The properties of materials change, sometimes catastrophically, as alloying elements and impurities accumulate preferentially at grain boundaries. Studies of bicrystals show that regular atomic patterns often arise as a result of this solute segregation at high-symmetry boundaries, but it is not known whether superstructures exist at general grain boundaries in polycrystals. In bismuth-doped polycrystalline nickel, we found that ordered, segregation-induced grain boundary superstructures occur at randomly selected general grain boundaries, and that these reconstructions are driven by the orientation of the terminating grain surfaces rather than by lattice matching between grains. This discovery shows that adsorbate-induced superstructures are not limited to special grain boundaries but may exist at a variety of general grain boundaries, and hence they can affect the performance of polycrystalline engineering alloys.

The ex situ lift out (EXLO) adhesion forces are reviewed and new applications of EXLO for focused ion beam (FIB)-prepared specimens are described. EXLO is used to manipulate electron transparent specimens on microelectromechanical systems carrier devices designed for in situ electron microscope analysis. A new patented grid design without a support film is described for EXLO. This new slotted grid design provides a surface for holding the specimen in place and also allows for post lift out processing. Specimens may be easily manipulated into a backside orientation to reduce FIB curtaining artifacts with this slotted grid. Large EXLO specimens can be manipulated from Xe+ plasma FIB prepared specimens. Finally, applications of EXLO and manipulation of FIB specimens using a vacuum probe lift out method are shown. The vacuum probe provides more control for placing specimens on the new slotted grids and also allows for easy manipulation into a backside configuration.

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Ni-23at%W thin films were ion-beam machined and tested in bending. Microstructures were characterized with aberration-corrected electron microscopy and the fracture surfaces were inspected after each test with SEM. Nominally amorphous films fractured along oxide streaks that formed during deposition. Heat treating at 700 °C crystallized the samples to a grain size of 30 nm, and the corresponding fracture toughness increased from 2.1 to 2.5 MPa√ . This work demonstrates that mesoscale features and impurities influence amorphous and nanocrystalline Ni-W fracture.Nanocrystalline metals formed from alloys such as Ni-W often offer attractive mechanical properties such as high hardness, but high strength is frequently accompanied by poor fracture toughness [1]. Unfortunately, reliable toughness information is limited because the small number of publications that report on the fracture of nanocrystalline metals indicate (1) that quantitative toughness measurements are challenging to conduct [2], and (2) that the toughness and fracture morphology may be functions not only of composition, pore size, and grain size, but also of mesoscopic features such as nanograin colony size [3]. Quantitatively determining fracture toughness of nanocrystalline metals remains a particular challenge because many such materials are thin films [4,5]. Conventional macro-scale tensile tests or hardness indentation measurements are generally neither feasible nor effective [6]. Likewise, analysis of structure and chemistry at a level sufficient to provide a complete description of the fracture process may require specialized characterization tools that are not widely available. As a result, very few studies have successfully conducted quantitative fracture toughness evaluation with detailed analysis of the links between toughness, microstructure, nanostructure, and localized chemistry.Micro-scale cantilever beam testing provides one viable approach to quantitative toughness measurement [7,8]. It allows the isolation of a nanocrystalline thin film from its substrate and the selection of small defect-free regions to avoid large cracks or pores. In addition, proper selection of specimen preparation and testing conditions allows the use of linear © 2015. This manuscript version is made available under the Elsevier user license

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