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Abstract: Synchrotron-radiation studies allowed continuous acquisition of X-ray diffraction spectra for binary Pd81Si19 bulk metallic glass forming alloy in the glassy, crystalline and liquid state. Such an investigation allowed determination of structural changes in the liquid and glassy states using real-space radial RDF(R) and atomic pair PDF(R) distribution functions. Crystallization behavior of this alloy was also studied by conventional X-ray diffractometry, transmission electron microscopy and differential scanning calorimetry in isochronal and isothermal mode. [Copyright &y& Elsevier]

Abstract: In situ vitrification in a synchrotron beam during cooling of a Pd42.5Cu30Ni7.5P20 melt allowed continuous acquisition of X-ray diffraction spectra in the supercooled liquid region between the liquidus temperature Tl and the glass transition temperature Tg for the first time in a metallic liquid alloy. These and subsequent acquisitions on reheating allowed determination of the structural changes in the supercooled and glassy states using the real space atomic pair distribution function PDF(R) and radial distribution function RDF(R). The nearest neighbor (NN) distance in the first coordination shell has a low R peak (pre-peak) that appears and increases on cooling from the liquidus temperature to the glass transition temperature in the supercooled liquid region. In this temperature range reversible expansion of the NN distances in the first coordination shell is observed. The slope of the expansion changes discontinuously at the glass transition. This behavior is explained by the theory of local topological fluctuations. [Copyright &y& Elsevier]

Abstract: (Zr0.55Al0.1Ni0.05Cu0.3)99Y1 bulk metallic glasses heavily deformed by cold rolling were studied by X-ray diffraction (XRD) in transmission using high energy monochromatic synchrotron radiation during in situ heat treatment. No crystalline grain was detected in the cold-rolled samples. After deformation, excess free volume, ΔV f, was measured by X-ray diffraction. In situ heating XRD results revealed that metastable crystalline phase was nucleated and grew before the formation of equilibrium CuZr2. Further investigation showed that the metastable phase is Zr3Al2-type crystalline structure which is the primary crystalline phase that appears in several Zr-based metallic glasses during the thermal treatment [Plappert R, Boström M, Kühn U, Vaughan G, Yavari AR, Kvick Å. ISMANAM, Paris; 2005]. [Copyright &y& Elsevier]

Due to its extremely short timescale, the non-equilibrium melting of metals is exceptionally difficult to probe experimentally. The knowledge of melting mechanisms is thus based mainly on the results of theoretical predictions. This work reports on the investigation of ultrafast melting of thin polycrystalline Pd films studied by optical laser pump – X-ray free-electron laser probe experiments and molecular-dynamics simulations. By acquiring X-ray diffraction snapshots with sub-picosecond resolution, we capture the sample's atomic structure during its transition from the crystalline to the liquid state. Bridging the timescales of experiments and simulations allows us to formulate a realistic microscopic picture of the crystal-liquid transition. According to the experimental data, the melting process gradually accelerates with the increasing density of deposited energy. The molecular dynamics simulations reveal that the transition mechanism progressively varies from heterogeneous, initiated inside the material at structurally disordered grain boundaries, to homogenous, proceeding catastrophically in the crystal volume on a picosecond timescale comparable to that of electron-phonon coupling. We demonstrate that the existing models of strongly non-equilibrium melting, developed for systems with relatively weak electron-phonon coupling, remain valid even for ultrafast heating rates achieved in femtosecond laser-excited Pd. Furthermore, we highlight the role of pre-existing and transiently generated crystal defects in the transition to the liquid state. [Display omitted] [ABSTRACT FROM AUTHOR]

Self-supporting porous silver foils with an average pore size < 100 nm were produced from a crystalline silver-based ternary alloy as a precursor by removing second phases present in the silver matrix. The final Ag-based porous foil shows good mechanical properties when comparing to its previous amorphous analogues. Its activity for direct electrochemical oxidation of ammonia-borane (AB), a fuel of interest for direct liquid fuel cells, has been investigated in alkaline media. The material exhibits promising electrochemical properties in long-term operation; indeed, material composition and nanostructure remain similar after 15,000 cyclic-voltammetries between − 0.3 and 0.5 V vs. RHE in a 0.1 M NaOH + 5 mM AB solution thermostated at 25 °C. Nanoporous materials, and in particular nanoporous silver, can therefore represent a relevant choice as anode in direct ammonia-borane fuel cell. [ABSTRACT FROM AUTHOR]

In present work we report the synthesis of nanoporous surface using a copper-based alloy via leaching the less noble element-rich phase out of nanostructured ternary Cu–Hf–Zr alloys. The removal of Hf and Zr by mixed acid etchants in the chill-zone region of rapidly solidified ingots leads to the formation of a nano-roughened surface layer constituted of copper. The average pore and grain size of the obtained structure were shown to be less than 100 nm and 50 nm respectively. [ABSTRACT FROM AUTHOR]