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.     

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.     

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.     

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.     

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 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.     

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.     

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.     

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.     

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.     

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 plastic deformation on the electronic properties of the Cu<Subscript>60</Subscript>Pd<Subscript>40</Subscript> alloy

The effect of severe plastic deformation by torsion under Bridgman anvil pressure (SPDT) on the electrical, magnetic, and optical properties of the Cu₆₀Pd₄₀ alloy was studied. It is shown that, after the alloy is disordered, the Curie-Weiss constants of the paramagnetic component are changed insignificantly. In this case, the temperature-independent negative component of the magnetic susceptibility decreases more than fivefold. The electrical resistance and negative thermopower, on the contrary, increase severalfold as a result of SPDT. The character of the optical conductivity is discussed using the band structure calculation results.     

A simulation study of rapid solidification and crystal configuration of Cu<Subscript>70</Subscript>Ni<Subscript>30</Subscript> alloy

A molecular dynamics (MD) simulation study has been performed for the rapid solidification of Cu₇₀Ni₃₀ adopting the quantum Sutton-Chen many-body potentials. By analyzing the bond-types and the relation of atomic average energy versus temperature, it was demonstrated that as cooling rate being 2×10¹² K/s, the Cu₇₀Ni₃₀ formed fcc crystal structures and freezing point was found. In addition, having analyzed the transformation of microstructures and the detail of crystal growth by using atomic trace and visual method, not only could the formation of binary disordered solid solution be showed, but also the solidification of liquid metals and the crystal growth processes could be, further understood.     

Formation,thermal stability and mechanical properties of Ti<Subscript>42.5</Subscript>Zr<Subscript>7.5</Subscript>Cu<Subscript>40</Subscript>Ni<Subscript>5</Subscript>Sn<Subscript>5</Subscript> bulk metallic glass

Ti_42.5Zr_7.5Cu₄₀Ni₅Sn₅ bulk metallic glass with a critical diameter of 4 mm was fabricated by the conventional copper mould casting method. The supercooled liquid region ΔT _x, reduced glass transition temperature T _rg, γ parameter, and δ parameter of the alloy were measured to be 63.9 K, 0.561, 0.393, and 1.400, respectively, implying that the alloy has an excellent glass-forming ability. The bulk metallic glass exhibits high compressive fracture strength of 2162 MPa with distinct plastic strain of 0.9%. The fracture surface consists mainly of vein-like patterns, typical of bulk glassy alloys. Supported by the Program for New Century Excellent Talents in University of China and the National Natural Science Foundation of China (NSFC)(Grant No. 50771040)     

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.     

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.     

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.     

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)     

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.     

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.