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In high-performance AlCu(Li)Mg aluminum alloys, Guinier–Preston–Bagaryatsky zones frequently form upon thermal ageing and play an important role in hardening the alloys. Here we report a novel type of highly-symmetric Guinier–Preston–Bagaryatsky zones formed in a high Cu-content AlCuMg alloy. Using atomic-resolution electron microscopy and first-principles calculations, we precisely characterized their morphology and structures. It is shown that these precipitates undergo three stages of structural and compositional evolution, leading to formation of these tetragonal-prism-like one-dimensional precipitated crystals and their early-stage precursors. [ABSTRACT FROM AUTHOR]

Abstract: Developments of high-strength aluminum alloys have always faced a difficult problem: owing to their small size, the early-stage strengthening precipitates are difficult to characterize in terms of composition, structure and evolution. Even for the widely used AlCuMg alloys, in which the phenomenon of precipitation hardening in metals was first discovered by Wilm more than a century ago, the essential questions remain: how many different precursors exist for the most effective strengthening precipitates (referred to S-phase), and how do they transform to the S-phase? Here we employ atomic-resolution electron microscopy imaging and first-principles energy calculations to address these problems. Our study demonstrates that the early-stage S-phase precipitates are highly dynamic in both composition and structure. Having their own genetic double Cu–Mg atomic walls to guide their evolution, these dynamic precipitates initiate, mature and grow with thermal aging following three evolution paths, leading to the S-phase precipitates formed, without exception, with even numbers of Cu–Mg atomic layers. [Copyright &y& Elsevier]

Y2(1-x)Gd2xSiWO8?:?A (0=x=1; A=Eu3+, Dy3+, Sm3+, Er3+) phosphor films have been prepared on silica glass substrates through the sol-gel dip-coating process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscope (AFM), scanning electron microscopy (SEM) and photoluminescence spectra as well as lifetimes were used to characterize the resulting films. The results of the XRD indicated that the films began to crystallize at 800 °C and crystallized completely at 1000 °C. The AFM and SEM study revealed that the phosphor films, which mainly consisted of closely packed grains with an average size of 90-120 nm with a thickness of 660 nm, were uniform and crack free. Owing to an efficient energy transfer from the WO42- groups to the activators, the doped lanthanide ion (A) showed its characteristicf-ftransition emissions in crystalline Y2(1-x)Gd2xSiWO8 (0=x=1) films. The optimum concentrations for Eu3+, Dy3+, Sm3+, Er3+ were determined to be 21, 5, 3 and 7 mol % of Y3+ in Y2SiWO8 films, respectively. The above lanthanide ions showed higher emission intensity for 02(1-x)Gd2xSiWO8 films. [ABSTRACT FROM AUTHOR]

Polycrystalline VOx thin films were grown on Si substrates by ion beam sputtering deposition and annealing in oxygen atmosphere, which were prepared for thermal-sensitive material of far infrared (IR) sensors. As the deposition temperature (∼150 °C) is lower compared to that (∼400 °C) used to deposit single phase of VO2, scanning electron microscopy (SEM) morphology indicates that the as-deposited vanadium oxide (VOx) thin films were very smooth in surface and their grains are not able to be resolved. After annealing at higher temperature, the thin films were grown finally into ball-like and skeleton-like grains. The four-probe test presents their sheet resistance and the temperature coefficient of resistance (TCR) of the VOx thin film, which are 50 kΩ/⧠ and -0.021 K-1 at 30 °C, respectively. In addition, IR absorption in the range of 2–20 μm has been characterized. [Copyright &y& Elsevier]

Polycrystalline VOx thin films that were prepared for thermal-sensitive material of far infrared sensor had been deposited on Si substrates by ion beam sputtering deposition. Scanning electron microscopy images indicated that VOx thin films (oxygen pressure of 1.5×10-3 Pa) were grown into compact and ultra-fine grains (⩽50 nm), the film surfaces seemed smooth and uniform. Four-point probe measurements showed that the homogeneity of the films was better than 98% in a size of 30×30 mm2. The four-point probe measurement on hot plate presented the sheet resistance and the temperature coefficient of resistance of the VOx thin film that were 50 kΩ/square and -0.021 K-1 at 28°C, respectively. In addition, some samples annealed in Ar atmosphere had their resistance decreased. Thus, vanadium oxide films containing more amount VO2 were obtained. [Copyright &y& Elsevier]

Abstract: The S-phase is one of the key strengthening precipitate phases in high-strength 2xxx (AlCuMg) aluminum alloys. Nonetheless, the crystal structure of the S-phase remains controversial, and therefore its physical properties are almost unknown. Using atomic-resolution imaging in electron microscopy and first-principles energy calculations, it was confirmed at last that the structure model proposed by Perlitz and Westgren in 1943 is the only right model for well-developed S-phase precipitates. The structure model proposed by Perlitz and Westgren in 1943 is the only right model. Detailed calculations analysis of the S-phase structure reveals that the characteristics of Cu–Mg bonding and Cu–Al bonding in the structure are basically metallic, but with an ionic character due to electron charge transfer between atoms, leading to a large elastic modulus for the S-phase precipitates to strengthen AlCuMg alloys. [Copyright &y& Elsevier]

Abstract: Precipitate volume fraction is an important parameter to estimate the strength of precipitation-hardened metals. In this study, a facile method was applied to measure the precipitate volume fractions in an age-hardened AlCuMg alloy. In this method, the precipitate volume fraction values can be obtained by multiplying the volume precipitate number densities with the averaged precipitate volumes, which can be easily measured in scanning electron microscopy and transmission electron microscopy, respectively. Compared with the conventional method, in which the specimen thickness has to be measured in transmission electron microscopy, the method proposed in this study is more facile to perform. [Copyright &y& Elsevier]