Pile-ups in thin foils: application to transmission electron microscopy analysis of short-range-order

Abstract

The chemical force acting on dislocations in a short-range-ordered concentrated Ni-based alloy is investigated by post mortem and in-situ transmission electron microscopy. For this purpose, the positions of the dislocations in a pile-up are calculated, taking into account the stress relaxation at the free surfaces. The calculation shows that the distribution of the first dislocations of the pile-up is only slightly affected by the presence of the free surfaces, while the length of the pile-up strongly depends on the thickness of the foil. Analysis of pile-ups in two short-range-ordered Ni-based alloys shows that the chemical force resulting from short-range order (SRO) is noticeable up to the sixth dislocation of the pile-up. These results indicate the presence of very small short-range-ordered clusters, rather than a homogeneously distributed SRO.