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.     

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.     

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.     

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.     

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.     

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.     

Kinetics of structural relaxation of bulk and ribbon Pd<Subscript>40</Subscript>Cu<Subscript>30</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript> glasses determined from electrical resistance measurements

The electrical resistances of ribbon and bulk Pd₄₀Cu₃₀Ni₁₀P₂₀ metallic glasses, whose quenching rates differ by four orders of magnitude, were precisely measured during cyclic heating. Three stages of electrical resistance relaxation are detected as the maximum heating temperature increases. The first and third stages decrease the electrical resistance, and the second stage increases it. The first stage is shown to be caused by the relaxation of deformation-induced internal stresses and not to be related to the excess free volume concentration, which differs by a factor of about 2 in the ribbon and bulk samples. The second stage reflects structural relaxation in the glass and is only partly related to its free volume. The third relaxation stage is assumed to be caused by fine precrystallization phenomena like phase separation. The effect of deformation by rolling or quenching from the temperature range of a supercooled melt on the resistance relaxation kinetics was also studied.     

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.     

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.     

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.     

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)     

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.     

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,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)     

Structural organization in the Cu<Subscript>80</Subscript>Zr<Subscript>20</Subscript> metallic glass

The laws of atomic restructuring in the Cu₈₀Zr₂₀ metallic glass during melt quenching are studied by molecular dynamics simulation using statistical-geometrical analysis based on Voronoi polyhedra and cluster analysis. The morphology and size distribution of polyhedral nanoclusters in the glass structure are investigated.     

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.     

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.