The atomic structure of A1-B2 interfaces in a NiBe alloy

Abstract

The atomic structure of the interfaces between a Ni-based solid solution with f.c.c.-structure (α-phase) and β-precipitates (NiBe with B2-structure) in a Ni-12 at.% Bi alloy has been investigated by field ion microscopy (FIM) and computer simulation of the images. The precipitates were found to be plate-shaped with an aspect ratio of about 10. Most of the plates were formed roughly but not exactly on (001)-planes of the matrix. The phase boundary is extremely narrow and does not exceed 2–3 atomic layers in thickness. The orientation relationship between α- and β-phases was found to be the Baker-Nutting one, where (001) α//(001) β with 〈110〉 α//〈110〉. The observed morphology of the precipitates and the structure of the interfaces were analysed on the basis of an anisotropy of the interfacial energy, the effect of the elastic strains set up during the phase separation and the growth mechanism of the precipitates.