Advancements in atomic-scale analytical methods and their application to understanding materials

Abstract

Atom probe tomography is a high resolution microscopy technique capable of determining the 3D location and chemical identification of individual atoms within a specimen. Though it is becoming ever more popular, a number of issues with the technique are known. First, the large amount of data created by atom probe tomography experiments requires new techniques to be developed so as to conduct effective analysis. Also, atom probe tomography is not traditionally considered a tool for crystallographic analysis even though crystallographic information is known to be present in reconstructed datasets. Though prior work has been done, the field of atom probe crystallography is underdeveloped. Furthermore, artefacts in the atom probe experiment and reconstruction are complicated and influence the resulting tomograms in subtle ways. The effects of these artefacts need to be understood so as to properly interpret atom probe results. This thesis contains seven manuscripts which discuss these issues. First, three manuscripts are presented which outline the development 3D orientation mapping of crystal grains in atom probe data, current computational approaches to atom probe data and a new framework for conducting crystallographic analysis of atom probe data. A fourth paper is presented which outlines and applies a new method to define and extract grain boundaries in atom probe datasets. Two papers are presented which discuss artefacts present in atom probe data, how they influence reconstructions and how to minimise errors resulting from these artefacts. A final manuscript is presented which applies several of the developed techniques to the analysis of the aerospace alloy, AA2198. Here, the microstructural evolution of AA2198 is characterised with particular emphasis on the strengthening T1 phase.