Atom probe microscopy of strengthening effects in Alloy 718

F. Theska, S.P. Ringer, S. Primig
Microscopy & Microanalysis 25 (2019) 470-480.

This work summarizes our methodical advances in atom probe microscopy that we developed in due course of our research on processing-structure-property relationship of the precipitation hardened nickel-based superalloy 718.

In alloy 718, a complex morphology of stacked nanoscale γ'/γ" co-precipitates is often found. While voltage-mode atom probe yields most accurate datasets for quantification of this complex morphology, premature tip fracture necessitates laser-assisted atom probe in order to obtain statistically significant data. We present corresponding approaches for laser energy calibration and achieve a more accurate quantification via an enhanced iso-surface method. Here, absent crystallographic information demands alternative reconstruction calibration via the precipitate morphology in correlation to voltage-mode atom probe data. Our ‘interface method’ provides the quantitative distinction between coexisting precipitate variants. Finally, a ‘mixed-mode’ atom probe approach offers potential for simplified laser-mode atom probe data reconstruction. These methods may be applicable for atom probe characterisation of various engineering materials.