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Abstract: In this paper, we describe an on-going effort to develop a thin film combinatorial method for identifying alloy compositions of potential interest as structural materials. To investigate this idea, compositionally graded Ti–Al thin films have been sputter deposited onto Si substrates, and the mechanical properties of the “library” of compositions are then probed using nanoindentation. This combinatorial method offers the possibility of rapidly varying the compositions and microstructures of alloys and quickly determining the compositions and microstructures of greatest interest for further development as bulk structural alloys. Nanoindentation experiments are used to extract the properties of the film so that the bulk properties of the material may be estimated. A new method for extracting the hardness of films on substrates from nanoindentation experiments has been developed and is applied to the compositionally graded Ti–Al thin films. Together with the nanoindentation data and a compositional analysis, we are able to establish a relationship between the hardness of the film and the composition. We discuss the results of these combinatorial experiments in connection with estimating the properties of bulk materials. [Copyright &y& Elsevier]

In this study, time-dependent plastic deformation of micropillars fabricated from low melting point metal Sn (~ 505 K) was investigated at room temperature. Size-dependent strength was first evaluated and creep tests were then performed on the micropillars having diameters of 1 and 5 μm. Sn pillars showed significant creep deformation, and creep rate was independent of pillar size. Creep stress exponent was determined to be ~ 1, and negligible effect of e-beam irradiation on creep rate confirmed that the lattice diffusion must be the predominant creep mechanism. Creep deformation of Sn micropillars, therefore, differs from the dislocation-climb based creep in bulk Sn. [ABSTRACT FROM AUTHOR]

Microstructural evolution of focused ion beam machined Mg nanopillars was investigated by in situ heating experiments in a transmission electron microscope. The dislocation loops generated by a Ga+ ion beam were annihilated at around half of the melting point of Mg. At a higher temperature (673K), the sublimation of Mg occurred due to the reduced stability of Mg under the vacuum environment. In the course of sublimation, the Ga-rich liquid was formed and stabilized the structural instability of moving solid–vapor interface. [ABSTRACT FROM AUTHOR]

Abstract: Indium columnar structures with diameters near 1μm were deformed by uniaxial compression at strain rates of approximately 0.01 and 0.001s−1. Defect density evolution in the nanopillars was evaluated by applying synchrotron Laue X-ray microdiffraction (μSLXRD) on the same specimens before and after deformation. Results of the μSLXRD measurements indicate that the dislocation density increases as a result of mechanical deformation and is a strong function of strain rate. These results suggest that the rate of defect generation during the compression tests exceeds the rate of defect annihilation, implying that plasticity in these indium nanostructures commences via dislocation multiplication rather than nucleation processes. This is in contrast with the behaviors of other materials at the nanoscale, such as, gold, tin, molybdenum, and bismuth. A hypothesis based on the dislocation mean-free-path prior to the multiplication process is proposed to explain this variance. [Copyright &y& Elsevier]

Abstract: Vertically aligned, cylindrical tin nanopillars have been fabricated via an electron beam lithography and electroplating method. Characterization by a non-destructive synchrotron X-ray microdiffraction (μSXRD) technique revealed that the tin nanostructures are body-centered tetragonal and are likely single-crystalline, or consist of a few large grains. The mechanical properties of tin nanopillars with average diameters of 920nm, 560nm, and 350nm were studied by uniaxial compression in a nanoindenter outfitted with a flat punch diamond tip. The results of compression tests reveal strain rate sensitivity for nanoscale tin deformation, which matches closely to the previously reported bulk tin values. However, unlike bulk, tin nanopillars exhibit size-dependent flow stresses where smaller diameter specimens exhibit greater attained strengths. The observed size-dependence matches closely to that previously reported for single-crystalline face centered cubic metals at the nanoscale. μSXRD data was used to compare the dislocation density between as-fabricated and deformed tin nanopillars. Results of this comparison suggest that there is no measurable accumulation of dislocations within deformed tin nanopillars. [Copyright &y& Elsevier]