Automated methods for the quantification of 3D woven architectures

Serial sectioning was used to characterize the three-dimensional (3D) architecture of metallic textiles, a new class of periodic cellular materials for structural applications. Reconstructing the serial sectioned data required the development of an adaptive stitching algorithm to montage individual tiles from each section due to the sparse nature of this periodic structure where a predefined stitching pathway does not perform well. This dataset was used to develop computational tools to automate the quantification of the bonding efficiency and weave geometry to inform the weave processing as well as incorporate these parameters in the development of material models for more accurate performance prediction. An inverse correlation was present between the wire spacing and the bonding efficiency of wire joints where bonding efficiency increased with a decrease in wire spacing. These tools could have broader applications analyzing other periodic cellular materials, containing similar sized struts, utilizing different materials or processing routes

Grain boundary mobilities in polycrystals

International audienceMost metals, ceramics, semiconductors and rocks are composed of small crystals known as grains. When annealed, this polycrystalline structure coarsens, thus allowing the properties of a material to be tailored for a particular application. The mobility of grain boundaries is thought to be determined by the crystallography of the adjacent crystals, but experimental validation in bulk polycrystalline materials is lacking. Here we developed a novel fitting methodology by direct comparison of a time-resolved three-dimensional experimental data to simulations of the evolution of 1501 grains in iron. The comparison allows reduced mobilities of 1619 grain boundaries to be determined simultaneously. We find that the reduced mobilities vary by three orders of magnitude and in general exhibit no correlation with the boundary's five macroscopic degrees of freedom, implying that grain growth is governed by other factors

Effect of Hf alloying on magnetic, structural, and magnetostrictive properties in FeCo films for magnetoelectric heterostructure devices

Materials with high magnetoelectric coupling are attractive for use in engineered multiferroic heterostructures with applications such as ultra-low power magnetic sensors, parametric inductors, and non-volatile random-access memory devices. Iron–cobalt alloys exhibit both high magnetostriction and high saturation magnetization that are required for achieving significantly higher magnetoelectric coupling. We report on sputter-deposited (Fe0.5Co0.5)1−xHfx (x = 0 – 0.14) alloy thin films and the beneficial influence of Hafnium alloying on the magnetic and magnetostrictive properties. We found that co-sputtering Hf results in the realization of the peening mechanism that drives film stress from highly tensile to slightly compressive. Scanning electron microscopy and x-ray diffraction along with vibrating sample magnetometry show reduction in coercivity with Hf alloying that is correlated with reduced grain size and low film stress. We demonstrate a crossover from tensile to compressive stress at x ∼ 0.09 while maintaining a high magnetostriction of 50 ppm and a low coercive field of 1.1 Oe. These characteristics appear to be related to the amorphous nature of the film at higher Hf alloying