An ALCHEMI Investigation of Ternary Site Occupancy in NiAl-Based Alloys

Abstract

ALCHEMI, or atom location by channeling enhanced microanalysis, is a technique used for determining lattice site occupancies. Previously it has been applied to sublattice occupancy of trace elements in minerals and ternary additions to binary intermetallic compounds. Normally this is performed by acquiring spectra at both positive and negative deviations from the Bragg condition at a suitable plane. (Alternatively, spectra may be recorded at, and away from, a zone axis). So, for example, in a compound AB+X, NX, the integrated x-ray intensity of the element X, is ratioed to both NAand NBfor x-ray spectra acquired at both +sgand -sg. If either NX/NAor NX/NBis independent of sgthis infers that the ternary element occupies the A or B sublattice respectively, thus providing qualitative information. However, if the ternary addition is partitioned between the two sites, this method is unsatisfactory and comparison of the ratios of the x-ray intensities will not provide a clear result.