subscript>Nb<Subscript>8−x</Subscript>Zr<Subscript>x</Subscript>B<Subscript>30</Subscript> and Fe<Subscript>72</Subscript>Zr<Subscript>8</Subscript>B<Subscript>20</Subscript> amorphous alloys?

Glass-forming ability (GFA) and thermal stability of Fe₆₂Nb₈B₃₀, Fe₆₂Nb₆Zr₂B₃₀ and Fe₇₂Zr₈B₂₀ at % amorphous alloys were investigated by calorimetric (DSC and DTA) measurements. The crystallization kinetics was studied by DSC in the mode of continuous versus linear heating and it was found that both the glass transition temperature, T _g , and the crystallization peak temperature, T _p , display strong dependence on the heating rate. The partial replacement of Nb by Zr leads to lower T _g and T _x temperatures and causes a decrease of the supercooled liquid region. JMA analysis of isothermal transformation data measured between T _g and T _x suggests that the crystallization of the Fe₆₂Nb₈B₃₀ and Fe₆₂Nb₆Zr₂B₃₀ amorphous alloys take place by three-dimensional growth with constant nucleation rate. Nb enhances the precipitation of the metastable Fe₂₃B₆ phase and stabilizes it up to the third crystallization stage. Zr addition increases the lattice constant of Fe₂₃B₆ and, at the same time, decreases the grain size.     

Serrated deformation of a Pd<Subscript>40</Subscript>Cu<Subscript>30</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript> bulk amorphous alloy during nanoindentation

Depth-sensing (indentation) testing is used to study the characteristics of a serrated plastic flow in a Pd₄₀Cu₃₀Ni₁₀P₂₀ bulk amorphous alloy, and the boundaries between the regions of serrated and homogeneous plastic deformation are determined.     

Molecular-dynamics study of the Ni<Subscript>60</Subscript>Ag<Subscript>40</Subscript> binary alloy glass transition

Features in the evolution of the atomic structure of the Ni₆₀Ag₄₀ alloy upon quenching from a liquid disordered state were revealed within the molecular-dynamics method using many-particle potentials of interatomic interaction, calculated within the embedded atom method. It was shown that the structural stabilization of the amorphous Ni₆₀Ag₄₀ phase during the glass transition occurs due to the formation of a percolation cluster of interpenetrating and contacting icosahedra with nickel and silver atoms at vertices and preferentially nickel atoms at centers.     

Magnetic and Mössbauer Studies of Fe<Subscript>76</Subscript>Mo<Subscript>8</Subscript>Cu<Subscript>1</Subscript>B<Subscript>15</Subscript> Amorphous Alloy

“Zero field”-Mössbauer and magnetization measurements have been performed on an amorphous Fe₇₆Mo₈Cu₁B₁₅ alloy in the temperature range of (10-340) K. The room-temperature Mössbauer spectrum exhibits magnetic dipole and electric quadrupole interactions. At approximately 306 K, the magnetic interactions vanish and the alloy shows fully paramagnetic behavior. On the other hand, the relative representation of paramagnetic component becomes weak with decreasing temperature and below 220 K the magnetic dipole interactions prevail. Below this temperature an anomaly in the low-temperature dependencies of ac susceptibility and of magnetization, measured during cooling the specimen from 340 K down to 20 K is observed. The anomaly on the magnetization curve vanishes in the field of 200 Oe.     

Magnetic properties and the magnetoimpedance effect of nanostructured Fe<Subscript>73.5</Subscript>Si<Subscript>16.5</Subscript>B<Subscript>6</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript> ribbons with induced magnetic anisotropy

The structure and magnetic properties and the magnetoimpedance effect of nanocrystalline Fe_73.5Si_16.5B₆Nb₃Cu₁ alloy ribbons, obtained from the amorphous state by annealing under different conditions, were comparatively analyzed. Despite the similarity of the samples’ structural states and the processes of their quasi-static magnetization reversal, the features of the magnetoimpedance effect are indicative of significant differences in the processes of their dynamic magnetization.