A procedure to create isoconcentration surfaces in low-chemical-partitioning, high-solute alloys
B C Hornbuckle1, M Kapoor1, G B Thompson1
1The University of Alabama, Department of Metallurgical and Materials Engineering, Tuscaloosa, AL, 35487 USA.
Abstract:
A proximity histogram or proxigram is the prevailing technique of calculating 3D composition profiles of a second phase in atom probe tomography. The second phase in the reconstruction is delineated by creating an isoconcentration surface, i.e. the precipitate-matrix interface. The 3D composition profile is then calculated with respect to this user-defined isoconcentration surface. Hence, the selection of the correct isoconcentration surface is critical. In general, the preliminary selection of an isoconcentration value is guided by the visual observation of a chemically partitioned second phase. However, in low-chemical -partitioning systems, such a visual guide is absent. The lack of a priori composition information of the precipitate phase may further confound the issue. This paper presents a methodology of selecting an appropriate elemental species and subsequently obtaining an isoconcentration value to create an accurate isoconcentration surface that will act as the precipitate-matrix interface. We use the H-phase precipitate in the Ni-Ti-Hf shape memory alloy as our case study to illustrate the procedure.
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