Increased functions of osteoblasts (bone-forming cells) have been demonstrated on nanophase compared to conventional ceramics (specifically, alumina, titania, and hydroxyapatite), polymers (such as poly-lactic-glycolic acid and polyurethane), carbon nanofibers, and composites thereof. Nanophase materials are materials that simulate dimensions of constituent components of bone since they possess particle or grain sizes less than 100 nm. However, to date, interactions of osteoblasts on nanophase compared to conventional metals remain to be elucidated. For this reason, the objective of the present in vitro study was to design, fabricate, and evaluate osteoblast adhesion on nanophase metals (specifically, Ti and Ti6Al4V). Results of this study provided the first evidence of increased osteoblast adhesion on nanophase compared to conventional Ti-based metals. Moreover, directed osteoblast adhesion was observed preferentially at metal particle boundaries. It is speculated that since more particle boundaries were created through the use of nanophase compared to conventional metals, increased osteoblast adhesion resulted. Because adhesion is a necessary prerequisite for subsequent functions of osteoblasts (such as deposition of calcium-containing mineral), the present study suggests that Ti-based nanophase metals should be further considered for orthopedic implant applications.

Using high-precision X-ray dilatometry, we have succeeded in directly measuring excess quenched-in free-volume Vf in metallic glasses. The method was applied to the very easy glass forming Zr57Nb5Cu15.4Ni12.6Al10 (Vit 106). The annealing out of the order of 0.5% free volume was observed during heat treatment of rapidly solidified glassy ribbons. Excess free volume was also generated by heavy deformation and observed to anneal out during heat treatment. Once the excess free volume anneals out, the glass transition Tg appears clearly as a break in the x-ray dilatation curves as the glass goes over to the supercooled liquid region prior to crystallization at Tx.

The glassy structure and the primary precipitation phase from supercooled liquid were examined in metal-metal type Zr-, Hf- and Cu-based alloy systems by various advanced analytical techniques. The icosahedral phase precipitates as the primary phase from supercooled liquid for all the metal-metal type glassy alloys examined in the present study. The icosahedral phase has a rhombic triacontahedra type for the Zr-Al-Ni-Cu-NM (NM=Ag, Pd, Au, Pt), Zr-Cu-NM, Hf-Al-Ni-Cu-NM, Cu-Zr-Ti-Pd and Cu-Hf-Ti alloys. In addition, the short-range atomic configurations in their glassy alloys have the features of highly dense packed atomic configuration, new local atomic configurations and long-range homogeneity with attractive interaction. It is therefore concluded that the high glass-forming ability of the metal-metal type alloys is due to the self-formation of the unique glassy structure with the above-described three features which are consistent with the formation of short-range icosahedral atomic configuration.

With atomistic force fields derived from ab-initio energies and atomic forces, we cooled Fe80B20 from the liquid to the glass state. The pair-distribution functions and the diffusion coefficients were used to characterize the structural changes that Fe80B20 underwent during the simulation. In the FeFe and FeB pair-distribution functions, when the temperature is lowered the first neighbor-peak becomes narrower and the second-neighbor peak splits at around 1000K. In the BB pair-distribution we observed that the first peak undergoes a significant change at the glass transition temperature, and that the first BB peak remains present at low temperatures. That the first BB peak exists at low temperature seems to contradict the prevailing view of the structure of transition metal-metalloid glasses.

The bulk amorphous Fe-based alloy with the nominal composition Fe65.5Cr4Mo4Ga4P12C5B5.5 was obtained by copper mold casting in different shapes: cylindrical rods with diameters up to 2.5 mm and discs with 10 mm diameter and 1 mm thickness. This alloy exhibits good soft magnetic properties. Using electrochemical investigations we found that the corrosion resistance of this alloy is better than that of usual FeSi steel used for magnetic applications. Beside magnetic properties and corrosion resistance, this alloy exhibits also good mechanical properties. These were investigated by compression tests, nanoindentation and by an ultrasonic technique. The Young's modulus E was found to be around 160 GPa, the yield strength σy is around 2.3 GPa and the fracture strength σf is around 3.23 GPa, together with an elastic strain εe= 1.5% and a fracture strain εf= 2.3%. The hardness was found to be around 10 GPa.

We present evidence of the nucleation and growth of a metallic glass phase from the melt, as if by a first-order transition. Microstructures of a number of rapidly solidified Al-Fe-Si alloys demonstrate that this glassy phase, which we term q-glass, is not a kinetically frozen liquid. It is the first phase to form from the melt as isolated nuclei that grow and deplete the melt of iron and silicon. From the nucleation behavior and the compositional partitioning, we infer an interface between the q-glass and the melt, and that, in a narrow composition range, the q-glass has a lower energy and entropy (is more ordered) than a conventional glass.

The results of a transmission electron microscopy study on the crystal structures and morphologies exhibited by each of the phases in a set of four Al-rich Al-Y-Ni alloys which contain 1.7–4.5 at. % Y and 3.5–10.1 at. % Ni are presented. It is shown that each alloy contains fcc-Al, a binary Al3Ni or Al3Y phase (depending on alloy composition), and a ternary phase. The same ternary phase was found in each alloy and this was found to correspond to a new phase Al19Ni5Y3 (Cmcm, a=0.4025 nm, b=0.799 nm and c= 2.689 nm, Al19Ni5Gd3 structure type). In many cases, the ternary particles also contain embedded slabs of the equilibrium Al23Ni6Y4 phase. This phase mixture did not decompose even after extended annealing.

Recently refractory alloy glasses of varying Ni, Nb and Sn concentrations were prepared and studied via several characterization methods, including x-ray diffraction via standard lab and synchrotron radiation sources, SEM, and other complementary techniques. A comparison between x-ray diffraction results obtained from synchrotron sources vs. standard lab sources shows the necessity of a low-divergence source in order to distinguish nanoscale crystallites present within an amorphous matrix. The divergence of both sources was determined by comparing the diffraction patterns of a LaB6 standard and noting the deviation from ideal or theoretical Bragg peaks. The crystallites in these glasses comprised between 0 and 7.5 percent by volume, depending upon the specific composition. The results presented here also show a very good sample-to-sample consistency for any given alloy composition. While x-ray diffraction results give information about the average structure, SEM was also performed to understand aspects of individual crystallite size and distribution. By studying results of varying alloy concentrations, it is seen that a very small composition range exists for near-perfect glass formers (as defined by a near zero percentage crystallinity). Radial distribution analysis was also performed for each composition and compared to hard sphere models for each alloy composition. This analysis indicated the presence of intermediate range order beyond the first nearest neighbors as indicated by the divergence of the experimental reduced radial distribution functions from that predicted by the accompanying hard sphere models.

We report on the microstructure, the thermal stability and the mechanical properties of slowly cooled Zr-Nb-Cu-Ni-Al alloys with ductile bcc phase precipitates embedded in a glassy or nanocrystalline matrix. The samples were prepared in form of rods by injection casting into a copper mold. The phase formation and the microstructure of the composite material were investigated by X-ray diffraction, EDX analysis and scanning and transmission electron microscopy. The thermal stability was examined by differential scanning calorimetry and the mechanical behavior was investigated by compression tests under quasistatic loading at room temperature. The formation of bcc phase dendrites and a glassy or nanocrystalline matrix is strongly governed by the alloy composition and the actual cooling rate during solidification. Besides, changes in composition and cooling rate lead to different volume fraction and size of the bcc phase precipitates and, hence, to different values of yield strength, elastic and plastic strain. The samples with nanocrystalline matrix show a homogeneous distribution of the bcc phase precipitates over the whole cross-section and exhibit higher yield strength and plastic strain than the samples containing an amorphous matrix. Illustrated by the presented results we show the possibility of obtaining tailored mechanical properties by control of composition and solidification conditions.

Molding of fine surface features into a bulk metallic glass (BMG) from the molten state was investigated. It was studied down to which a feature size in a mold could be reproduced in the BMG. A new casting apparatus was designed and built to carry out the experiments. The BMG used was Vitreloy 1™, Zr41.24Ti13.75Cu12.5Ni10Be22.5, and it was observed to replicate mold features down to several nanometers. This has been verified with SEM photographs of both the mold surfaces and the BMG parts. Processing variables, including the injection temperature of the molten BMG and the atmosphere, in which it is molded, appear to have a great effect on the ability to reproduce the fine features on the mold surface.

Metallic glasses exhibit generally high hardness and elastic modulus values at the expense of very limited plasticity. The incorporation of crystalline particles within an amorphous metallic matrix has been widely reported to improve the performance of these materials by reducing crack propagation. The present work analyzes the influence of nanometer-size ZrC particles on the nano-mechanical behavior of mechanically alloyed Zr55Cu30Al10Ni5 glassy matrix composites. The volume fraction of ZrC particles ranged from zero up to 20 vol. %, showing a critical change in the mechanical behavior between 10 and 20 vol. %, particularly in the elastic response.

Heat evolution of stress-induced structural disorder, ΔHs(ε), of a Zr55Al10Ni5Cu30 bulk metallic glass (BMG) during constant ram-velocity deformation at the glass transition region (Tg= 680 K) was deduced from in-situ measurements of temperature change of the deforming sample. At the transition from the linear to nonlinear viscoelasticity, the behavior of viscosity change with strain, η(ε), is qualitatively consistent with the enthalpy evolution of the structural disordering, ΔHs(ε), but not with the temperature change, ΔT(ε). It is concluded that the initial softening deformation is due to the stress-induced structural disordering. The change in the nonlinearity, -log ñ ≡ −logη/ηN, is found to be proportional to the ΔHs and the slope of ΔHs(–logñ) can be estimated to ∼ 400 J/mol, where ηN is the Newtonian viscosity. On the other hand, the temperature raise, ΔT(ε), is pronouncedly delayed as compared with the η(ε) and ΔHs (ε) at the transition, but is determined by the product of stress and plastic strain-rate, σ·εp, and is nearly proportional to it at the steady-state. The slope of ΔT(σ·εp) can be estimated to 5.2×10-2 K mol/W.

In bulk metallic glasses cooled at nearly the critical cooling rate for glass formation, nucleation is observed to be spatially localized; nanocrystals are clustered together in spherical regions. This implies that a positive feedback mechanism locally increases the nucleation rate in the vicinity of other nucleation events. Linear stability analysis and computer simulation of differential equations describing crystal nucleation and growth are used to theoretically examine the plausibility of different potential feedback mechanisms. It is shown that interactions between different crystallizing phases can lead to counter-intuitive composition dependence of the crystallization kinetics in the case of non-polymorphic crystallization.

Fatigue crack propagation mechanisms of bulk metallic glasses (BMGs) are not well understood, limiting their use in safety-critical structural applications particularly where complex fatigue loading may occur. Accordingly, the present study examines the effects of variable amplitude fatigue loading associated with block loading and tensile overloads on fatigue crack-growth rates in a Zr-based BMG. Crack growth studies were conducted on compact tension specimens using computer control of the applied stress intensity range, ΔK. Fatigue crack closure loads, which represent the initial contact of mating crack surfaces during the unloading cycle, were continuously monitored during testing. Abrupt drops in ΔK were found to significantly decrease fatigue crack-growth rates far below equilibrium values, arresting growth completely at a ΔK twice the nominal fatigue threshold ΔKTH. Conversely, an abrupt increase in ΔK was found to accelerate fatigue crack-growth rates. The effects of roughness-induced crack closure were assessed and found to be consistent with the suppression or acceleration of growth rates. However, in order to fully explain the observed transient growth rate response, other mechanisms that may be related to the fatigue mechanism itself were also considered. Specifically, the nature of the fatigue crack tip damage zone was also investigated. As BMGs lack distributed plasticity at low temperatures, the plastic zone differs greatly from that seen in ductile crystalline materials, and its role in fatigue crack propagation mechanisms is examined.

The free volume changes associated with deformation of metallic glasses play an important role in strain localization in shear bands. However the details of these structural changes during inhomogeneous deformation are unclear. In this study, the free volume changes in Cu60Zr30Ti10 and Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 bulk metallic glasses were examined and quantified using differential scanning calorimetry following rolling and low temperature annealing. It was found that the height of the endothermic peak associated with the glass transition decreased following deformation whereas annealing resulted in an increase in the peak height. Additionally, the exothermic event associated with structural relaxation prior to the glass transition occurred at a lower temperature after rolling in the Zr-based system. Surprisingly, a similar shift in the onset temperature was not observed in the Cu-based system, suggesting a different structural relaxation mechanism. The Zr-based system was successfully modeled and the results indicated that the free volume increased ∼4% with inhomogeneous deformation and decreased ∼14% with annealing, consistent with expectations. In an effort to further characterize strain localization in shear bands, the development of a crack tip damage zone in a Zr-based bulk metallic glass composite was studied using scanning electron and atomic force microscopy. The first shear band developed at an angle of ∼60° from the crack propagation direction. This is discussed in light of the Mohr-Coulomb yield criterion for metallic glasses. The reinforcement phase arrested the growth of individual shear bands, while accumulated damage resulted in the shear bands cutting through the crystalline phase, ultimately resulting in crack branching and failure.

Isothermal relaxation studies of the Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 bulk metallic glass forming alloy were performed using Differential Scanning Calorimetry in the glass transition and the supercooled liquid region. A new experimental method was developed to study the isothermal enthalpy relaxation kinetics. The results reveal that the enthalpy relaxes in an Arrhenius fashion. The activation energy obtained from the Arrhenius fit is comparable to the activation energy required for the diffusion of the medium size atoms. This suggests that the solid-state diffusion governs the enthalpy relaxation process. The stretching exponents for the relaxation are close to unity, which indicates that the alloy is a rather strong glass former.

High-cycle fatigue (HCF) studies were performed on zirconium (Zr)-based bulk metallic glasses (BMGs): Zr41.2Ti13.8Ni10Cu12.5Be22.5, in atomic percent. The HCF experiments were conducted using an electrohydraulic machine at a frequency of 10 Hz with a R ratio of 0.1 and under tension-tension loading, where R = σmin./σmax., where σmin. and σmax. are the applied minimum and maximum stresses, respectively. The test environment was air. A high-speed and high-sensitivity thermographic-infrared (IR) imaging system has been used for nondestructive evaluation of temperature evolution during fatigue testing of BMGs. Limited temperature evolution was observed during fatigue. However, no sparking phenomenon was observed at the final moment of fracture of this BMG. At high stress levels (σmax. > 864 MPa), the fatigue lives of Batch 59 are longer than those of Batch 94 due to the presence of oxides in Batch 94. Moreover, the fatigue-endurance limit of Batch 59 (703 MPa) is somewhat greater than that of Bath 94 (615 MPa) in air. The fatigue-endurance limit of Ti-6–4 is greater than this BMG, but Al 7075 has the lowest fatigue life. The vein pattern with a melted appearance were observed in the apparent melting region. The fracture morphology indicates that fatigue cracks initiate from some defects.

We use a fluid mechanics model to analyze glass fluid flow during the welding of bulk metallic glasses with reactive multilayer foils acting as local heat sources. The resulting welded joints were shear tested, and fracture surfaces were analyzed by optical microscopy. Fracture surfaces of failed metallic glass joints show distinct regions of metal-metal veins that indicate effective metallurgical bonding. We observe a monotonic increase in the failure strength of the joints with the fraction of the joint composed of such veins. For the strongest joint tested (shear strength of 420 MPa), nearly 60% of the fracture surface is comprised of metal-metal veins. We have developed a qualitative fluid mechanics explanation of the welding process, in which shear stresses (due to pressure applied during joining) push the reactive foil from the joint interface and create the metal-metal veins. The welding process is more effective at higher joining pressure and greater foil thickness, leading to increased joint strength.

Amorphisation studies by rapid solidification of Al-based alloys containing a transition metal (TM) and a rare earth element (RE) are reported. Results on primary formation of Al nanocrystals are given and discussed in relation to possible nucleation mechanisms considering the effect of various RE elements (RE = La, Ce, Nd and Sm) in Al87Ni7RE6 alloys. Ti or Zr, immiscible with RE's, are added to the ternary alloys with the aim of revealing possible phase separation in the melt. Calculations of ternary Al-Ni-Ce metastable phase equilibria are helpful in understanding the transformation sequence. Composition profiles ahead of nanocrystals are computed using the DICTRA software which correctly predicts the occurrence of composition gradients.

The surface fracture of mechanically tested samples are observed in TEM to check whether crystallisation is induced by deformation.

High energy synchrotron x-rays (124.63 keV) are used to investigate the initial stages of the devitrification for the Zr70Pd20Cu10 metallic glass prepared by melt-spinning (MS). Due to the excellent signal:noise, we are able to determine the initial nucleating phase by analyzing the differences in the total scattering function S (Q) as a function of time at a temperature ∼ 50 K below the crystallization temperature. The alloy undergoes a structural relaxation prior to nucleation and growth. Devitrification proceeds from nucleation of the icosahedral phase. The differential pair distribution function (dPDF) indicates that the as-quenched alloy may have icosahedral-like order which undergoes local rearrangement to true icosahedral order at an annealing temperature 50 K below the crystallization temperature. More importantly, time-resolved high-energy synchrotron is shown to have excellent sensitivity to the initial atomic rearrangements preceding nucleation in metallic glasses.