Site occupations in L12 ordered alloys by axial electron channeling microanalysis

Abstract

Lattice site location of alloying additions to A3B-type ordered alloys with the L12 structure is important for alloy development, but ion channeling and X-ray diffraction techniques require single crystal specimens. The ALCHEMI technique is applicable to polycrystalline specimens but provides only qualitative results on the site occupancy in L12 A3B alloys. Quantitative analysis by standard planar channeling ALCHEMI is complicated by the absence of lattice planes containing only B atoms. Since certain zone axes, including <001> and <111>, contain columns of A atoms well separated from columns of B atoms, the ALCHEMI method has been extended to use zone axis channeling conditions. Further, the procedure has been simplified to use spectra recorded from two orientations - an appropriate channeling zone axis and a “random” non-channeling condition typically 2-5° from the zone. The concentration CX of element X on the B sites is given by Cx = {R(X/A) - 1}/{R(B/A) - 1}, where R(X/A) = (NX/NA)zone/(NX/NA)random, ete., and NX, NA, NB are the characteristic X-ray intensities of elements X, A, and B.