International audienceIn this study, atom probe tomography was used to investigate the microstructure of the alloy AA2198 (Al-1.35 Cu-3.55 Li-0.29 Mg-0.08 Ag) over a range of ageing conditions to examine the evolution of phases in the alloy, in particular aiming to reveal the nucleation mechanism of the strengthening T-1 phase. T-1 precursor phases were observed from early ageing, most of which were connected to dislocations enriched with Mg and Ag. This Mg solute segregation on the dislocations was subsequently observed to develop into S-like phases. Ag and Mg segregation to T-1 interfaces was systematically observed when the plates were oriented perpendicular to the probing direction. The matrix solute content was followed during the course of T-1 precipitation. It was found that the evolution of Cu, Li, Mg and Ag was similar, giving additional evidence for their co-precipitation

Modern wide field-of-view atom probes permit observation of a wide range of crystallographic features that can be used to calibrate the tomographic reconstruction of the analyzed volume. In this study, methodologies to determine values of the geometric parameters involved in the tomographic reconstruction of atom probe data sets are presented and discussed. The influence of the tip to electrode distance and specimen temperature on these parameters is explored. Significantly, their influence is demonstrated to be very limited, indicating a relatively wide regime of experimental parameters space for sound atom probe tomography (APT) experiments. These methods have been used on several specimens and material types, and the results indicate that the reconstruction parameters are specific to each specimen. Finally, it is shown how an accurate calibration of the reconstruction enables improvements to the quality and reliability of the microscopy and microanalysis capabilities of the atom probe.