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.

In this work, a novel process is described for the fabrication of multi-metallic amorphous metal alloy coatings using a chemical vapor deposition (CVD) technique. Of special interest in this work are amorphous metal alloys containing Mo and/or Cr which have high crystallization temperatures and readily available low decomposition temperature metal-bearing precursors. The conditions for amorphous alloy formation via CVD are described as well as the chemical properties of these materials. High temperature, aqueous corrosion tests have shown these materials (especially those containing Cr) are among the most corrosion resistant metal alloys known.

Metal/ceramic bilayers fracture by one of three failure modes; crazing, spalling or interfacial failure. Models for these failure modes are developed. The results are presented as maps that can be used in the design and failure analysis of electronic packages. Examples are presented for several material systems, including A1N.

The corrosion resistance of Cr-based amorphous metal alloys at high temperature in concentrated acidic solutions of commercial interest was examined. Direct corrosion measurements and surface studies indicate that in binary, amorphous CrX alloys, their chemical stability is a strong function of the identity of the X component. The X = P, N, As and C samples are the most stable having excellent corrosion resistance to both oxidizing and reducing acidic solutions. Corrosion occurs in these materials at high temperature (> 90°C) in concentrated HCl solutions. The X = Si, Al and B samples are stable in mildly oxidizing solutions like H2SO4 and unstable in strongly reducing solutions like HF. Their chemical properties are dominated by the formation of a mixed oxide surface (Cr-silicate, Cr-aluminate, and Cr-borate) upon exposure to aqueous solutions. The X = Sb amorphous alloys did not passivate in any of the test solutions of this study. The nature of the passive layer and the passivation process is discussed for Cr-based amorphous alloys. At high temperatures, many of the CrX amorphous alloys exhibit a transition from a passive to an active corrosion state. Additions of Mo and Ta to the CrX amorphous alloys further improvement their corrosion resistance by increasing the temperature of this transition.

The addition of noble metals to Cr-based amorphous alloys can dramatically improve their corrosion resistance. The results of x-ray photoemission spectroscopy and cathodic polarization measurements show that the noble metals concentrate on the surface of the alloys and affect both the cathodic and anodic reaction kinetics. The amorphous Cr alloys require far less noble metal content to provide corrosion resistance in HCl compared to the corresponding crystalline Cr alloys. This allows the development of amorphous Cr alloys that are extremely stable in both reducing and oxidizing acids at high temperatures.

Magic angle spinning 29Si nuclear magnetic resonance has been used to probe the short and medium range order in polycrystalline and glassy SiS2 and SiSe2. These measurements provide complementary information to the existing Raman, IR and diffraction data on these glasses and allow a quantitative comparison with the various proposed structural models for chalcogenide glasses. Three distinct Si-sites are observed which differ in their second near neighbor environments. These sites are the result of having edge-sharing and corner-sharing tetrahedral arrangements in the glassy network. A new structural unit is proposed that can satisfy both the new information available from this work and the previous optical and diffraction data.

Amorphous metal formation, corrosion resistance, and the electrochemical properties of CrSi alloys have been investigated and compared with previous results on CrB and other amorphous metal alloys. Amorphous metal alloys are formed by sputtering in the Cr100−xSix alloys for values of x > 25. These alloys are significantly more corrosion-resistant than crystalline chromium and they are extremely stable in a variety of chemical environments. This enhancement in corrosion resistance results from the addition of silicon as well as the formation of an amorphous phase. Measurements of the passive layer formed on the CrSi alloys indicate that the passive layer is relatively thin and composed of both chromium and silicon ions.

We propose that all ${A}_{1\mathrm{\ensuremath{-}}x}$${B}_{x}$ glasses [where A (B) is a late (early) transition metal] are structurally isomorphic, chemically random alloys which store hydrogen in tetrahedral interstitial sites ${A}_{4\mathrm{\ensuremath{-}}n}$${B}_{n}$ (in decreasing order n=4,3,2,. . . ). The maximum absorbed hydrogen-to-metal atomic ratio within each type of interstitial site is ${1.9(}_{n}^{4}$)${x}^{n}$(1-x${)}^{4\mathrm{\ensuremath{-}}n}$ [${(}_{n}^{4}$)=4!/n!(4-n)!] independent of alloy and temperature. The chemical potential as a function of hydrogen concentration within a single site type n is also independent of composition and temperature. The only nonuniversal feature is the dependence of the typical site energies ${E}_{n}$ of the type-n sites on the A and B atoms, which may, however, be estimated from crystalline hydride properties. This model agrees with our electrochemical measurements of hydrogen in Ni-Zr, Pd-Ti, and Ni-Ti, predicts total H/M ratios for Ni-Zr and Cu-Ti alloys in excellent agreement with literature gas-phase data over a wide range of compositions and thermodynamic conditions, and is consistent with literature H/M data on other alloys at isolated compositions. We show theoretically that infinite near-neighbor hydrogen-hydrogen interactions (blocking) in a glass dominated by fivefold rings of tetrahedral units predicts the observed x dependence of H/M with a prefactor of 1.9--2.1, in excellent agreement with the observed factor of 1.9. This result supports theoretical models of icosahedral ordering in glasses.