Onset temperature, Tm and offset temperature (liquidus) Tl of melting of a series of bulk glass forming alloys based on La, Mg, and Pd have been measured by studying systematically the melting behaviour of these alloys using DTA or DSC. Bulk metallic glass formation has been found to be most effective at or near their eutectic points and less effective for off-eutectic alloys. Reduced glass transition temperature Trg given by Tg/Tl is found to show a stronger correlation with critical cooling rate or critical section thickness for glass formation than Trg given by Tg/Tm.

We have explored the short-range order around all three constituent atoms in (Pd-Ni)80P20 bulk metallic glasses (BMGs), a system that is a prototype for a whole class of BMG formers containing 80% transition metal and 20% metalloid. We have examined the changes in the nearest neighbor environments around the transition metals in (Pd-Ni)80P20 glasses using extended X-ray absorption fine structure (EXAFS) in comparison to their binary counterparts. We have done similar studies around the coordination of P using extended energy loss fine structure (EXELFS). The environment around the all the atoms in Pd60Ni20P20 and Pd30Ni50P20are very similar to those of the binary phosphides at the ends of the composition range. However, the (Pd-Ni)80P20 glasses are not simply solid solutions of the phases. The nearest neighbor distances of the metals are reduced in the ternary alloys with respect to those of the binary phosphides. The best glass former in this series, Pd40Ni40P20 is nearly isostructural to Pd30Ni50P20 but shows shorter distances at the 2nd and 3rd coordination shells, which we believe is due to more efficient packing in this glass. The metal environments in Pd40Ni40P20, on the other hand, are better described by a weighted average of those of Pd30Ni50P20 and Pd60Ni20P20.

For the Ni-Zr and Ni-Ti systems, Molecular-dynamics (MD) simulations are conducted to compare the relative stability of the terminal solid solutions versus the corresponding amorphous states as a function of solute concentrations. It turns out that the terminal solid solutions transform into an amorphous state spontaneously when the solute concentrations are beyond the maximum allowable values, i.e. the critical solubilities, determined to be 14 at.% Zr in Ni and 25 at.% Ni in Zr for Ni-Zr system and 38 at.% Ti in Ni and 15 at.% Ni in Ti for the Ni-Ti system, respectively. The glass-forming ranges are therefore deduced to be within the respective critical solubilities, i.e. 14-75 at.% Zr and 38-85 at.% Ti for the Ni-Zr and Ni-Ti systems, respectively, which are compatible with those from experiments and/or from the generalized Lindemann criterion. Moreover, MD simulation also reveals that solid-state amorphization does take place and that the growth of the amorphous interlayer follows exactly a t½ law. Besides, a solubility criterion is proposed that the lower the maximum solid solubility the less stable is the lattice of the metal upon solid-state reaction and it can explain the fact that the growing speed of amorphous interlayer toward Ni (melting point = 1528 K) is greater than that directed to the Zr (2128 K) lattice, while it is smaller than that to Ti (1941 K) side.

Bulk Mg-Cu-Y-Al alloys, prepared by casting into a wedge-shaped copper mold, have been studied in the as-prepared, the supercooled liquid, and the crystalline states. In the as-prepared state x-ray diffraction of sub-millimeter sized regions were performed using a focused x-ray beam. The phase composition of the cross section as well as of the surface of the wedge-shaped specimen was investigated as a function of position. The cooling history of the alloy was experimentally determined and compared to results of a control-volume finite-difference modelling study. The experimentally determined and the calculated cooling rates were correlated with the observed amorphous/crystalline structure. The transition from an amorphous to a crystalline state was followed by x-ray diffraction studies as a function of time at specific temperatures in the region between the glass transition and the crystallization temperature. Based on these results a temperature-time-phase diagram was constructed. The dependence of external pressure on the crystallisation temperature was investigated by in situ high-temperature and high- pressure x-ray powder diffraction by using synchrotron radiation. The investigations form the basis for a selection of the optimum temperature in the supercooled liquid region for performing deformation/shaping of the Mg-based alloys.

A molten Pd82Si18 alloy, free of potent heterophase impurities and enclosed in a fused silica tube of conical shape, was quenched in water. Four regions classified according to their microstructures can be distinguished. They are: region I, amorphous; region II, a mixture of an amorphous nanostructure and a nanocrystal; region III, a mixture of two kinds of nanocrystals; region IV, spinodal networks; and region V, conventional eutectic structure. The detailed microstructures in each region are discussed.

Composites consisting of a bulk metallic glass (BMG) matrix and metallic fibers or particulates have been shown to exhibit superior mechanical properties as compared to monolithic BMGs. To understand the role of reinforcements in this improvement, it is necessary to investigate the state of internal stresses in these composites. These stresses arise from the thermal expansion mismatch between the reinforcement and the matrix, as well as the elastic and plastic incompatibilities between the two phases. Neutron diffraction and synchrotron X-ray diffraction were used to measure these mismatch-induced stresses in BMG-matrix composites with various reinforcements: continuous W fibers, W or Ta particles, and dendritic, in-situ formed precipitates. The results are compared to numerical and analytical predictions of internal stresses.

Tribological properties of bulk metallic glass Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 were studied experimentally using a pin/disk geometry without lubrication. Experimental observations were compared with 2D molecular dynamics simulations of amorphous material in sliding contact. The friction coefficient and the wear rate of bulk metallic glass (BMG) depend on normal load and test environment. The sliding of annealed BMG re-amorphizes devitrified material. A mechanically mixed layer is generated during sliding; this layer has enhanced oxygen content if the sliding is in air. The MD simulations show that atomic scale mixing occurs across the sliding interface. The growth kinetics of the mixing process scales with the square root of time. In the simulations, a low density region is generated near the sliding interface; it corresponds spatially to the softer layer detected in experiments. Subsurface displacement profiles produced by sliding and by simulation are very similar and are consistent with the flow patterns expected from a simple Navier-Stokes analysis when the stress state involves both compression and shear.

Cylindrical composite Zr55Al10Ni5Cu30 bulk glassy alloys containing up to 17.5 vol.% ZrC particles were prepared with using an in-situ reaction forming ZrC between graphite particles with diameters of ∼10 m and Zr metal in molten alloy during arc-melting followed by copper mold casting. Because the in-situ reaction suppresses an agglomeration and segregation among dispersoids in the glassy matrix, mechanical properties of the composite materials at room temperature, especially toughness and plastic elongation, were significantly improved from the Zr55Al10Ni5Cu30 single glassy phase. In order to demonstrate the influence of the dispersed ZrC particles on workability of the supercooled liquid of the alloy, viscous flow behaviors under constant strain-rates were investigated. Although the Newtonian viscosity becomes larger, the composite material has the same viscoelastic properties, i.e., “shear thinning”, and excellent workability as the single glassy phase in spite of the dispersed particles.

Using the intrinsic materials properties of bulk metallic glasses (BMG), namely electrical resistivities two orders of magnitude higher than good conductors and a Newtonian viscous-flow regime of deformability, a new electromechanical process has been developed for shaping, joining and engraving of BMGs. The wider the liquid supercooled region between the glass transition temperature Tg and the crystallisation temperature Tx of the bulk metallic glass, the easier the application of the new process. In this range, the undercooled liquid deforms in a quasi-Newtonian way, allowing thermomechanical shaping in the low viscosity range as for oxide glasses. The new electromechanical processing technology has been used for economical and rapid shaping at low applied stresses by eliminating the thermal mass of the furnace and the need to heat the deformation dies. The process parameters are adaptable for the full maintenance of the glassy state or when desired, for appropriate compositions, for nanocrystallisation during the joining or shaping operation.

Mechanical spectroscopy technique has been applied to investigation of structural relaxation and crystallization of Mg-Ni-Y amorphous alloys of different composition. The composition of the alloys was varied due to change of yttrium concentration from 0 to 7 at.%. The internal friction (IF) and Young's modulus have been measured by a vibrating reed method at frequency of ∼200 Hz at heating and cooling runs in the temperature range from 300K to 650K. Crystallization kinetic studies of the alloys by DSC and XRD showed that the transition from amorphous to crystalline state in the Mg-Ni-Y alloys has gone through several stages with origination of intermediate phase. IF spectra and Young's modulus of the alloys have been analyzed and the effect of yttrium content on the stability of intermediate phase was investigated.

Titanium and zirconium based metallic glasses and crystalline intermetallic compounds with improved mechanical properties are presently a field of intense application-oriented research. The formation and stability of nanocrystalline phases in Ag-substituted Ti-Zr-Ni alloys was followed using in-situ high-temperature synchrotron radiation diffraction experiments. The substitution of Ti with Ag enhances the formation of amorphous or nanostructured phases during rapid solidification. High-resolution powder diffraction and electron microscopy investigations indicate that the as-quenched alloys are either amorphous or in a mixed nanostructured state. Upon heating, the alloy structure transforms to a fine mixture of icosahedral and crystalline phases depending on the alloy composition and thermal processing parameters. Differential scanning calorimetry studies were performed in order to identify the nature and sequence of the observed structural phase transitions. The experimental results are discussed with respect to the non- equilibrium synthesis and processing of bulk amorphous and bulk nanocrystalline materials in Ti/Zr-based alloys.

We have prepared bulk metallic glasses of composition (HfxZr1-x)52.5Cu17.9Ni14.6Al10Ti5 (with x=0-1) by an arc melting/suction casting method. The density of these alloys increases by nearly 67% with increasing Hf content, which is advantageous for their potential use as kinetic energy armor-piercing projectile materials. The glass transition temperature and the melting temperature increase linearly with increasing Hf content. The reduced glass transition temperature (Tg/Tm) decreases from 0.64 (x=0) to 0.62 (x=1), indicating reduced glass-forming ability for the Hf- based alloy. The fracture strength in uniaxial compression at quasi-static strain rates also increases with increasing Hf content, reaching ∼ 2.2 GPa for Hf52.5Cu17.9Ni14.6Al10Ti5.

Several alloys of the Zr65×−yTixAlyCu22Ni13 system were found to be bulk metallic glasses. They have been investigated by DSC and in-situ neutron diffraction. DSC and neutron studies were performed at the same heating rates in order to correlate the evolution of the characteristic temperatures to the crystallization of phases. The first phase appearing at crystallization is dependant on the titanium content, being Zr2Ni for Ti ≈ 5% and a quasi- crystalline phase for Ti ≈ 2.5%. These phases are metastable and transform to Zr2Cu and other phases.

Bulk metallic glasses have extremely high strength and high ductility and are quite useful as the structural material. Many of bulk metallic glasses are based on Zr, Ti and Pd; these elements have a high affinity with hydrogen and hence the bulk metallic glasses can contain a large amount of hydrogen atoms. It is known that hydrogenized amorphous metals, as well as hydrogenized metallic crystals, exhibit Snoek-type relaxation, and hence metallic glasses containing a high density of hydrogen can have a high internal friction.

In the present experiments, internal friction measurements have been performed for bulk metallic glasses doped with a variety of hydrogen concentrations. It is shown that the peak value of the internal friction reaches the order of 10-2 in Zr-based bulk metallic glasses which have the fracture strength as high as 1.5 GPa. Thus, hydrogen-doped bulk metallic glasses can be used as the high-strength, high-damping material.

It is found that a nano icosahedral phase with diameters below 50 nm is formed as a primary phase in the Zr70Ni10M20, Zr70TM10Pd20, Zr70Au10Pd20 and Zr75Pt10Pd15 ternary and Zr70Pd30 binary glassy alloys. The nanoscale icosahedral phase in the diameter range below 10 nm was also found to be formed directly in the melt-spun Zr80Pt20 binary alloy. These icosahedral phases transform to the crystalline phase(s) at the higher annealing temperature. The nucleation kinetics for the precipitation of the icosahedral phase from supercooled liquid were examined in the Zr70Pd30 and Zr70Ni10Pd20 glassy alloys. It was clarified that the transformation of both alloys proceeds in the diffusion-controlled growth mode with increasing nucleation rate. The formation of the nanometer-scale icosahedral phase is due to the transformation mode. The activation energy of nucleation is evaluated to be 267 kJmol−1 for the binary alloy and 311 kJmol−1 for the ternary alloy. The difference between the two alloy systems seems to originate from the difference in the number of atoms for rearrgements in the nucleation mode. The short-range ordering is observed in the as-quenched Zr70Pd30 glassy alloy, which is indicative of the icosahedral structure. The formation of the nano-scale icosahedral phase in the Zr-based binary and ternary alloys is due to the existence of an icosahedral short-range order in the glassy or liquid state. It is suggested that the icosahedral short-range order is stabilized by the restraint of the long-range atomic rearrangements that lead to the transition to a periodic structure by the strong chemical affinities of Pd or Pt with Zr.

The thermodynamic, transport and structural properties of a binary metallic glass former in solid, liquid, and glass phases were studied using molecular dynamics simulation. We used a model binary alloy system with a sufficient atomic size mismatch and observed a glass transition in a quenching process. The diffusivity and viscosity were calculated in the liquid state and the super-cooled liquid state. The smaller atom showed higher diffusivity and more configurational randomness compared to the larger atom. The viscosity increased abruptly around the glass transition temperature. The solvent/solute concentration effect on the glass transition was examined in terms of a packing fraction. We find that the glass forming ability increases with the packing fraction in the liquid state because the densely-packed material requires more time to rearrange and crystallize.

We have examined the structure of plastic deformation zones ahead of the tips of microcracks in Zr-based bulk metallic glass Zr57Ti5Cu20Ni8Al10. We have used an axially aligned dark field transmission electron microscopy technique, with the objective aperture placed to form images using electrons from several different areas of the diffraction patterns. We also compared Fourier transforms of the high resolution transmission electron microscopy images of deformed and undeformed regions to extract additional structural information. The plastic zones produce enhanced low-angle scattering of electrons and an apparent broadening of the amorphous halo, suggesting increased disorder and the presence of voids in the deformed zones. These results are consistent with an increased degree of atomic-scale disorder and enhanced free volume in highly deformed regions, which may provide a partial explanation of the manner in which plastic deformation occurs in metallic glasses.

Advanced diagnostic instruments and analyses applied to failure surfaces and cross sections of bulk metallic glasses (BMGs) can provide insight into the deformation and failure of these materials and assist in prototyping new materials with improved failure resistance. Confocal- optics scanning laser microscopic analysis of conjugate fracture surface topographs suggests that the formation and stretching of ligaments are likely keys to the high impact toughness of Vitreloy.

Self-diffusion coefficients of Ni in Zr55Al10Ni10Cu25and of Ni and Pd inPd40Cu30Ni10P20 bulk metallic glass below and above the glass transition temperature Tg have been measured with an ion-beam sputter-sectioning technique using the radioactive isotope 63Ni and 103Pd. The diffusion coefficients in the supercooled liquid region are much higher than those extrapolated from low temperature data in the amorphous region. The temperature dependence of the diffusion coefficients exhibits non-Arrhenius behaviour in the supercooled liquid phase. Such a deviation from the Arrhenius plots is interpreted by a cooperation of moving tracer atom with the surrounding atoms. The difference of the diffusion behaviour in between Zr-Al-Ni-Cu and Pd-Cu-Ni-P glasses is attributed to the different structural stability of both glasses.

Using a non-contact electromagnetic-acoustic transformation (EMAT) technique, we have measured the temperature dependence of the infinite frequency shear modulus of Vit 1 at constant heating rate in the glassy and supercooled liquid states. Values of the shear softening fragility parameter -dln(G/Gg/d(T/Tg) are compared with those obtainable from specific heat and viscosity measurements, using the interstitialcy theory of condensed matter states. There is overall agreement found between these independently measured values.