The effect of alternative preparation methods (copper mold casting, melt spinning, and mechanical attrition) on amorphization and properties of Nd57Fe20Co5Al10B8 and Nd40Fe40Co5Al8B7 alloys has been investigated. For all differently prepared samples an amorphous phase is formed upon solidification or solid sate reaction. However, the samples prepared by different processing routes exhibit different transformation behavior in thermal analysis. The cast Nd57Fe20Co5Al10B8 rod exhibits crystallization at 790 K followed by melting at 810 K. Neither appreciable endothermic reaction due to a glass transition nor a supercooled liquid region have been observed. Mechanically alloyed powders and ball-milled prealloys reveal two exothermic DSC peaks in the range of 650-850 K. The J-H hysteresis loops of samples synthesized by different routes show that the unique atomic order responsible for hard magnetic properties can only be accessed at moderate cooling rate of the melt as realized in copper mold casting. Rapidly quenched ribbons, mechanically alloyed powders and ball-milled ingots do not show hard magnetic properties at room temperature. These results indicate that amorphous samples with different local atomic order can be prepared by different processing routes.

We have introduced the theory of three-dimensional supercooled metallic liquids and glasses, which is based on the gauge invariant agrangian with spontaneous breaking, and discussed the viscosity of the three-dimensional supercooled metallic liquids. n the basis of the present theoretical formula, a qualitative picture of low energy excitations (the boson peak) is proposed.

The crystallization of bulk Zr48Nb8Cu14Ni12Be18metallic glass has been investigated by differential scanning calorimetry (DSC) and X-ray powder diffraction. The activation energies of glass transition and crystallization for the glass obtained using Kissinger analysis from the shift of the peak temperature in the DSC curve are 470 and 235 kJ/mol, respectively. The effect of applied pressure on crystallization is studied by in situ high-pressure and high-temperature X-ray powder diffraction using synchrotron radiation. It is found that the crystallization temperature increases with pressure having a slope of 9.5 K/GPa in the range of 0-4.4 GPa.

Modulated temperature calorimetry measurements on the bulk glass forming Pd40Ni40P20 alloy are reported in the frequency range between 1/30 s−1 and 1/1000 s−1. These measurements represent the first experimental assessment of the slow relaxation modes of a metallic liquid over a substantial frequency interval. The results reveal the typical behavior known for dissipative systems. The frequency-dependence of the dynamic specific heat is compared to results of dynamic rheology measurements that have been performed on the same material at similar modulation frequencies to compare the dynamic response of the respective modes.

Isotropic nanocrystalline Sm(Co,Zr)7 permanent magnet powders of the TbCu7 type structure and with high coercivity and enhanced remanent magnetization has been synthesized by mechanically milling Sm12.5Co87.5-xZrx alloys (x = 0, 1, 2, 3) alloys and subsequently appropriate annealing. The mechanical-milling process of the alloys and the formation of nanostructured Sm(Co,Zr)7 magnet powders have been investigated with respect to hard magnetic properties. Hard magnetic properties are found to be strongly dependent upon the processing condition (like milling time, annealing temperature, etc.). Optimal coercivity Hci of value above 21 kOe has been obtained in Sm12.5Co85.5Zr2 magnet powders subjected to milling for 5 hr and annealing at 600°C for 20min. Optimal remanent magnetization Mr of 73.4 emu/g, remanence ratio Mr/Ms of 0.71, and maximum energy products (BH)max of over 13 MGOe have been realized in Sm12.5Co87.5-xZrx (x = 1, 2) magnet powders with grain size of 15-20 nm. The hard magnetic properties are ascribed to the nanosized Sm(Co,Zr)7 phase of the TbCu7 type structure with grain size of 10-20 nm. The enhancement of remanent magnetization may be contributed from the enhanced exchange-coupling interaction between nanosized grains.

Three bulk metallic glasses, with different resistance against crystallisation, were investigated using DSC experiments, X-ray diffraction, transmission electron microscopy and mechanical spectroscopy. Like in other non-crystalline materials, the elastic modulus exhibits a large decrease above the glass transition temperature. In materials with a large supercooled region (Pd-Ni-Cu-P for instance), this decrease can reach three decades, leading to an attractive glass forming ability. In contrast, in bulk metallic glasses in which onset of crystallisation occurs very rapidly above Tg, this decrease is on less than one decade. A correlation is made with the microstructure evolution revealed by X-Ray diffraction and transmission electron microscopy.

A glassy structure was formed in the Fe40Co40P14B6 alloy by melt-spinning technique. The as-quenched 2-8 mm wide and 15-30 [.proportional]m thick ribbons exhibit good soft magnetic properties: the saturation magnetization of 1.45 T, the coercive force of 4 A/m and maximum differential permeability at 60 Hz of about 90000. The FeCo-based glass crystallizes via eutectic reaction into a mixture of an austenite and a b.c. tetragonal Fe3P-like phase similar to that of the well-known Fe40Ni40P14B6metallic glass, but at temperatures about 60 K higher than the latter. The evaluation of the thermodynamic and kinetic parameters of crystallization process brought us to the conclusion that the improved thermal stability of the Fe40Co40P14B6 glass is caused by the enhanced interfacial nucleus-glass energy.

Zr-Cu-Ni-Al exhibits one of the best glass forming alloys known. In a narrow concentration range, however, annealing leads to the formation of a metastable icosahedral phase. The aim of this paper is to investigate in detail the influence of alloying with Hf or Si, Sn, Y, Cr and Mo on the quasicrystal formation in Zr69.5Cu12Ni11Al7.5 glasses.

Whereas Y addition leads to loss in thermal stability and pronounced formation of quasicrystals, the addition of Si, Sn or Mo does not deteriorate thermal stability. Sn and Si were observed even to improve thermal stability significantly, but also to change phase selection during the early stages of crystallization. Si addition results in the formation of the tetragonal Zr2Ni phase and Mo as well as Cr to the formation of the fcc, so-called big-cube phase.

Nucleation rates for the quasicrystal formation were measured by means of crystallization statistics. By modeling the obtained nucleation rates in the framework of diffusion controlled classical nucleation the interface energies (between quasicrystals and amorphous matrix) as well as metastable melting temperatures for the quasicrystalline phase could be derived. In all cases nucleation could be described best with a homogeneous model with transient rates.

In order to understand the formation of the icosahedral structure also data on the influence of oxygen and hydrogen contamination as well as recent results of other authors on the influence of noble metals such as Ag, Pd, Au and Pt will be discussed in detail. There is some evidence that the quasicrystals are a hybrid of two structural elements, i.e. the tetragonal Zr2Ni (Al2Cu) and the tetragonal Zr2Cu (MoSi2) structure. It is further assumed that an icosahedral short-range order of the melt is stabilized by the addition of elements like Hf, probably Y or by contamination with very small amounts of oxygen, thus leading to a reduced interfacial energy between the quasicrystals and the amorphous matrix and therefore to a lower nucleation barrier.

In bulk metallic glass forming alloys cooled close to the critical cooling rate for glass formation, the nucleation density is observed to be spatially inhomogeneous; in an amorphous matrix there are spherical clusters with a high density of nanocrystals. This is attributed to the combined effect of recalescence due to the heat of crystallization and the fact that in deeply undercooled liquids the nucleation rate increases with increasing temperature.

A linear stability analysis of the non-linear differential equations describing nucleation and growth reveals that in the early stages of crystallization, stability is determined by the temperature dependence of the nucleation rate. When the nucleation rate increases with increasing temperature, fluctuations are amplified, resulting in “hot spots” where both the nucleation rate and the growth rate are higher.

We present crystallization studies on Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit1) and on other alloys, where the (Zr,Ti) and (Cu,Be) contents, along the line in composition space connecting Vit1 and Zr46.8Ti8.2Cu7.5Ni10Be27.5 (Vit4), were varied. Results from x-ray diffraction (XRD), small-angle neutron scattering (SANS) and differential scanning calorimetry (DSC) are combined to describe the crystallization behavior of these alloys at deep undercooling. SANS gives evidence for decomposition and the formation of nanometer sized crystals below a critical temperature Tc, which varies drastically as a function of composition. When Tc intersects with the glass transition temperature Tg, changes in the crystallization behavior are observed by DSC and XRD. At annealing temperatures near Tg, XRD resolves quasicrystalline phases for all alloy compositions from Vit1 to Vit4. From 9Be nuclear magnetic resonance (NMR) experiments performed on Vit1 upon annealing, we obtain information about the electronic structure and volume fraction of Be containing crystalline and quasicrystalline phases.

The phase formation of a Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5alloy has been investigated upon cooling from the melt at different quenching rates as well as upon annealing of as-cast specimens. The different samples are characterized by x-ray diffraction, transmission electron microscopy and differential scanning calorimetry. Rapid quenching using the melt spinning technique results in amorphization. Slower cooling as realized upon copper mold casting leads to an icosaheadral quasicrystalline phase coexisting with a small amount of amorphous phase. The primarily formed quasicrystals have a grain size of about 1 νm. Upon annealing, the amorphous phase formed upon melt spinning precipitates quasicrystals in the first step of a series of transformations to the crystalline equilibrium compounds. The quasicrystals formed by annealing do not exceed a size of 5 to 10 nm.

This work reviews the basic aspects of an alternative thermal treatment of metallic glasses by Joule heating, which explores the heat produced by an electrical current flowing through samples. The advantages of this annealing method are discussed, and a brief description of available models in a variety of materials is given. The experimental procedures are discussed in detail, with emphasis in a new variant of Joule heating, known as “linear varying current Joule heating”. This method allows one to precisely monitor the structural transformations that take place during annealing, by interrupting the thermal treatment at any desired point, leading to samples with controlled micro and/or nanostructures. Some examples of Joule heating curves in novel bulk amorphous samples are shown, to illustrate the excellent perspectives of this annealing technique.

We provide direct experimental evidence for a non-random distribution of atomic constituents in Zr-based multi-component bulk metallic glasses using positron annihilation spectroscopy. The Ti content around the open-volume regions is significantly enhanced at the expense of Cu and Ni, indicating that Cu and Ni occupy most of the volume bounded by their neighboring atoms while Ti and Zr are less closely packed and more likely to be associated with open-volume regions. Temperature-dependent measurements indicate the presence of at least two different characteristic sizes for the open volume regions. Measurements on hydrogen- charged samples show that the larger open-volume regions can be filled by hydrogen up to a critical density. Beyond this critical density, local atomic-scale open-volume damage is created in the sample to accommodate additional hydrogen. The onset of this local damage in positron annihilation data coincides with the onset of volume expansion in X-ray diffraction data.

The magnetic properties of novel bulk glassy Nd60Fe30Al10 magnets around the transition to the paramagnetic state have been studied in order to understand the magnetic microstructure in these materials. Analyses of the critical behavior of the magnetic isotherms suggest a transition from a low field magnetic state to a ferromagnetic-like state upon the application of high enough magnetic fields. The ferromagnetic-like state is evidenced by a scaling of the magnetization curves with critical exponents λ=1.5(1), β=0.65(5), and TC=465 K. These results are consistent with the predictions for weak random magnetic anisotropy systems.

The effects of pre-charged hydrogen on various kinetic processes in a Zr-Ti-Ni-Cu-Be bulk metallic glass alloy were investigated. Hydrogen charging induced longer internal time scales for structural relaxation and viscous flow. Crystallization was retarded by hydrogen charging leading to enhanced glass stability. Positron annihilation spectroscopy indicated reduced average free volume size after hydrogen charging. The reduced free volume and higher viscosity caused by hydrogen retard the plastic deformation and are believed to be responsible for hydrogen embrittlement.

The temperature dependencies of resistivity of the Ni-Pd-P-based amorphous alloys (P content was varied from 14 to 23 at. %) have been measured in a wide temperature range using the standard four-probe method. The temperature coefficients of resistivity (TCR) have been calculated. TCR value is decreased with P content increasing and becomes negative for Ni46Pd31P23 alloy. On the other hand, TCR value is increased with Pd content increasing while P content is not changed. Such behavior could be attributed to the electronic transfer effect from Ni to Pd and from P to Ni. These lead to the Fermi level shift to d-band edge and to the increasing influence of the Mott's localized state. The peculiarities caused by structural relaxation processes have been observed at the temperature range of 550 – 620 K. The relaxation process was shown to consist at least of two stages. The kinetics of the crystallization process has been analyzed using the Kissinger method.

The recent innovations in metallic glasses have led to new alloy classes that may be vitrified and a re-examination of the commonly used criteria for glass formation and stability. The new alloy classes are usually at least ternary systems and often higher order that can be grouped into two general categories. In one case large, bulk volumes may be slowly cooled to the glassy state which signifies a nucleation controlled synthesis. The other important class is represented by Al and Fe based glasses that can be synthesized only by rapid solidification processes such as melt spinning. These glasses are often called marginal glass formers that are synthesized under growth controlled kinetic conditions. With marginal glass forming alloys the termination of the amorphous state upon heating is often not characterized by a clear glass transition signal, Tg, but instead by the rapid onset of a primary crystallization reaction that represents the partial crystallization into a high number density of nanocrystals of the major component (i.e. Al or Fe) dispersed within a residual amorphous matrix. However, a closer examination by modulated or dynamic differential scanning calorimetry (DDSC) has identified a true reversible Tg signal that confirms the amorphous state and has revealed additional low temperature annealing behavior that impacts the overall thermal stability and microstructure evolution. At the same time alternate synthesis strategies involving deformation alloying by intense cold rolling reveals that the primary crystallization reaction can be bypassed. Alternatively other approaches have demonstrated that by suitable alloying it is possible to innoculate the primary crystallization reaction and increase the density of primary nanocrystals by about an order of magnitude. These developments represent a major level of microstructure control that have an impact on the structural performance and stability.

Different bulk glass forming alloys in the neighborhood of Zr52.5Cu17.9Ni14.6Al10Ti5 (Vit105) have been investigated by differential scanning calorimetry (DSC), x-ray diffraction (XRD) and small-angle neutron scattering (SANS). Along the Ti/Al line in composition space, Zr52.5Cu17.9Ni14.6Al10−xTi5+x with – ≤ x ≤ +2.5, the glass transition temperature, Tg, and the undercooled liquid regime (the difference between the first crystallization temperature and the glass transition temperature) continually decrease with increasing x. SANS measurements of annealed alloys show interference maxima, giving evidence for decomposition on the nanometer scale, up to a critical temperature Tc. In contrast to Tg, Tc increases with x and thus intercepts with Tg in the range –2.5 ≤ x ≤ –1.25, depending on the time scale of the experiment. At this composi- tion, significant changes in DSC traces and XRD patterns are observed. Additional isothermal DSC experiments show that the onset times for crystallization are significantly different for temperatures below and above Tc. We conclude that Tc, respectively the relation between Tc and Tg, determines the crystallization behavior and the thermal stability of these bulk metallic glasses.

Crystallization of the Pd43Ni10Cu27P20 amorphous alloy during isothermal annealing in the undercooled temperature region is studied by electron microscopy and diffrential scanning calorimetry (DSC). It is established that different crystallization processes take place above and below the nose temperature of the time-temperature-transformation (TTT) diagram. Detailed analysis of the microstructural evolution at the early stages of the crystallization is performed. In addition, the stable phases in the Pd-Ni-Cu-P system are identified.

To increase toughness of a metallic glass with the nominal composition Zr57Nb5Al10Cu15.4Ni12.6, it was used as the matrix in the composites reinforced with W fiber, W particles, and W/Re particles. Microstructures of the composites are studied by scanning electron microscopy and electron microprobe. Compression results are presented. Dynamic deformation behavior of the composites is studied in ballistic tests. The tests were performed firing composite rods into 6061 T651 aluminum target and 4130 steel targets. The composite rods failed by localized adiabatic shear banding and exhibited self-sharpening behavior.