Point excess solute: A new metric for quantifying solute segregation in atom probe tomography datasets including application to naturally aged solute clusters in Al-Mg-Si-(Cu) alloys

Accurate, repeatable and quantitative analysis of nanoscale solute clustering in atom probe tomography (APT) datasets is a complex challenge which is made more difficult by the positional uncertainty and lack of absolute resolution inherent to the technique. In this work a new method, the point excess solute, is introduced for quantifying solute segregation in datasets with limited spatial resolution. This new method is based on measuring the matrix concentration using a dataset sampling method. We show the new method can accurately reproduce the values expected from synthetic datasets a priori and when the dataset spatial resolution and or phase contrast is too low for accurate quantification this is observable. The method is then applied to naturally aged solute clusters in the Al-Mg-Si-Cu system. Datasets were collected with a range of natural ageing times from 8 min to 76 weeks. The formation of the solute clusters is shown to be unaffected by the Cu content of the alloy