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.     

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.     

Stress relaxation in an Zr<Subscript>52.5</Subscript>Ti<Subscript>5</Subscript>Cu<Subscript>17.9</Subscript>Ni<Subscript>14.6</Subscript>Al<Subscript>10</Subscript> bulk metallic glass

The isothermal relaxation of stresses in a bulk metallic glass is measured at temperatures below the glass transition point. The kinetic law of relaxation is determined. It is argued that the stress relaxation in the temperature range covered is due to the irreversible structural relaxation oriented by an external stress and characterized by a distribution of activation energies.     

Higher order elastic moduli of the bulk metallic glass Zr<Subscript>52.5</Subscript>Ti<Subscript>5</Subscript>Cu<Subscript>17.9</Subscript>Ni<Subscript>14.6</Subscript>Al<Subscript>10</Subscript>

The effect of elastic loading on the velocity of propagation of acoustic waves in a solid is calculated (to the second order in the applied load). The results of the calculations and the experimental data on the effect of uniaxial loading on the propagation of ultrasonic waves in the bulk metallic glass Zr_52.5Ti₅Cu_17.9Ni_14.6Al₁₀ are used to estimate the third-order and fourth-order elastic moduli.     

Microstructure of Cu<Subscript>60</Subscript>Zr<Subscript>20</Subscript>Ti<Subscript>20</Subscript> bulk metallic glass rolled at different strain rates

The structural evolution of Cu₆₀Zr₂₀Ti₂₀ bulk metallic glass during rolling at different strain rates and cryogenic temperature was investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy (HRTEM). It is revealed that the deformation-induced transformation is strongly dependent on the strain rate. At the lowest experimental strain rate of 1.0×10⁻⁴ s⁻¹, no phase transformation occurs until the highest deformation degree reaches 95%. In a strain rate range of 5.0×10⁻⁴−5.0×10⁻² s⁻¹, phase separation occurs in a high deformation degree. As the strain rate reaches 5.0×10⁻¹ s⁻¹, phase separation and nanocrystallization concur. The critical deformation degree for occurrence of phase transformation decreases with the strain rate increasing. Supported by the National Natural Science Foundation of China (Grant No. 50471016)     

Compression behavior of Zr<Subscript>41</Subscript>Ti<Subscript>14</Subscript>Cu<Subscript>12.5</Subscript>Ni<Subscript>10</Subscript>Be<Subscript>22.5</Subscript> bulk metallic glass up to 24 GPa

The compression of a Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk metallic glass (BMG) is investigated at room temperature up to 24 GPa using in-situ high pressure energy dispersive X-ray diffraction with a synchrotron radiation source. The pressure-induced structural relaxation is exhibited. It is found that below about 8 GPa, the existence of excess free volume contributes to the rapid structural relaxation, which gives rise to the rapid volumetric change, and the structural relaxation results in the structural stiffness under higher pressure.     

Structural relaxation of Zr<Subscript>41</Subscript>Ti<Subscript>14</Subscript>Cu<Subscript>12.5</Subscript>Ni<Subscript>10</Subscript>Be<Subscript>22.5</Subscript> bulk metallic glass under high pressure

Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk metallic glass (BMG) is annealed at 573 K under 3 GPa and its structural relaxation is investigated by X-ray diffraction, ultrasonic study, compression as well as sliding wear measurements. It is found that after the ZrTiCuNiBe BMG sample was annealed under high pressure, the mechanical properties were improved. Moreover, theBMG with relaxed structure exhibits markedly different acoustic properties. These results are attributed to the fact that relaxation under high-pressure results in a microstructural transformation in the BMG.     

Effect of heat treatment on the structure and elastic properties of a bulk Pd<Subscript>40</Subscript>Cu<Subscript>30</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript> metallic glass

The effect of heat treatment over the range from room temperature to 500°C on the elastic properties of a bulk amorphous Pd₄₀Cu₃₀Ni₁₀P₂₀ alloy was studied. It is shown that the increase in the shear modulus under crystallization of the alloy is two-staged and that the most significant increase in the modulus occurs at the second stage. The obtained results are compared to the x-ray structural data. It is also found that the density characteristics of the as-cast material change very slightly during the transformation from the amorphous to the crystal state, with the density decreasing slightly due to crystallization.     

Phase transition in Pd<Subscript>40</Subscript>Ni<Subscript>10</Subscript>Cu<Subscript>30</Subscript>P<Subscript>20</Subscript> bulk metallic glass under HP &; HT

The phase transitions in Pd₄₀Ni₁₀Cu₃₀P₂₀ bulk metallic glass (BMG) have been studied under high pressure and high temperature (HP & HT) by X-ray diffaction measurements with synchrotron radiation source. We found that the BMG underwent a phase transitions of amorphous-crystalline-amorphous at 10 GPa upon heating. The parallel experiments were carried out at 7 GPa, while we did not observe the amorphous-crystalline-amorphous transitions by increasing temperature. Quenching the melted BMG at 7 GPa, it was found that the phase crystallized from the melt differed from the primary phase crystallized from the starting amorphous solid upon heating suggesting there existed a distinct mechanism in two cases.     

Recovery of electrical-resistivity and viscoelasticity relaxation in thermally aged bulk Pd<Subscript>40</Subscript>Cu<Subscript>30</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript> metallic glass

The structural relaxation of a bulk Pd₄₀Cu₃₀Ni₁₀P₂₀ metallic glass is studied by measuring the electrical resistivity and infralow-frequency (0.05 Hz) internal friction. It is demonstrated that the structural relaxation in thermally aged samples can be restored by quenching them from a supercooled liquid state. It is found that the degree of relaxation after quenching can exceed the initial one by several times.     

Stress relaxation and viscosity of a bulk Pd<Subscript>40</Subscript>Cu<Subscript>30</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript> metallic glass under isochronous heating conditions

Isochronous relaxation of tensile stresses is measured in a bulk Pd₄₀Cu₃₀Ni₁₀P₂₀ metallic glass in the initial state and after certain thermal treatments. The results of measurements are used to find the energy spectrum of irreversible structural relaxation, from which the temperature dependence of shear viscosity is then calculated. This dependence is also found independently from measurements of creep in the same glass. The calculated viscosity is shown to agree well with the experimental data.     

Search for acoustic and optic vibrational modes in Zr<Subscript>40</Subscript>Be<Subscript>60</Subscript> metallic glass

Dispersion of collective modes in metallic glass (Zr₄₀Be₆₀, composed of disparate mass particles) was measured at small-angle spectrometer BRISP at the ILL what enabled us to extend to lower momentum transfers unlike to high-angle spectrometer IN4 at the ILL. It was shown that the behavior of the optical mode in the metallic glass is similar to the behavior of optic modes in the other systems with non-sized atoms (liquid LiPb, inert gas mixtures with high density (He₆₅Ne₃₅)).     

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.     

Thermal stability of microstructures and mechanical properties in a Fe-based Fe-Cr-Mn-Cu-Mo multi-component alloy

A Fe-based multi-component alloy, 60Fe-12Cr-10Mn-15Cu-3Mo, was designed and fabricated for nuclear applications in the present study. The crystal structure of the alloy is a ～85% body – and 15% face–centered cubic. A detailed microstructure analysis indicated that Cu segregated in the alloy to form Cu-rich precipitates, and the Cu precipitates grew during high temperature annealing at up to 773?K. The high temperature tensile test of the alloys showed that both the yield stress and tensile strength of the 60Fe-12Cr-10Mn-15Cu-3Mo were greater than those of typical austenitic and ferritic stainless steels at 773?K. The Vickers microhardness of the designed alloy did not change after high temperature annealing for 1?h at up to 1073?K. The results indicated that the designed alloy has the potential to be used for high temperature applications.     

Recovery of viscoelasticity in aged metal glass Pd<Subscript>40</Subscript>Cu<Subscript>30</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript>

It is established that quenching of an aged metal glass from the supercooled liquid state causes recovery of its viscoelastic properties, which manifest themselves in measurements of the infralow-frequency internal friction.     

Shear viscosity of the Pd<Subscript>40</Subscript>Cu<Subscript>40</Subscript>P<Subscript>20</Subscript> metallic glass under conditions of isochronous heating below the glass transition temperature

The shear viscosity is measured under conditions of isochronous (linear) heating below the glass transition temperature of the Pd₄₀Cu₄₀P₂₀ metallic glass, which is characterized by the polymorphic crystallization into the Pd₂Cu₂P tetragonal phase with a lower density than the initial glass. It is shown that the rate dependence of the shear viscosity can be interpreted as a result of the irreversible structural relaxation by analogy with the case of the previously studied metallic glasses despite the unusual ratio of the densities of the material in noncrystalline and crystalline states.     

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.     

Isothermal kinetics and relaxation recovery of high-frequency shear modulus in the course of structural relaxation of Pd<Subscript>40</Subscript>Cu<Subscript>30</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript> bulk glass

Isothermal kinetics of relaxation of the high-frequency (1.4 MHz) shear modulus during structural relaxation of Pd₄₀Cu₃₀Ni₁₀P₂₀ bulk metallic glass below the glass transition temperature is studied by an in situ method of contactless electromagnetic acoustic transformation. The kinetic law of relaxation is established. It is shown that quenching of aged samples from the supercooled liquid state leads to a decrease in the absolute value of shear modulus to below the initial value; the degree of subsequent isothermal relaxation of the modulus may be several times higher than the initial value. Possible reasons for relaxation and recovery of the shear modulus are considered.     

Ordering,martensitic transformation,and shape memory effect in submicron samples of rapidly quenched Ni<Subscript>50</Subscript>Ti<Subscript>25</Subscript>Cu<Subscript>25</Subscript> alloy

The experiments aimed at developing micro- and nanomechanical devices based on shape memory alloys are described. A novel scheme and a model of microtweezers for manipulating nanoobjects with extremely small sizes (12 × 3 × 1 μm³) are proposed. The control of microtweezers deformation by local heating is demonstrated. The controlled cantilever bending was found to be 1000 nm; this value is in good agreement with the theoretical data.     

Vibrational and electronic properties of the amorphous systems Ni<Subscript>44</Subscript>Nb<Subscript>56</Subscript>, Ni<Subscript>62</Subscript>Nb<Subscript>38</Subscript>, and Cu<Subscript>33</Subscript>Zr<Subscript>67</Subscript> as derived from specific heat measurements

The specific heats of the amorphous systems Ni₄₄Nb₅₆, Ni₆₂Nb₃₈, and Cu₃₃Zr₆₇ were studied in the temperature range 3–273 K. The data obtained allow one to isolate the contribution due to atomic vibrations from the experimentally measured specific heat, to determine the density of electronic states at the Fermi level and the temperature dependence of the characteristic Debye parameter Θ over a broad temperature range, and to calculate a few frequency moments that characterize the vibrational spectrum. The information derived on the average characteristics of vibrational spectra is in good agreement with earlier data on inelastic neutron scattering. In transferring from Ni₄₄Nb₅₆ to Ni₆₂Nb₃₈, the density of electronic states at the Fermi level decreases and the characteristic vibrational frequencies increase. The density of electronic states at the Fermi level for Cu₃₃Zr₆₇ is close to that for Ni₆₂Nb₃₈. The characteristic frequencies of the vibrational spectrum of the Cu₃₃Zr₆₇ system are substantially lower (by 30%) than those of the Ni₄₄Nb₅₆ and Ni₆₂Nb₃₈ systems.