Position artifacts in 3D reconstruction of plate-shaped precipitates in steels depending on the analysis direction of atom probe tomography

Atom probe tomography (APT) analysis often produces artifacts in atomic position owing to the difference in evaporation fields in materials. The atomic density profiles of grain boundaries, plate-shaped low-field precipitates (cementite), and high-field precipitates (vanadium carbide) in steels were investigated via two analyses in directions perpendicular and parallel to the boundaries and platelets. Although the perpendicular analysis indicated better quantitative performances in the composition analyses of segregating atoms at the grain boundary and the constituent atoms of the precipitates, an abnormal atomic density was observed around the interfaces of the precipitates. Geometric calculation using a two-radius model based on the local magnification effect suggested that a spike structure at the front interface and a dip structure at the rear interface for lamellar cementite correspond to an overlap and a gap in the evaporated atoms from the cementite and matrix, respectively. This indicates that even in the perpendicular analysis, the precipitate constituent atoms and matrix atoms mixed in the depth direction. We discuss the origin and impact of the position artifacts in the perpendicular analyses of low- and high-field plate-shaped precipitates and also discussed the application limits of the model.