In the present work, the influence of Co addition on the glass forming ability (GFA) and magnetic properties of the ((Fe1−xCox)75B20Si5)93Nb4Y3 (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1) alloy is evaluated. Ribbons and 1 mm diameter ingots were prepared by melt-spinning technique and Cu-mold injection casting technique, respectively. The presence of the amorphous phase was confirmed through X-ray diffraction and high temperature differential scanning calorimetry (HT-DSC). Rapid solidification leads to fully amorphous ribbons for all compositions. Conversely, ingots with Co content with x > 0.5 present boride crystalline phases.

Magnetization measurements were performed by means of vibration sample magnetometer in a temperature range from room temperature to 850 °C in order to determine the Curie temperature (TC) of the amorphous phase and to follow the formation of magnetic phases at high temperatures. In addition, hysteresis loops measurements were carried out to study the magnetic response of the samples. Co substitution until x = 0.5 is seen to simultaneously induce in the as cast ingots a decrease of coercive field from 52 to around 10 A/m and an increase of the Curie temperature of the amorphous phase from 480 to 700 K. A maximum saturation magnetization value of 123 emu/g was observed in the sample having x = 0.2. The role of Co substitution on glass formation is discussed on the basis of crystallization and melting behaviors, analyzed by HT-DSC. Magnetic properties are correlated with the presence of crystalline phases and their microstructures.

The problem of structural properties and structural defects of amorphous solids is still of vital importance. To make clear whether stable point defects exist in metallic glasses (MGs) or not, we have studied the accumulation and recovery kinetics of radiation defects in ZrTiCuNiBe and ZrTiCuNiAl bulk MGs irradiated with 2.5 MeV electrons at T ∼ 80 K. The electrical resistance measurements of the irradiated samples were performed. The recovery spectrum of irradiation-induced electrical resistance was measured for the 85–300 K temperature range. The most important result of the recovery experiments is that they clearly show the annealing stages for the irradiated samples. Two annealing peaks located at T∼150 K and T∼225 K are resolved for ZrTiCuNiBe glass. Similar peaks are also revealed for ZrTiCuNiAl. It can be concluded from the data that the defect mobility is a thermally activated process, and that the activation energy is not as high as that for vacancies in crystalline alloys. Thus, the data obtained testify in favor of the structure with “perfect” local ordering of atoms. It should be noted that this property is basic in the formulation of the polycluster model of amorphous solids.

The deformation and damage evolution behavior of a Ni-based bulk metallic glass composite reinforced with elongated brass phase is studied under cylindrical indentation. The estimated fracture toughness values based on the energy dissipation and the in-situ observation during the loading reveal the details of the damage evolution and toughening mechanisms in this composite system. The results indicate that the enhanced toughness of the BMG composite is plausibly an outcome of crack bridging mechanisms by the ductile brass phase, rather than a diffused array of nucleated shear bands in the hard BMG and arrest by the ductile reinforcing phase.

Electron irradiation induced phase transition behavior of Zr-Pd and Zr-Pt alloys was investigated focusing on phase selection in crystallization by thermal annealing and electron irradiation. Nano quasi-crystalline (QC) phase was formed by thermal crystallization in Zr66.7Pd33.3 and Zr80Pt20 alloys, while nano two-type f.c.c. super-saturated solid solutions were formed by irradiation induced crystallization at 298K. In Zr66.7Pt33.3 alloy, polycrystalline Zr5Pt3 and Zr9Pt11 phases transformed to two-type f.c.c. nano-crystalline phase through an amorphous state by crystal-to-amorphous-to-crystal (C-A-C) transition during electron irradiation. Nano-composite phase composed of f.c.c. super-saturated solid solution and residual amorphous phase was stable rather than an amorphous single phase, thermal equilibrium crystalline phase and quasi-crystalline phase under 2.0MV electron irradiation at 298K, resulting in the formation of nano-composite structure by irradiation induced amorphization and crystallization.

We investigated the influence of annealing on the nanometer-scale medium-range order in Zr54Cu38Al8 bulk metallic glass using fluctuation electron microscopy. Fluctuation microscopy experiments probing structure at a length scale of 1 nm show that the as-cast Zr bulk metallic glass contains significant medium range order. That structure is unchanged by annealing at 87% of the glass transition temperature for 24 hours, although that anneal does significantly change the differential scanning calorimetry trace.

We performed nanoindentation creep experiments on the bulk metallic glass Zr54Cu38Al8 in an effort to measure the scale of the individual deformation events responsible for plastic deformation. From a nanoindentation creep experiment, we can determine V*, the activation volume, which we interpret as the volume of a shear transformation zone (STZ) multiplied by the shear strain undergone by the STZ during thermal activation. For the as-cast alloy hardness, H, is 5.33 ± 0.06 GPa, and V* is 87 ± 5 Å3. The alloy was then annealed near Tg for 24 hr and retested. No crystallization occurred during annealing as verified by XRD and TEM. Following annealing H increased to 7.36 ± 0.08 GPa and V* increased to 160 ± 10 Å3. We interpret the change in V* as arising from an increase in the number of atoms involved in the STZ.

An extremely promising microscale processing method for bulk metallic glasses called thermoplastic forming has emerged in recent years. However, most of the recent experimental thermoplastic forming studies have been conducted by trial-and-error. In this paper, we use the large-deformation constitutive theory of Henann and Anand [1] as a numerical simulation tool for the design of a micro-hot-embossing process. This numerical simulation capability is used to determine appropriate processing parameters in order to carry out a successful micron-scale hot-embossing operation on the metallic glass Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vitreloy-1). By carrying out a corresponding physical experiment, we demonstrate that micron-scale features in Vitreloy-1 may be accurately replicated under the processing conditions determined by use of the numerical simulation capability.

Metallic glass-forming liquids and glasses are ranked using thermophysical properties (glass transition, excess entropy, fragility indexes). The relationships between mechanical properties and some of the above quantities are discussed to get insight into the mechanism of shear band propagation during mechanical failure when, following up a shear offset event, a local temperature rise occurs. The mechanism is supported by evaluating the energy content of the shear band, as well as finite element modelling of temperature profiles around it.

The processing map for Zr-based bulk metallic glasses with crystalline in-situ precipitates (â phase) has been constructed from high temperature phase information, chemical composition analysis, and â phase crystallization kinetics. The phase evolution was detected in-situ by high energy synchrotron X-ray, and kinetic information on crystalline phase was measured from electrostatic levitation facility (ESL). This processing map offers a unique opportunity to control both volume and size of the dendritic â phase through composition and processing condition manipulation. The volume fraction of â phase can be customized from 6% to 93 %, and dendrite size is controllable between 1 and 50 µm at the current stage.

New Zr based metallic glass wires without bio-toxic elements of Ni, Al and Be were devel-oped for the further application as biomaterials by arc-melting type melt-extraction method. The continuous metallic glass wires with a good white luster and smooth surface were obtained in Zr-Ti-Al-Co, Zr-Al-Co-Cu, Zr-Al-Co and Zr-Ti-Co alloys. The Zr-based metallic glass wires show high tensile strength reaching 1000MPa. Furthermore, the wires exhibit good bending duc-tility and can be bent through 180 degrees without fracture. The Zr-based metallic glass wires achieve simultaneously high tensile strength, good bending ductility and high thermal stability.

A Zr65Al7.5Ni10Cu17.5-xPdx (x=0-17.5 at. %) alloy system is found to exhibit a unique dependence of glass-forming ability (GFA) on casting atmosphere during mold-casting process. High-Pd containing alloys (x=7.5-17.5) showed a remarkable increase of critical size (dc) for glass formation, in contrast with the low-Pd containing alloys (x=0-5) in which no significant change in dc was observed, as the pressure of Ar atmosphere varied from vacuum to ambient. The origin of the phenomenon has been successively unveiled by correlating the cooling characteristic during casting process and phase transformation behavior during continuous cooling of the alloy system. The consequence in the structure and property control is investigated and discussed in detail.

Structural relaxation around free volume in Zr50Cu40Al10 bulk metallic glass (BMG) during isothermal annealing at 473, 573 and 673 K which are below glass transition temperature Tg =675 K have been investigated by positron annihilation lifetime (PAL) and coincidence Doppler broadening (CDB) measurements. The trends of change in positron lifetime, which correspond to the size of free volume at each annealing temperature, have a good correlation with their density change. These annealing processes obey a stretched exponential relaxation function (KWW: Kohlrausch-Williams-Watts law). Fitting parameters of KWW function, with relaxation time t0 and β, in each temperature were determined. These relaxation parameters depend on the annealing temperature, suggesting the distribution of activation energy for structural relaxation. Moreover, the profile of electron momentum distribution around free volume derived by CDB spectrum during annealing showed no appreciable change at each temperature. These facts suggest that long range chemical ordering, particularly around the free volume, dose not take place essentially.

The goal of recent shear-transformation-zone (STZ) theories has been to construct a phenomenological description of amorphous plasticity that is based on physical principles and molecular models, and yet is simple enough to be useful in predicting the performance of real materials. In reporting progress toward this goal, I focus on the dynamic role played by the effective disorder temperature (a generalization of the free-volume) in controlling relaxation rates and predicting shear-banding instabilities.

Correlations between three characteristic temperatures: glass transition, Tg, Kauzmann, Tk, and Vogel-Fulcher-Tammann, To, were identified from the analysis of more than 60 metallic and non-metallic glass-forming materials. It was found that Tg ≥ Tk ≥ To and Tk is the geometric mean of Tg and To. The relation Tk ≥ To indicates that the excess total entropy of a super-cooled liquid ΔS approaches zero at a higher temperature than the configurational entropy ΔSconf, and such behavior was explained by the stronger temperature dependence of the excess vibrational entropy of the liquid, ΔSvib, than that of the corresponding glass, . A relationship between the fragility index m, reduced excess heat capacity ΔCp(Tg)/Sm, and reduced glass transition temperature, Trg, was identified using the found correlation between the characteristic temperatures.

We report a strong geometry-dependence of compressive plasticity in a Zr-based bulk metallic glass (BMG). With a standard orthogonal geometry, the Zr-based BMG typically fractured at a plastic strain less than 2%. However, by modifying the sample geometry while maintaining the sample aspect ratio, a large apparent compressive plastic strain over 10% was achieved consistently. These results present a new method on arresting the catastrophic failure of the glassy alloys and offer ways for BMGs in engineering applications.

Pd-Ni-P films were systematically plated using a mixture of Pd and Ni-P plating solutions. The films were plated by electroless alloy plating using three Pd/Ni-P mixture ratios (1/1, 3/1, and 1/3) at plating temperatures adjusted within a range from 303 to 333K. An increase in the Ni-P mixture ratio or in the plating temperature led to an increase in the Ni content of the plated film and a decrease in the Pd content. The P content of the plated film remained almost constant. These results indicate that the composition of the fabricated film can be effectively controlled by adjusting the plating temperature and mixture ratio. The plated film had a flat surface morphology without defects such as pinholes or nodules. TEM observation of the film revealed an amorphous structure. DSC analysis during heating revealed an endothermic peak and exothermic peak corresponding to the glass transition and crystallization, respectively. On the basis of these results, we concluded that the plated Pd-Ni-P film was metallic glass. The plated Pd-Ni-P film was also confirmed to have catalytic activity, as the Ni-P alloy was plated directly onto the film without catalyzation by electroless plating. The high flatness and uniformity of the surface of the Ni-P film plated onto the Pd-Ni-P film suggests that the Ni-P film grew via a one-dimensional growth mechanism.

The fracture toughness of Zr-based bulk metallic glasses of various compositions was studied in the as-cast and annealed condition. Properties were characterized using x-ray and differential scanning calorimetry (DSC) and fracture surfaces were examined using electron microscopy (SEM). Quaternary Zr-Ti-Cu-Be alloys consistently had linear elastic fracture toughness values greater than 80 MPa·m1/2, while Vitreloy 1, a Zr-Ti-Cu-Ni-Be alloy, had an average fracture toughness of 48.5 MPa·m1/2 with a large amount of scatter. The addition of iron to Vitreloy 1 reduced the fracture toughness to 25 MPa·m1/2. Fracture surfaces were carefully analyzed using electron microscopy. Some samples had highly jagged patterns at the beginning stage of crack propagation, and the roughness of this jagged pattern correlated well with the measured fracture toughness values. These jagged patterns, the main source of energy dissipation in the sample, were attributed to the formation of shear bands inside the sample. The Zr-Ti-Cu-Be alloy, having KQ=85 MPa·m1/2 as cast, was annealed at various time/temperature combinations. When the alloy was annealed 50°C below Tg, the fracture toughness dropped to 6 MPa·m1/2, while DSC and X-ray showed the alloy to still be amorphous. The roughness of the fracture surfaces on relaxed samples also compared well with the relative fracture toughness.

The compression behavior of Zr15Al5Ni57Y23 bulk metallic glass is investigated at room temperature using in-situ high pressure energy dispersive X-ray diffraction with a synchrotron radiation source. The structural information of the atomic configuration about Zr15Al5Ni57Y23 bulk amorphous alloy such as coordination number (CN), neighbor atomic distance is gained by Fourier transformation under different pressure. The investigation shows that the structure of Zr15Al5Ni57Y23 bulk metallic glass is stable under the pressure ranging from zero to 31.7 GPa, but the degree of short-range order changes by the pressure altering the second and the third nearest neighbor local atomic configuration of the amorphous alloy.

Molecular Dynamics simulations of molten oxides, such as fluid silicon dioxide and germanium dioxide, based on simple classical pair potentials, are compared with corresponding Car-Parrinello “ab initio” Molecular Dynamics (CPMD) work and with experiment. It is shown that CPMD provides a significantly better account for properties on short length scales, but classical MD is still indispensable to deal with larger scales of length and time. The behavior of the mean square displacement of the particles as well as the incoherent intermediate scattering function is compatible with a mode coupling description, at least at very high temperatures, while the diffusion constants show a crossover to Arrhenius behavior near the mode coupling critical temperature of these systems. Finally, the results for the network forming liquids are compared to those from simulations of binary metallic alloys such as Al80Ni20, which form a structure similar to densely packed hard spheres.

Volume and enthalpy relaxation processes in a sub-Tg region were investigated by density and enthalpy experiments for bulk Pd-P based and Zr-based metallic glasses. Most of glasses except for a Pd40Ni40P20 glass exhibited a single relaxation process for both volume and enthalpy relaxations and the relaxation process was well described by a stretched exponential relaxation function, Φ(t)=exp{-(t/τ)β}, with a Kohlrausch index β less than 1. The as-quenched sample was pre-annealed in a supercooled liquid region to homogenize the density fluctuation quenched in an as-quenched state. Then the retardation of onset time of relaxation appeared in case of volume relaxation. The proportionality between enthalpy change ΔH and volume change Δv during relaxation was good for Pd42.5Cu30Ni7.5P20 glass within experimental error.