Monte carlo sampling for microsegregation measurements in cast structures
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I. INTRODUCTION
THE understanding of solidification microsegregation has great importance for process optimization, microstructure control, and ultimately the mechanical properties of the final products. There exist several experimental methods for the measurement of the segregation characteristics of an alloy. The most commonly known ones are planar directional solidification,[1,2] equilibrium solidification,[3] interrupt quenching,[4] dendrite contour mapping,[5] eutectic composition measurement,[6] and random mapping.[7] Planar directional solidification produces bar samples with the elemental segregation along the direction of crystal growth. The segregation profiles can be obtained by chemical analysis of slices cut off from different locations along the axis of the bar samples. Equilibrium solidification and the interrupt quenching retain the semisolid structure at the high temperature during solidification. Elemental partitioning coefficients are obtained by measuring the quenched solid and liquid composition using methods such as electron probe microzone analysis. Dendrite contour mapping employs the transverse sections of a directionally solidified structure. By measuring the composition on the transverse section, the method reconstructs the elemental distribution map to find the relation of segregation and the solid volume. In each of the first four methods, controlled solidification has to be exercised to get the microstructure desired for the measurement, which by itself has to be carried out at specific locations or orientations. The random sampling method was first proposed and used by Brody and Flemings.[8] Detailed description of the method
WANHONG YANG, Research Assistant Professor, and KEH-MINN CHANG, Professor, are with the Department of Mechanical and Aerospace Engineering, West Virginia University, WV 26506. WEI CHEN, formerly Graduate Research Assistant, Department of Mechanical and Aerospace Engineering, West Virginia University, is Materials Engineer, GE Power Systems, Schenectady, NY 12308. SARWAN MANNAN, MetallurgistAdvanced, Research & Development, and JOHN DeBARBADILLO, Manager, Special Projects, are with Special Metals Corporation, Huntington, WV 25705. Manuscript submitted January 6, 2000.
METALLURGICAL AND MATERIALS TRANSACTIONS A
can be found in Reference 7. The method utilizes a conventionally solidified microstructure. Microzone analysis methods such as scanning electron microscopy/electron dispersive spectrometry (SEM/EDS) or atomic probe are used for the determination of composition. The sampling points for chemical composition analysis are randomly located on a polished sample surface. The compositions from all the sampling points are sorted. A segregation profile in the solid can be obtained with respect to the volume fraction of solid formed during solidification. The advantages of the method are obvious over the other methods: no special solidification experiment is needed,[1–6] no predetermined sampling locations are required for composition sampling,[1,5] and, furthermo
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