Amorphous metallic powders can be formed by mechanical alloying in a high-energy ball mill. Starting from the elemental, crystalline powders, ball milling first produces powder particles with a characteristically layered microstructure. Further milling leads to an ultrafine composite in which amorphization by solid state reaction takes place. The glass-forming range has been determined in detail for Fe-Zr and Ni-Zr. In Fe-Zr it differs completely from rapidly quenched amorphous samples. A systematic study of alloys of 3d transition metals with Zr and Ti shows that the glass-forming ability depends critically on a large negative free enthalpy of mixing. The results lead to the conclusion that amorphization by mechanical alloying is based on a solid state reaction and occurs under a metastable thermodynamic equilibrium neglecting the existence of intermetallic phases. Measurements of the superconducting transition temperature and Möβbauer studies show the structural similarity of mechanically alloyed and rapidly quenched amorphous samples. Finally mechanical alloying of FeZrB and NdFeB is described. Whereas FeZrB becomes amorphous after an additional annealing, a microcrystalline powder with very high coercivity is formed for NdFeB.

The classical formation of metallic glasses by rapid quenching requires the suppression of the nucleation and growth of crystalline phases during cooling from the liquid alloy melt. More recently a variety of techniques have been described in the literature wherein amorphous metal alloys have been prepared by diffusion reactions under solid state conditions. These include hydrogen glass forming reactions, multilayer diffusion couples, and mechanical alloying.

Wet chemical and thermal synthetic methods are described which allow the preparation of a wide variety of multi-component amorphous metal alloy precursors. Subsequent heat-treatment of these precursor materials serves to transform them into a substantially amorphous metal alloy powder. In the parent process, at least one metal-bearing compound is disposed in a liquid medium then reduced so as to obtain an intimate molecular mixture of the elements of the amorphous metal alloy to be synthesized. Specific examples of typical reduction procedures and variations are included. The modification of the chemical reaction schemes with respect to the parent process will be addressed in terms of the variability of intermediate precursor mixtures that can be isolated. In all cases, the critical step for the production of the amorphous metal alloy is the synthesis of a homogeneous, intimate mixture in the precursor powder. The solid-state reaction which occurs to alloy this intimate mixture is discussed in terms of the relative free energy difference between the intimate mixture and the resultant amorphous alloy.

The deviations from local equilibrium at a rapidly moving solid-liquid interface are well documented. The fraction of solute atoms in the liquid at the interface that joins the crystal during rapid solidification approaches unity and the interface temperature drops. Experimental and theoretical work on impurity incorporation and interfacial undercooling is reviewed. Past and future experiments to test the theories are discussed.

Real-time techniques were used to study rapid melt and solidification dynamics in silicon. In crystalline Si, the interface response function was characterized and found to be asymmetric for large deviations from the melting temperature, which will require reevaluation of conventional transition state treatments of melt and solidification. In amorphous Si, the mechanism of explosive crystallization was studied. The explosive transformation is mediated by a buried liquid layer, and detailed measurements have led to the suggestion that polycrystalline Si nucleates at the moving liquid-amorphous interface. For certain conditions, this process could yield fine-grained polycrystalline Si; for other conditions it permits epitaxial regrowth from the underlying crystalline Si for maximum melt thickness much less than the original amorphous layer thickness.

We report measurements of interdiffusion in compositionally modulated amorphous Ni-Zr films. We show the dependence of the diffusion coefficient on the modulation wavelength and correlate it with the thermodynamic properties of the Ni-Zr system. A bulk interdiffusion coefficient is extrapolated from the data. Our values for the interdiffusivity in Ni55Zr45 are about three orders of magnitude lower than those obtained by other authors for similar alloys. Possible explanations are suggested.

Interdiffusion and structural relaxation in amorphous compositionally modulated films of Fe-Ti have been measured simultaneously. Interdiffusivity is determined by the change in X-ray modulation peak intensity upon annealing and structural relaxation is determined by the shift in X-ray peak position corresponding to the densification. The relaxation kinetics of the densification are explained by the free volume model of structural relaxation. The relaxation kinetics of the inverse diffusivity are shown to be the same as for viscosity relaxation.

Mechanical alloying (MA) of iron, cobalt, and nickel with titanium and also with samarium produces a continuous growth of an amorphous phase. X-ray diffraction analyses show that the growth of the phase is described by a square root of time law. Differential scanning calorimetry data also confirm that mechanically alloyed powders are amorphous. Dry MA and MA in the presence of toluene are compared. The rate of alloying is much higher in the presence of toluene. Amorphous powders re-alloyed with the fast diffuser are consolidated by means of extrusion.

In the HVI process, alloys are arc-melted in a watercooled copper crucible and injected (at high velocities) into a circular channel by a gas/vacuum coupled pressure gradient. The molten jet rapidly solidifies, as it is in good thermal contact with the circular walls of the copper channel. This process (melting and injection) is carried out in the inert protective atmospheres (helium). The samples produced are in the form of cylindrical rods with large length to diameter ratios (40:1). The samples exhibit a good surface finish and are of high density. Results presented in this paper show that amorphous samples can be produced using the HVI process.

Crystalline particles and grains embedded in Cu35Ti65 glass ribbons have been amorphized by isothermal cold rolling. The structural evolution has been studied by X-ray diffraction and TEM techniques. Initial particle morphologies are spherulitic and spherical, the latter with sizes ranging between 10 and 100 nm. The new amorphous phase seems to nucleate at crystalline-amorphous matrix interfaces. Initially there is a well defined interface between the new and the existing amorphous phases but it disappears as rolling progresses. Crystallites on a nanoscale still present in the final stages of particle amorphization have been observed by convergent beam electron diffraction. After sufficient deformation the consolidated ribbon becomes completely glassy. A morphological description of the transformation process in terms of crystal destabilization and solid-state particle melting is presented.

We have investigated the formation of amorphous and microcrystalline alloys of Pd-Si and Ti-Pd. In order to allow comparison of the two methods, both liquid quenching (LQ) for rapid solidification and mechanical alloying (MA) techniques were employed. Characterization of the materials was obtained through X-ray diffraction and differential thermal analysis (DTA).

Both the LQ and MA syntheses yielded amorphous Pd80Si20 alloys, with very similar X-ray line widths and crystallization temperaiures. However, the MA alloys contained as minority component a second phase, indexed to Pd3Si.

Quite different results were obtained for the Ti-Pd alloys. LQ splats containing 42, 66, and 80 at % Ti were not amorphous but microcrystalline, as might be expected from the very similar atomic radii of Ti and Pd. In contrast, a broad range of amorphicity, from approximately 42 to 85 at % Ti, was found in the MA synthesized materials. Overall, these results show that the two methods, LQ and MA, differ in the mechanisms of amorphization. This conclusion is further supported by additional MA and LQ experiments on ternary Ti-Pd-Cu alloys.

The amorphization reaction in mechanically prepared metallic Ni-Zr composites has been investigated by X-ray diffraction, electrical conductivity and magnetization measurements during isothermal annealing. The formation kinetics of the amorphous phase are determined by the diffusion of the Ni atoms across the amorphous NiZr layer. The diffusivity of Ni atoms in the initially formed amorphous Ni58.5 Zr41.5 is measured in the temperature range from 225°C (Dni= 5.3×10−17 cm2/sec) to 325°C (Dni= 1×10−14 cm2/sec). The data fit an Arrhenius plot with an activation energy of 1.4 eV. Magnetic coercivity measurements indicate that neither recovery nor recrystallization occurs in the Ni layers during the reaction. The Kirkendall effect caused by the anomalous fast diffusion of Ni is directly monitored by dilatometric measurements. Microhardness results are also presented. The role of a diffusion-related growth selection favoring the amorphous phase is critically assessed with respect to the glass formation.

Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) measurements were performed on a-Zr2 PdHx, a-Zr3 RhHx, a-Zr76 Fe24 Hx, and a- Zr2NiHx to assess the effects of hydrogen on their thermal stabilities. Only exothermic DSC peaks were observed for the hydrogen-free glasses and are shown to correspond to the formation of crystalline intermetallic phases. On the other hand, heating of the amorphous hydrides gives decomposition reactions with the generation of ZrHx (1.5 <x < 2.0) and either free metal (e.g., Rh) or a Zr-depleted intermetallic (e.g., ZrPd). With the exception of the Zr2 PdHx samples, hydrogenation significantly decreases the thermal stabilities (i.e., the exothermic transitions occur at lower temperatures in the amorphous hydrides). Endothermic peaks, which are associated with hydrogen evolution from the glass, are observed when the hydrogen-to-metal ratios approach unity.

Anodic dc polarization measurements of glassy Mg70 Zn30 in pH=9.3 boric-borate electrolyte with and without the presence of Cl− were used to study both passive film formation and breakdown. In the absence of C− a single, broad passivation peak is observed which is very similar to that found with triply distilled Mg except that the large increase in peak potential and reduction in peak current density indicates that a more stable film has formed on Mg70 Zn30. Also observed with Mg70 Zn30 but not with Mg, Zn or other different types of crystalline Mg alloys is a large, narrow peak in the transpassive region (i.e., the region where the passive film begins to break down and/or O2 evolution commences). This process of breakdown of the passive film and further oxidation of the base metal is totally irreversible and is almost completely missing on the second and subsequent voltage sweeps. Although speculative in nature, existing evidence suggests that a phase transition has occurred within the passive film itself. In the presence of Cl− this process does not occur as passive film breakdown is initiated via a pitting mechanism at a potential nearly 2.5 Volts more negative than the onset of O2 evolution. Nevertheless, the onset of pitting is still 0.4 Volts more positive than that found for Mg indicating again that a much more protective film has formed on Mg70 Zn30

Several samples of consolidated amorphous alloys have been studied by using High Resolution Electron Microscopy (HREM), Differential Scanning Calorimetry (DSC), Microdiffraction (MD), and Energy Dispersive X-Ray Diffraction Analysis (EDXD). The phenomenon of plastic deformation at consolidated particulate interfaces has been examined. Two simultaneous processes have been identified occurring at these boundaries, namely, accelerated nucleation and growth of the deformed zone and the the formation of dislocation microstructures (dislocation networks). It has been observed that both type and the density of microstructures depend on the mode of consolidation. Post consolidation processing, annealing, affects density and the directional distribution of defects in the plastic zone. Microstructural examination of the consolidated mass has revealed two major factors important in the strengthening mechanism: (1) presence of a plastically deformed and pressureinduced nucleated zone; (2) presence of a system of dislocation networks in the compacted particulates. Based on these observations, it has been concluded that the stored strain energies in the plastically deformed zones provides the necessary activation energy for dislocation motions from one particulate to the next. These observations have been employed in developing a quasi-quantative model to explain the strengthening mechanism in consolidated amorphous alloys.

Microadditions of cerium retard annealing embrittlement in some but not all metallic glass compositions in the FeBSi system. Effects on embrittlement of doping with both cerium and oxygen have been determined for a series of compositions, FexB13 Si87-x. For X > 80, cerium retards annealing embrittlement and oxygen promotes it, suggesting that the beneficial effect of cerium additions results from gettering of impurities. The results indicate that for those compositions in the FeBSi system with the highest values of the saturation magnetization, Ms, microadditions of cerium can prevent annealing embrittlement until the onset of crystallization.

Measurements have been made of the corrosion and fatigue properties of metallic glass wires of composition Fe75-xCrxB15Si10 (X = 5, 8, 11) in air, deionized water, 3.5 w/o NaCl and 1.0 N H2SO4. A clear inverse relationship was observed between the corrosion rate and the number of cycles to failure. Fatigue limits were observed for those cases where spontaneous passivation occurs (all compositions in air and deionized water, and 8 and 11 a/o Cr in chloride solution). It was found that the mechanism for the fatigue failure of specimens which spontaneously passivate differs from that of metallic glasses in an acidified chloride environment where active/passive behavior is observed. A model is proposed to explain this observation.

We have studied a number of binary metal-metal and metalloid alloy systems made by a single vapor quench method under very consistent conditions. In each case, amorphous alloys are found in one continuous composition range (Xmin<x<xXmax) regardless of the number of eutectic points in the equilibrium phase diagrams. It is found that the atomic size difference is the single most important factor in the quantitative determination of the composition range.

The ferromagnetic transition temperature Tc for Fe-Si-B amorphous alloys with iron concentration exceeding 75 atomic percent changes monotonically with the annealing time. This change of Tc is accompanied by a drastic change of the magnetic excitation spectrum measured by means of low angle neutron inelastic scattering. It was observed that a small amount of α-Fe(Si) precipitated in an amorphous matrix during the heat treatment even at relatively low temperatures, leading to a decrease of the spin-wave stiffness constant D. Because at the same time T, increases, the D/Tc ratio (which is about 0.3 for “as quenched” Fe-Si-B system) decreases abruptly.

An Ni44 Fe32Cr11P8B5 (at.%) alloy was sputter deposited on to water cooled 304 stainless steel substrates. Electrochemical testing was performed in 0.1N H2So4 with and without the addition of O.06N NaCI. The surface layers of specimens polarized into the active and passive regions of the anodic polarization curves were analyzed using x-ray photoelectron spectroscopy (XPS) to check for preferential dissolution and possible segregation of the constituent elements. A significant improvement in the overall corrosion behaviour of 304 stainless steel was observed due to the sputter deposited layer.

Gas atomization is one of the key processes used for the production of rapidly solidified materials. The unique feature of the gas atomization process is its capability to form spherical powders of multicomponent alloys containing reactive elements. Spherically shaped powder is specified in the secondary processing operations used in a number of applications. This requirement has resulted from the higher flow rate, better packing density, and lower surface area obtained in spherical particles compared to irregularly shaped particles.