Phase-field modeling of eutectic structures on the nanoscale: the effect of anisotropy

This is a post-peer-review, pre-copyedit version of an article published in Journal of Materials Science. The final authenticated version is available online at: https://doi.org/10.1007/s10853-017-0853-8A simple phase-field model is used to address anisotropic eutectic freezing on the nanoscale in two (2D) and three dimensions (3D). Comparing parameter-free simulations with experiments, it is demonstrated that the employed model can be made quantitative for Ag-Cu. Next, we explore the effect of material properties, and the conditions of freezing on the eutectic pattern. We find that the anisotropies of kinetic coefficient and the interfacial free energies (solid-liquid and solid-solid), the crystal misorientation relative to pulling, the lateral temperature gradient, play essential roles in determining the eutectic pattern. Finally, we explore eutectic morphologies, which form when one of the solid phases are faceted, and investigate cases, in which the kinetic anisotropy for the two solid phases are drastically different

Effective elastic properties and residual stresses in directionally solidified eutectic Al2O3/YAG/ZrO2 ceramics estimated by finite element analysis

International audienceEffective elastic properties and residual stresses were assessed in directionally solidified ternary eutectic ceramic, Al2O3/YAG/ZrO2, by finite element analyses. A 3D finite element model was generated from a CT scan, representative of the microstructure and with a similar volume fraction. Effective elastic properties were calculated by numerical homogenisation. They highlight a quasi-isotropic behaviour of the ternary eutectic ceramics. Despite the difficulties to measure the strain, the dispersion observed in the results and the limited reliability of the materials properties, the results constitute a step towards a better understanding of the material behaviour. Thermal residual stresses induced by the manufacturing were also evaluated. Tensile residual stresses in yttria-stabilised zirconia and compressive residual stresses in YAG and alumina were highlighted. This evaluation also shed light on the influence of the phase morphology in the microstructure. Indeed, the computed spatial distribution of the residual stresses showed that they are different from one position to another due to the variation in phase morphology and also to material properties variability. Therefore, it is important when numerically assessing the thermomechanical properties to take into account the microstructure morphology as well as the variability of material properties

Boron isotope variability related to boron speciation (change during uptake and transport) in bell pepper plants and SI traceable n ( 11 B)/ n ( 10 B) ratios for plant reference materials

Rationale Boron (B) is an essential micronutrient in plants and its isotope variations are used to gain insights into plant metabolism, which is important for crop plant cultivation. B isotope variations were used to trace intraplant fractionation mechanisms in response to the B concentration in the irrigation water spanning the range from B depletion to toxic levels. Methods A fully validated analytical procedure based on MC‐ICP‐MS, sample decomposition and B matrix separation was applied to study B isotope fractionation. The validation was accomplished by establishing a complete uncertainty budget and by applying reference materials, yielding expanded measurement uncertainties of 0.8 ‰ for pure boric acid solutions and ≤ 1.5 ‰ for processed samples. With this validated procedure SI traceable B isotope amount ratios were determined in plant reference materials for the first time. Results The B isotope compositions of irrigation water and bell pepper samples suggest passive diffusion of the heavy 11B isotope into the roots during low to high B concentrations while uptake of the light 10B isotope was promoted during B depletion, probably by active processes. A systematic enrichment of the heavy 11B isotope in higher located plant parts was observed (average Δ11Bleaf‐roots = 20.3 ± 2.8 ‰ (1 SD)), possibly by a facilitated transport of the heavy 11B to growing meristems by B transporters. Conclusions B isotopes can be used to identify plant metabolism in response to the B concentration in the irrigation water and during intraplant B transfer. The large B isotope fractionation within the plants demonstrates the importance of biological B cycling for the global B cycle