Conditions near a crack tip: Advanced experiments for dislocation analysis and local strain measurement

The local stress state and microstructure near the crack-tip singularity control the fracture process. In ductile materials multiple toughening mechanisms are at play that dynamically influence stress and microstructure at the crack tip. In metals, crack-tip shielding is typically associated with the emission of dislocations. Therefore, to understand crack propagation on the most fundamental level, in situ techniques are required that are capable to combine imaging and stress mapping at high resolution. Recent experimental advances in x-ray diffraction, scanning electron microscopy, and transmission electron microscopy enable quantifying deformation stress fields from the bulk level down to the individual dislocation. Furthermore, through modern detector technology the temporal resolution has sufficiently improved to enable stress mapping during in situ experiments.

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Electrodeposition of Aluminum in the 1-Ethyl-3-Methylimidazolium Tetrachloroaluminate Ionic Liquid

The electrodeposition of Al was investigated in an ionic liquid (IL), with 1-ethyl-3-methylimidazolium tetrachloroaluminate ([EMIm]AlCl4) as the electrolyte with AlCl3 precursor. The [EMIm]AlCl4 electrolyte exhibited a wide and stable electrochemical window from 3.2 to 2.3 V on a glassy carbon electrode when temperature was increased from 30 °C to 110 °C. The addition of AlCl3 into [EMIm]AlCl4 generated significant well-developed nucleation growth loops, and new coupled reduction and oxidation peaks in cyclic voltammograms corresponding to the Al deposition and dissolution, respectively. A calculation model was proposed predicting compositions of anions in AlCl3/[EMIm]AlCl4 system, and [Al2Cl7]− was found to be the active species for Al deposition. In AlCl3/[EMIm]AlCl4 (1:5), the reduction rate constants were 1.18 × 10−5 cm s−1 and 3.37 × 10−4 cm s−1 at 30 °C and 110 °C, respectively. Scanning electron microscope (SEM), energy dispersive spectroscope (EDS), and X-ray diffraction (XRD) microscope results showed that the metallic Al film had been successfully deposited on glassy carbon electrodes through constant-potential cathodic reductions. The [EMIm]AlCl4 was a promising electrolyte directly used for Al deposition.

Development of an AlCl3-Urea Ionic Liquid for the Electroless Deposition of Aluminum on Carbon Nanotubes

Unlike the easy electroless deposition of other metals, the deposition of aluminum can be challenging. This is because the standard reduction potential of aluminum lies outside the electrochemical window (EW) of water. Ionic liquids such as AlCl₃-1-ethyl-3-methylimidazolium chloride (EMIC) have been used because of their wide EW. Here, we introduce a novel ionic liquid for electroless deposition of aluminum by reacting AlCl₃ and urea, with lithium aluminum hydride (LAH) as a reducing agent. Additionally, we report the first successful effort in coating carbon nanotubes (CNTs), as an example of nanostructures with high surface area to volume ratio, with aluminum using electroless deposition. The produced aluminum coating was found to be nanostructured, uniformly covering the CNTs and in close contact with their surfaces.

High density of genuine growth twins in electrodeposited aluminum

We demonstrate electrodeposition as a synthesis method for fabrication of Al coatings, up to 10 μm thick, containing a high density of genuine growth twins. This has not been expected since the twin boundary energy of pure Al is very high. TEM methods were used to analyze deposited Al and its nanoscaled twins. DFT methods confirmed that the influence of the substrate is limited to the layers close to the interface. Our findings are different from those achieved by sputtering of Al coatings restricted to a thickness less than 100 nm with twins dominated by epitaxial effects. We propose that in the case of electrodeposition, a high density of twins arises because of fast nucleation and is additionally promoted by a monolayer of adsorbed hydrogen originating from water impurities. Therefore, electrodeposition is a viable approach for tailoring the structure and properties of thicker, deposited Al coatings reinforced by twins.