Resampling technique applied to statistics of microsegregation characterization

Characterization of chemical heterogeneities at the dendrite scale is of practical importance for understanding phase transformation either during solidification or during subsequent solid-state treatment. Spot analysis with electron probe is definitely well-suited to investigate such heterogeneities at the micron scale that is relevant for most solidified products. However, very few has been done about the statistics of experimental solute distributions gained from such analyses when they are now more and more used for validating simulation data. There are two main sources generating discrepancies between estimated and actual solute distributions in an alloy: i) data sampling with a limited number of measurements to keep analysis within a reasonable time length; and ii) uncertainty linked to the measurement process, namely the physical noise that accompanies X-ray emission. Focusing on the first of these sources, a few 2-D composition images have been generated by phase field modelling of a Mg-Al alloy. These images were then used to obtain "true" solute distributions to which to compare coarse grid analyses as generally performed with a microanalyser. Resampling, i.e. generating several distributions by grid analyses with limited number of picked-up values, was then used to get statistics of estimates of solute distribution. The discussion of the present results deals first with estimating the average solute content and then focuses on the distribution in the primary phase

On the Deformation of Dendrites During Directional Solidification of a Nickel-Based Superalloy

Abstract: Synchrotron X-ray imaging has been used to examine in situ the deformation of dendrites that takes place during the solidification of a nickel-based superalloy. By combining absorption and diffraction contrast imaging, deformation events could be classified by their localization and permanence. In particular, a deformation mechanism arising from thermal contraction in a temperature gradient was elucidated through digital image correlation. It was concluded that this mechanism may explain the small misorientations typically observed in single crystal castings

Micromechanical Approach of the Fatigue Behavior in a Superelastic Single Crystal

Mechanical cycling of superelastic alloys leads to significant change in their observed behavior. Critical stress needed to induce the martensitic transformation is reduced while the tangent transformation modulus is increased. Microstructural observations have shown that a mechanical cycling produced a strongly oriented pattern of dislocations. This dislocation network is associated to an internal stress field. It seems reasonable to relate this internal stress field to the observed evolution of the mechanical response. This is phenomenologically performed in this work considering the thermodynamical potential associated to the martensitic transformation of a single crystal of parent phase in presence of a microstructure of defects. Evolutions of the microstructural state are defined using the volume fraction associated to the variant of martensite and additional volume fractions of defects related to the dislocation pattern. Results such obtained well-captured experimental observations

Relation between crystal quality and fatigue life of a Cu-Al-Be single crystal shape memory alloy under repeated bending.

The purpose of this study is to determine the parameters influencing the life of single crystalline Cu-Al-Be shape memory alloys. A strong correlation is found between crystal quality and fatigue life. For that purpose, a special device located at ILL (Institut laue-langevin) in Grenoble is employed. This device is a hard X-ray diffractometer using a transposition at high energy of the Guinier-Tennevin method. Thanks to these X-ray studies, it is found that mechanical lifespan is very sensitive to crystalline quality. In presence of sub-grains (even if disorientation between subgrain is lower than 3°) or in presence of mosaïcity (distribution of the orientation of reticular planes around a mean value), the lifespan can be reduce by a factor of 10

Relation between crystal quality and fatigue life of a Cu-Al-Be single crystal shape memory alloy under repeated bending.

The purpose of this study is to determine the parameters influencing the life of single crystalline Cu-Al-Be shape memory alloys. A strong correlation is found between crystal quality and fatigue life. For that purpose, a special device located at ILL (Institut laue-langevin) in Grenoble is employed. This device is a hard X-ray diffractometer using a transposition at high energy of the Guinier-Tennevin method. Thanks to these X-ray studies, it is found that mechanical lifespan is very sensitive to crystalline quality. In presence of sub-grains (even if disorientation between subgrain is lower than 3°) or in presence of mosaïcity (distribution of the orientation of reticular planes around a mean value), the lifespan can be reduce by a factor of 10