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Understanding the impact of thermo-solutal convection during alloy solidification is of central importance in the casting industry. Convective flow generated from density variations in the liquid is at the origin of many casting defects, such as chemical segregations and freckles, to which Ni-based superalloys used in jet engines are known to be highly sensitive. In this article, we present experimental results obtained during directional solidification of a CMSX-4 single crystal superalloy observed in-situ by means of synchrotron X-radiography at the European Synchrotron Radiation Facility (ESRF, Grenoble, France). The use of a high-temperature directional solidification furnace, an intense monochromatic beam and a high-speed X-ray sensitive camera allowed the direct observation of the development of solute flow to be performed during dendritic growth of a Ni-based alloy. The transient stage leading to the formation of a dendrite network and the interaction with the concomitantly developing convective pattern are studied. The impact of solute flow on the dendrite growth velocity is characterized for three cooling rates. Measurements of dendrite tip positions show that the convective flow above the solidification front induces a periodic oscillation of the dendrite growth velocity and that the oscillation amplitude decreases for higher cooling rates. The development of residual liquid areas is observed on the sides of the sample. Fragmentation of dendrite parts occurs during the solidification of the residual liquid areas and leads to the formation of spurious grains. The experimental results are analyzed by using a Rayleigh number-based model, highlighting the need for direct simulations in the future. Image, graphical abstract [ABSTRACT FROM AUTHOR]

One of the challenges encountered in the industrialization of new single-crystal superalloys parts (like high-pressure turbine blades and vanes for aircraft engines) is to limit the mechanical stresses during the solidification and cooling of the metal. In order to accurately predict the viscoplastic flow as well as the thermo-mechanical behaviour of Ni-based superalloy during its cooling, in this study a thermodynamically-consistent thermo-elasto-viscoplastic model was developed. This model takes into account the solid-liquid transition occurring in the material during the cooling phase. This is done by introducing a compressible-type viscoplastic yield function based on appropriate equivalent stress depending on volume fraction of the solid phase formed by the propagation of dendrites inside the liquid phase of the material. This model was implemented in Abaqus/Standard© F.E. code and applied to the identification of material parameters of Ni-based superalloy using isothermal tensile-relaxation tests driven for different strain rates and temperatures. First, anisothermal tensile-compression test was simulated on a single integration point. A comparison of the experimental and numerical stress-strain response partially validate the model. Second, a benchmark test involving casting of a rectangular Ni-based superalloy bar in a sand mold was simulated and analyzed. [ABSTRACT FROM AUTHOR]

Abstract: The current study tested a psychosocial interactive model of perfectionism, self-efficacy, and weight/shape concern within a sample of women with clinically significant bulimic symptoms, examining how different dimensions of perfectionism operated in the model. Individuals with bulimia nervosa (full diagnostic criteria or subthreshold) completed measures of bulimic symptoms, multidimensional perfectionism, self-efficacy, and weight/shape concern. Among those who were actively binge eating (n=180), weight/shape concern was associated with binge eating frequency in the context of high perfectionism (either maladaptive or adaptive) and low self-efficacy. Among those who were actively vomiting (n=169), weight/shape concern was associated with vomiting frequency only in the context of high adaptive perfectionism and low self-efficacy. These findings provide support for the value of this psychosocial interactive model among actively binge eating and purging samples and for the importance of considering different dimensions of perfectionism in research and treatment related to bulimia nervosa. [Copyright &y& Elsevier]